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5th Grade Forces
20151102
www.njctl.org
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Table of Contents
• Motion Review
Click on the topic to go to that section
• Forces Review• Gravity
Teacher
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Motion Review
Return toTable of Contents
5
Distance
How far away is your teacher's desk?
How many steps do you have to take to reach the bathroom?
How far do you have to walk to get to the chalkboard?
Teacher
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Distance
________________ is how we measure how far away an item is.
"The chalkboard is 7 steps away."
"The desk is 3 steps away."
"The bathroom is 29 steps away."
Those questions have one thing in common what is it?
Answ
er
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Units of MeasurementThere are different units of measurement used all around the world.
In many other countries, such as Spain, France, and Germany, meters are the basic unit of measurement, known as Metric system.
In America, we use inches and feet as our basic units of measurement, know as US Standard Units.
Scientists use the metric system as their basic units of measurement.
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DistanceThe farther away something is, the _______________ its
distance is from you.
The closer something is, the ______________ its distance is from you.
What's farther from you now, your desk or where you live?
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1 Which object is the closest to you (the shortest distance from you)?
A Your house
B The moon
C The sun
Answ
er
D The North Pole
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2 When talking about how far away something is from you, we use the word ____________.
A time
B distance
Answ
er
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TimeWhat takes longer to do, watching a TV show or washing your hands
after dinner?
To determine the answer, we need to measure ____________.
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SecondMinuteHourDayWeekYearsDecadeCenturyMillennium
TimeTime is used to show how long it takes to do something.
What are some units we use to measure time?
Think about very small measurements and very large measurements!
Make a list with the students at your table and be ready to discuss with the rest of your class and the teacher.
Move clock to reveal answers.
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3 If you measured how long it takes to walk from your house to your friend's house with a stopwatch, you would be talking about ___________.
A time
B distance
Answ
er
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4 If you measured how long your desk is, you would be talking about _____________.
A time
B distance
Answ
er
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5 If you were timing how long it took to walk a mile, you would probably use _______ as your unit.
A seconds
B hours
C minutes Answ
er
D seconds
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6 If you were timing how long it took to blink your eyes, you would probably use _______ as your unit.
A seconds
B minutes
C hours
D days
Answ
er
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7 If you were timing how long it took to fly from Africa to Spain in a airplane you would probably use ________ as your unit.
A seconds
B minutes
C hours
D days
Answ
er
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8 Which of these activities takes the shortest time to do?A Eat dinner (thirty minutes)
B Brush your teeth (two minutes)
C Watch a movie (hour and a thirty minutes)
D Take a shower (eight minutes)
Answ
er
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How Fast Do You Go?The word _____________describes how fast or how slow you go.
How do you know whether you are going fast or slow?
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Speed
Objects with more speed can move a greater distance in a set amount of time.
That is why the fastest runner reaches the finish line first.
We have now related, or combined, two separate quantities, distance and time, to define speed.
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Speeds & Distance
Objects with less speed move a shorter distance in a set amount of time.
That is why it takes you longer to move somewhere if you are walking instead of running.
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Calculating SpeedEarlier we said that when distance and time are used together, they
define speed. Here is how it works mathematically.
Speed is distance divided by time.
Speed =
Moving 10 meters in 5 seconds gives you a speed of
(10 meters ÷ 5 seconds) ________ meters per second.
DistanceTime
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Units of SpeedSpeed is the measure of distance divided by time. To express speed
it is expressed as follows:
Distance per time
Figure out the units of speed for the following:
Distance Time Unit of Speed
Miles Hours
Feet Second
Kilometers Hours
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9 On a bike, your ride 30 meters in 5 seconds. What is your speed?
A 7 meters per second
B 6 meters per second
C 5 meters per second
D 6 seconds per meter
Answ
er
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10 A baseball is thrown 26 meters in 2 seconds. What is its speed?
A 13 seconds per meter
B 24 seconds per meter
C 28 meters per second
D 13 meters per second
Answ
er
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11 Which of the following is faster?
A block
B baseball
Answ
er
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12 Which of these is the slowest?
A A walking man
B A running track star
C A speeding car Answ
er
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13 You slide a book, which moves 6 meters in 2 seconds. What is its speed?
A 2 meters per second
B 3 meters per second
C 4 meters per second
Answ
er
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Forces Review
Return toTable of Contents
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What is this character doing?
Forces
What is this character doing?
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Creating ForceWhen you push or pull something, you are using a force! In fact all forces involve either a push or a pull. Force is not something you
can see or touch. It is an action.
Forces can change the direction of an object, turn things or change the shape of something.
Forces are an important part of physics and are found everywhere!
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Types of ForcesForces are divided into two different types:
Contact forces and Distant forces.
Contact forces occur when an object comes in contact
with another object.
Distant forces occur when two objects are not in contact
with each other.
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Contact & Distant Forces
• Electrical Force• Magnetic Force• Gravitational Force
Can you think of an example of each of these forces?
Contact Forces Distant Forces
• Applied Force• Frictional Force• Normal Force
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Measuring Force
By the way, where did the word Newton come from?
Similar to how we can measure distance in _________ and time in ___________, we measure force in a unit called a Newton (N).
A Newton is how much force is required to make a mass of one kilogram go faster at a rate of one meter per second.
Teacher
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14 Which of the following is not true about forces?
A Forces can change the motion of an object.
B Pulling is the only type of force that impacts an object.
C A force is an action you cannot see or touch.
D Forces can change the shape of things.
Answ
er
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15 Force is measured by
A Meters per second
B Joules
C Kilograms
D Newtons
Answ
er
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16 The picture is an example of what type of force?
Answ
er
A Distance Force
B Contact Force
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Applied ForceApplied force is a contact force exerted on an object either by a
person or another object.
The person pushing the car along the road is applying force upon the car.
What is an example of applied force that involves pulling?
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Motion
When you apply force by ________ or _________ on something and make it move, you are causing motion!
The harder you push or pull on something while it is moving, the more you change its motion.
More force leads to more change in speed.
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Counteracting Motion
Imagine a ball rolling towards you. When it gets to you, you can push the ball away from you and slow it down.
If you keep pushing hard enough, you can stop the ball.
Just as applying force to an object can cause it to move, applying force to a moving object can counteract the motion, causing it to stop.
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Limited Motion
If you kick a soccer ball, it won't travel forever. It eventually stops.
What pushes back on the ball to make it stop?
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Friction ForceThe ball stops its motion due to a force called friction.
Friction is the force from two surfaces rubbing against each other. Friction is always present when two objects rub against one another.
Friction
Motion ofthe ballWhat two objects
are rubbing in thisexample?
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Friction The friction force always acts against the object's motion. It always tries to slow things down.
The amount of friction depends on the texture of the surfaces. Rougher surfaces have more friction.
A hockey puck skidding across ice goes a long distance before it stops. What if you slid a hockey puck across the sidewalk?
In which case was there a smaller friction force?
Note
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Normal ForceNormal force is the support force a stable object exerts on another
object.
When a book is sitting on a table it exerts its force down on the table. The surface of the table is exerting force upwards to support the weight of the book.
What examples of normal force do you observe around the room?
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17 Friction force involves:
A two surfaces rubbing against each other
B a force applied to an object by a stationary object
C movement caused by applied force
D objects do not contact each other
Answ
er
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18 Which of the following is not an example of an applied force?
A Kicking a football
B Typing on a keyboard
C Pulling a wagon
D Sitting on the couch
Answ
er
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19 Normal force occurs when
A a moving object applies force to a stationary object
B a force is applied to an object, causing it to move
C a stable object exerts supporting force on another object
D two surfaces rub against each other
Answ
er
C
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Determining Forces ImpactWe already know that a force is either a push or a pull.
When you push on a ball, it moves. But when you push on a wall, it doesn't. Why?
When you play tug of war, even though both sides are pulling, the rope only moves in one direction. Why?
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Balanced and Unbalanced ForcesThe answer is because of balanced and unbalanced forces!
What do you think it means if a force is balanced?
What do you think it means if a force is unbalanced?
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10 Newtons 5 Newtons
Net ForceIn order to understand balanced forces, we should first understand net force. Net force is the total force applied to an object.
Who is going to win this tug of war? How do you know?
What is the net force?
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Calculating Net ForceForce is measured in terms of Newtons and is abbreviated with N.
1 Newton = .22 poundsforce
10 N of force is applied on the left side and 5 N of force is applied on the on the right side. The net force is (10 N 5 N) = 5 N of force to the left.
10 Newtons 5 Newtons
The rope and the people move to the left because of the net force of 5 N to the left
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Net Force Problem
If you push with 15 N of force on the left side of a box, and push with 6 N of force on the right side of a box, what will the net force on the box be?
6 N15 N
?
Make sure your answer includes the direction of the net force and the size (number) of the force.
Answ
er The net force is (15 N 6 N) = 9 N to the left.
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B 5 N to the left
20 What is the net force applied to this box?
3 N 8 N
A 11 N to the right
C 11 N to the left
D 5 N to the right
Answ
er DThe net force is
(8 N 3 N) = 5 N to the right.
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21 What direction will the ball move?
A right
B left
C It will not move.
9 N 4 N
D To the right and then to the left
Answer
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Balanced ForcesBalanced forces are two forces, equal in size, acting in opposing directions on the same object.
When the forces on an object are balanced, the object does not move OR stays moving at a constant speed.
Each hand is pushing on the box with 5 N of force. What is the net force?
Answer
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More Balanced ForcesWhen a book lies on a table, the forces on it are balanced. Gravity pulls down on it, but the table pushes up on it.
Table pushes up on the book
Gravity pulls down on the book
(gravitational force)
As a result, the book doesn't move.
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Balanced Forces ExamplesWhat are some examples of objects having balanced forces?
With a partner, come up with a list of 5 examples.
Teacher
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Unbalanced ForcesIf the opposing forces are not equal, then they are unbalanced. When you throw a bowling ball, you are applying an unbalanced force on the pins.
Can you think of 3 other example?
Teacher
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22 A student applies 10 N of force to the left side of a box. Another student applies 10 N to the right side of the box. What is the net force applied to this box?
B 0 N
A 10 to the right C 10 N to the left
D 20 N
Answ
er
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23 Which of the items would not move?
3 N 10 NA
B
C 15 N15 N
8 N 4 N
Answ
er
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24 Which of these represents an unbalanced force?
ATwo forces push a box, resulting in a net force of 0 Newtons.
B A student pushes on a wall and does not move.
C You kick a soccer ball into a goal.
Answ
er
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25 Which of these involves a balanced force?
A Two students push on a car, and it speeds up.
B A book slides to a stop across a table.
C Two groups play tug of war, and the rope does not move.
Answ
er
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NonContact ForcesHave you ever seen paper
clips move towards a magnet without touching it?
Why does an apple fall to the ground when you let go of it,
even though nothing is touching it?
Have you been shocked when touching a door knob?
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MagneticForce
ElectricalForce
Distant ForcesAs it turns out, a force is not just a push or a pull with contact between the two objects. Objects can apply a force to one another without actually touching. Things do not have to touch to cause a change in motion. These are known as distant or noncontact forces.
What are the names of the distant forces from the last slide?
Click to reveal
GravitationalForce
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Distant Forces
Electrical, magnetic and gravitational, forces are all examples of distant forces. These forces apply a force on another object
without actually touching it.
Gravitational Electrical Magnetic
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Magnetic ForceMagnets are any object that tends to push or pull on one another and certain other objects.
The magnets create a magnetic field around themselves, and when these objects enter the field, they feel a force without touching the actual magnet! Do magnets attract all objects?
This is a horseshoe magnet it isa magnet bent in a U shape.
Teacher
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Magnetic Field
Magnetic fields are represented by drawn lines so we can understand how they affect objects. The arrows indicate the direction of travel of the magnetic field and how noncontact forces can push and pull objects.
Magnetic field lines
Do you ever see those lines around a magnet?
A magnetic field is the area in which a magnet can apply a push or pull force without touching the magnetic object. Magnetic objects in a magnetic field can be attracted or repelled by the magnet.
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Visualizing Magnetic FieldsDo you ever see those lines around a magnet? Of course not! However, covering a magnet with a piece of paper and sprinkling metal filings on top of it reveals with those same lines.
Check out this video on magnetic fields
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Limits of Magnetic Force
The farther an object is from the center of a magnetic field, the weaker the force it feels from the field.
You might notice sometimes magnets don't work if they are far from another magnetic object.
Why are the nails at the top of the image not being pulled towards the magnet while the bottom ones are?
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The nails at the top are far away from the magnet to be affected enough by the magnet to move. Where the upper tacks are, the field is too weak.
The tacks are too heavy for the magnetic force to make them move by pulling on them.
Magnetic Force
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Polarity of MagnetsMagnets have a North and South pole. The magnetic field goes from the north pole to the south pole. This is why like poles repel each
other, and opposite poles attract each other!
Attracting Forces Repelling Forces
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Earth's Magnetic Field
Earth itself is actually one giant magnet. It has its own magnetic field.
This is how a compass works. The metal arrow lines up with the magnetic field of Earth.
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26 Which of the following is not true about magnetic force?
A Magnetic fields are the area around a magnet that can push or pull another magnetic object.
B Opposite poles attract one another.
C Magnetic force flows from the north pole to the south Pole of a magnet.
D Like magnetic poles attract one another.
Answ
er
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27 Which location would experience the greatest magnetic force?
A Location 5
B Location 3
C Location 1
Answ
er
D All locations experience the same magnetic force.
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28 You have a magnet that has the North and South pole marked. How can you use this magnet to determine the North and South pole of other magnets?
Discuss this at your table.
Click "A" on your responder when you are ready to share your ideas.
Answ
er
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Another Invisible Force
Did you ever get to school and notice you have your pet's hair stuck to your
clothing?
Why does that happen?
Have you ever taken off your jacket and your hair is
standing up?
Why does that happen?
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Electric ForceThe force behind these effects is called an electric force. All objects have a property called a charge, which can be either positive or
negative.
Just like how magnets have two poles, (north pole and south pole), the two kinds of charges are called positive (+) and negative (). Electric force is how these charges interact with one another.
Also, just like magnetic force, electric force is a noncontact force.
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Electric Force InteractionsWhen the same magnetic poles come near each other,
what happens? Click the image to reveal.
When two different charges come near each other, what happens? Click the image to reveal.
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Electrical ForceWhen there are two of the same types of charges, they repel.
When there are two different charges, they attract.
Positive and Positive REPEL
Negative and Negative REPEL
Positive and Negative ATTRACT
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Electric Force All Around Us
Nearly all objects can feel an electric force and move because of it.
What does that tell you about the charge on things in most cases? Are you completely made up of positive charge?
Negative charge?
Most of the time, however, you do not feel a strong attraction to the wall or the person standing next to you or any object near you.
Answ
er
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29 Which of the following statements about electrical charges is true?
A Electrical charges can be positive or negative and have north and south poles.
B All electrical charges are negative.
C Electrical charges are positive or negative but do not have a north or south pole.
Answ
er
D All items have an electrical charge that is either north or south.
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30 Many objects, like a chair or a wall or your hair, are considered to have a _______ charge.
A Positive
B Negative
C Neutral (no charge)
Answ
er
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31 Which of the following is true about the pair of charges below?
A Pair 1 will repel and Pair 2 will attract.
B Both pairs will attract.
Pair 2Pair 1
C Pair 2 will repel and Pair 1 will attract.
D Both pairs will repel.
Answ
er DSimilar forces repel each
other.
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Electric Force ExperimentIf you blew up a balloon and put it next to the wall, would it stick?
Try it now.
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Neutral Electric ForceYou probably found it did not stick to the wall.
Most of the time, objects like your hair and the balloon have the same amount of positive charges as negative so they are neutral
and there is no electric force to move them.
How can you make the balloon stick to the wall?
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+++ ++ +++
Charges On The MoveYou would rub the balloon on your hair and then put it next to the
wall. So what is the scientific way to explain this?
First, the friction of rubbing the balloon moved a bunch of negative charge from your hair to the balloon!
This made the balloon negatively charged.
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+
+
+
+
++
+
+
When the balloon is placed near the wall, it pushed away the negative charges in the wall. That would leave positive charges in
the wall near the balloon.
Electric Force
These positive charges on the wall's surface now attract the balloon, so the balloon sticks to the wall.
+
++
+
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Changing Electrical ChargesHere's another way to understand it. As you rub a balloon on your head, you are charging it by giving it negative charge. This turns the balloon into one huge negative charge.
This causes the positive charges in the wall to pull on the negative balloon and attract it to the wall!
+
++opposite charges attract
like charges repel
+
++
+
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Electric Force Examples
Electric force is not just limited to balloons. This also applies to many other objects!
Remember the example of your pet's hair stuck on
your clothes?
Can you think of any other examples?
Teacher
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Electric Force DemonstrationClick on the image to access a demonstration which shows how rubbing a balloon on a sweater can cause it to become attracted to a wall.
Pay attention to the changes in the charges.
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32 If you put a balloon with negative charges next to a sweater with positive charges, the balloon will move towards the sweater.
True
False
Answ
er
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33 Which statement about electric force is true?
A Electrical charges, both positive and negative, can be transferred from one item to another.
B Only positive electrical charges can be transferred.
C Positive and negative electrical charges cannot be transferred.
D Only negative electrical charges can be transferred.
Answ
er
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34 If you put a comb with positive charges next to another comb with positive charges, they will move towards each other (attract).
True
False Answ
er
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Net ChargeHow can you determine the electric charge of an item?
Net charge is the total charge of an object is determined by the number of protons (+) or electrons (). For example, if an object has 5 electrons and 4 protons, the electric charge is positive
because there are more protons.
What is the net charge of the following items?
+ +
+
++
+++
+
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+
++
Calculating Net ChargeIf an object contains the same amount of positive and negative charge the net charge of the object is zero or electrically neutral.
+ +
+++
+
Positive Negative3 3 = 0
Net Charge
Positive Negative2 5 = 3
Net Charge
Positive Negative4 2 = +2
Net Charge
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+ +
+ +++
Transfer of ChargesElectrical charges can not be created or destroyed, but rather transferred from one object to another. When you rubbed the balloon on your hair, electrons from your hair transferred to the
balloon.
+ +
+ +++
What is the net charge of the hair now?
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35 What is the net charge on an object with 8 positive charges and 5 negative charges?
A Positive
B Negative
C Neutral Answ
er
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+ +
+
36 Which of the following has a neutral net charge?
A B
C D
+
++
++
+
Answ
er
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37 Which of the following statement below is true?
A Charges are transferred from smaller objects to larger objects.
B Electrical charges can be transferred from one object to another but cannot be created or destroyed.
C Electrical charges can be created or destroyed and transfer between objects.
D Electrical charges cannot be created, destroyed or transferred from between objects.
Answ
er
B
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After we talked about magnetic forces, what other word did we come up with to explain how the forces acted without touching the other magnetic objects?
Types of Force Fields
What kind of field do you think we have in the charged balloon example?
??
Teacher
101
Just like magnetic forces making a magnetic field, electric forces make an electric field that acts in similar ways.
Other charged objects feel the electric force through the electric field. Just like the magnetic field, you can't see the electric field. But it does tell you which way the electric force will push or pull
something.
Electric Fields
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The area around electrically charged items look and act similar to a magnetic field. Any item that enters an electric field will feel the force because all items have an electric charge. The lines around
an electrical charge indicate the direction of the charges.
Similar Fields
Attracting Repelling
103
The strength of an electric field is directly related to its distance and size. The closer an electric field is, the stronger its effect will be. Further, its strength will also increase with the size of the
charge producing the field.
Electric Field Strength
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38 Which of the following represent an attracting electric field?
A B
C D N S
N S
Answ
er
105
39 Electric forces and magnetic forces are examples of __________ forces.
A Non Contact
B Variable
Answ
er
C Contact
D Visible
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40 The strength of an electric field depends upon its ___________ and ___________.
A shape & number
B shape & distance
C orientation & size
D size & distance
Answ
er
107
41 When we talk about different charges attracting or repelling, we are talking about what type of force?
A Magnetic Force
B Electric Force
C Gravitational Force
Answ
er
108
Lab: Electric Field Hockey
Use your knowledge of electric fields and manipulate positive and negative charges to score a goal in this virtual hockey game!
http://phet.colorado.edu/en/simulation/electrichockey
109
Gravity
Return toTable of Contents
110
There are contact and noncontact forces.
What are the two noncontact forces that have been covered so far?
This section will cover a third noncontact force.
The Third Force
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This force is probably the most familiarto you. If you were to hold an apple,and then let it go, which way would it go?
Did you have to throw it to make it move?
Since it wasn't moving, and then itstarted moving what had to be appliedto it?
Constant Force
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The force that caused the apple to move is called Gravitational force.
Gravitational force has been studied since ancient times. Magnetic and electric forces, however, had to wait on the development of more complex measuring techniques and equipment. It wasn't until the 17th century when their secrets started to be revealed.
Gravitational Force
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Gravitational Pull
The cow jumps off the diving board. Initially, she goes up in the air, but the Earth is pulling on her, and she splashes into the water.
Did you also know that the cow is also pulling up on Earth?
Gravitational force occurs when two bodies physically attract each other by "pulling."
Note: The cow was not harmed she easily paddled her way to the end of the sloping pool and went back to pasture.
114
Gravitational force is also why the moon does not move away from Earth, but revolves (goes around) it.
That last concept is a little tricky why doesn't the moon fall towards Earth like the apple or the cow?
Holding Space Together
The moon is actually constantly falling towards the Earth! Why does it never hit Earth? More on that later.
115
Aristotle Aristotle was a great philosopher in ancient Greece who wrote about philosophy, science, logic, poetry, politics and many other things. He knew a lot!
In 350 B.C., he wrote about physics and, specifically, gravity.
Unlike scientists of today, he performed noexperiments and made no measurements heobserved the world around him and wrotedown his thoughts of how it worked.
Why is this not a good way of doing science?
Discuss with a partner how scientists solve problems.
116
Aristotle's Observations
Observation, of course, is one of the first steps of doing science.
Thinking of why the world works like it does is next.
Next, you have to actually measure what is happening and predict something new based on the measurements and experiments.
This is the only way that you know your thoughts actually describe the world. It also leads to discoveries of new things.
117
Properties of Gravity Aristotle was interested in how the mass (weight) of an object affected how fast it fell.
He observed that heavier objects fell faster than lighter objects so when a feather and a rock were dropped from the same height, the rock would hit first. Why?
Aristotle did not carry out any further experiments on this topic, and it wasn't until the end of the 16th century that people did experiments and found out that Aristotle was wrong!
Teacher
118
Galileo Galilei
Galileo was one of the first people to use the scientific method where he combined observation, theory, mathematics and experimentation.
A famous experiment has been creditedto Galileo. It has been repeated by many other scientists.
It involves two towers in Pisa, Italy, and wasdesigned to see if objects of different weightfell at different speeds.
119
Leaning Tower of Pisa
In Italy, there is a tower in the town of Pisa that leans to the side. Objects were dropped from the top of the tower.
Many experiments were performed to see if heavier objects fell faster than lighter objects.
Galileo believed that if similarsized objects with different weights were dropped at the same time from the tower they should land at the same time.
120
Falling Objects Experiment
If the weight made a difference, the tower was high enough to see a noticeable difference in how long each took to hit the ground.
Two balls of different weight (but thesame size) were taken to the tower ring. They were dropped many times. Each time, they both hit the ground at the same time.
121
Aristotle had proposed that heavier objects fall faster than lighter ones. Galileo wasn't so sure about that.
Instead of arguing, he designed an experiment. The experiment was carried out and proved Aristotle wrong.
This is the scientific method in action. Part of science is proving established theories wrong and developing new ones.
Scientific Method In Action
122
Different Sized and Shaped Objects
But, what if a feather was dropped at the same time as a cannon ball? Which would hit the ground first?
Hint there is a contact force acting here because of the air.......
VS
123
The cannonball would hit first!
Air friction slows down lighter objects more than heavier objects and doesn't give us the expected result.
Different Results
Why does air friction affect the cannon ball and feather
differently?
Where could we go where air friction wouldn't be a problem?
Can you think of a place with no air?
124
In space there is no air since it a vacuum. On the moon In 1971, an American astronaut, David Scott, held a hammer in one hand and a feather in the other and did an experiment during a moonwalk. He dropped both at the same time. What do you predict happened?
Falling Objects Moon Experiment
Click here to see video
125
Did you notice anything unusual during the demonstration?
Moon Experiment Results
Both objects fell with the same speed that's good. But the hammer fell at a much smaller speed then it would have on Earth. That is because the force of gravity on the moon is less than that on the Earth that will be covered later in the unit.
Click to reveal answer
Click to reveal
126
Gravity In a Vacuum
This experiment also works on earth in a special tube called a vacuum chamber. A vacuum in science is an empty space. There is nothing in a vacuum, not even invisible gases like oxygen. Just like the moon!
In this demonstration, a metal disk and a feather are dropped from the top of the chamber.
What do you see?
Click here to see video
Teacher
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42 If a sheet of paper and a rock were dropped from the roof of your school at the same time, which of the following would be true?
A The rock would hit the ground first because it is heavier.
B The paper would hit the ground first because it is thinner.
C The paper would hit the ground first because it has a bigger surface area and experiences more gravitational pull.
D Due to the friction and resistance from the air on the paper, the rock would hit the ground first.
Answ
er
128
43 A ping pong ball and a pool ball are placed in a vacuum chamber and dropped from the top at the same time. Which object reaches the ground first?
A Ping pong ball
B Pool ball
C They hit at the same time.
Answ
er
129
44 Two objects of exactly the same size but different weights were dropped from a tower at the same time. Which of the following would you expect to happen?
A The lighter object would hit the ground first.
B Both objects would hit the ground at the same time.
C The heavier object would hit the ground first.
D None of the above would occur.
Answ
er
B
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45 Why do two objects dropped on the moon behave differently than if they were dropped on the Earth?
A The gravity on the moon is more than the gravity on Earth.
B Both objects would hit the ground at the same time.
C The heavier object would hit the ground first.
D None of the above would occur.
Answ
er
B
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Sir Isaac Newton
In 1687, Sir Isaac Newton published Principia, which explained nearly everything that had to do with moving objects, as well as creating advanced mathematics to solve and predict the motion of objects.
Newtons work on gravity expanded upon the ideas and theories from Galileo's experiments.
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Newton's Discovery
Many books report that while sitting outside after dinner with a friend, Newton saw an apple fall from a tree and hit the ground and then discovered gravity.
While it may have been shocking for Newton, that's not quite true. People knew for a long time that falling objects fall down!
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Not This
Rules of GravityWhat Newton did was to apply mathematics to the falling apple and proved why objects fall in a straight line apples don't fall off a tree and go in circles they fall straight towards the center of Earth.
His equations also illustrated the strength of gravitational force. He used mathematics to explain the world around him.
This
134
The gravitational forces on Earth pull any object near or on Earth's surface down towards Earth's center. What other objects experience the gravitational force from Earth?
Earth's Gravitational Pull
135
Earth's Gravitational ReachNewton discoveries went one tremendous step beyond apples. He made the bold statement that the same gravitational force that attracted the apple to Earth also attracted the Moon to Earth!
But how can that be? The apple hits Earth, but the Moon goesaround Earth.
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Delicate BalanceThe Moon is constantly falling towards the center of Earth. But, the moon moving so fast in a direction perpendicular to Earth, that it moves in an ellipse around the Earth.
The combined effects of the moon's own gravitational pull and its perpendicular velocity keep the moon in orbit around the Earth.
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Simulating an OrbitYou can simulate this motion by swinging a ball, attached to arope, above your head. You are pulling in on the ball (like gravity), but it is moving so fast, that it goes in a circle.You are acting as Earth, the rope is standing in for the gravitational force, and the ball is like the Moon.
What happens the ball when gravity is not present?
138
46 Who explained gravity using specific mathematical language?
A Aristotle
B Galileo
C Newton
D Plato
Answ
er
139
47 In which direction does Earth's gravitational force pull objects?
A Up and away from the Earth
B Opposite of the Earths' rotation
C Down, towards the center of Earth
D In the directin of the Earth's rotation
Answ
er
140
Lab: Race to the BottomWhen items are dropped on Earth, they experience not only the force of gravity but also the frictional force of air resistance.
In this lab, put your knowledge to the test.
Can you hypothesize which item will hit the ground first?
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Properties of the Gravitational Force
Here's what Newton said about gravity:
1. It is an attractive force between objects and each object pulls on the other one with the same force. The force increases as either object gets bigger.
2. Every object, whether big or small, creates a gravitational field. Other objects within this field feel an attractive force.
3. The distance between the centers of the objects changes the strength of the force.
Let's look at each of these points individually.
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Principle #1 Attractive Force
Gravity is an attractive force between objects and each object pulls on the other one with the same force. The force increases as either object gets bigger.
Remember, magnetic and electric forces can either attract or repel. Gravitational forces can only attract.
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Unlike magnetic and electric fields, a gravitational field depends on the mass of the objects.
To measure a gravitational force, the object must be gigantic!
Each object pulls on the other one with the same force this means that as Earth pulls on the apple, the apple is pulling on Earth!
So, why do you see the apple moving and not Earth?
Principle #1 Attractive Force
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The forces are exactly the same. But, Earth is so incredibly big and heavy, that the force can't budge it at least not that we can measure.
However, the same force applied to a tiny apple, moves it quite quickly.
What would happen if everybody on Earth jumped up and then down at
the same time?
Move Earth for the answer.
Nothing! Earth is too big to even feel it.
Principle #1 Attractive Force
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Newton realized that all objects have a gravitational pull that attracts other objects.
However, as the mass of the object increases, so does its gravitational pull on other objects. Most objects are too small to exert a significant gravitational force on other objects.
What objects are huge and relatively nearby?
"You can't measure my gravitational pull."
"Or mine unless you have very expensive and complex tools."
Answ
er
Principle #1 Attractive Force
146
48 There is a very small gravitational force that attracts ants to humans. Is there the same gravitational force attracting humans to ants?
Yes
No
Answ
er
147
49 The more mass (weight) something has, the more gravitional force there is acting on the object.
True
False
Answ
er
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Principle #2 Gravitational Field
Every object, whether big or small, creates a gravitational field. Other objects within this field feel an attractive force.
Any object within Earth's gravitational field will feel an attractive force towards Earth.
However, the same can be said for the gravitational field around an ant. All objects have a gravitational field.
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The distance between the centers of the objects changes the strength of the force.
Like magnetic and electric fields, a gravitational field decreases as distance increases between the two objects.
Gravitational force depends on distance.
Principle #3 Force vs Distance
Fgravity = 1/4
Fgravity = 1
Fgravity = 1/9
1
2
3
In which pair is the gravitational force the smallest?
This pair is farthest apart so has the smallest gravitational force.
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Newton understood that as the distance between two objects increased, the gravitational force between them decreased.
For two objects that are double the distance, the force is only 1/4th as strong! If the distance is tripled, the force is only 1/9th!
.
Fgravity = 1/4
Fgravity = 1
Fgravity = 1/9
1
2
3
Principle #3 Force vs Distance
Teacher
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50 Which of these has the greatest force of gravity on an object on its surface?
A Earth
B Sun
C Moon
D Not enough information
Answ
er
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51 Where would the force of gravity due to Earth be the strongest?
A On Earth's surface
B 10 m away
C 100 m away
D 1,000,000 m away
Answ
er
153
52 Does the Sun exerts a gravitational force on Earth?
Yes
No
Answ
er
154
53 Does Earth exert a gravitational force on the Sun?
Yes
No
Answ
er
155
54 On the side of Earth opposite you, things fall up, away from Earth.
True
False
Answ
er
156
55 Is there a gravitational force on Saturn due to Earth?
Yes
No
Answ
er
157
56 The gravitational force is greater on an object that is _________ meters away.
A 10
B 15
C 20 Answ
er
158
Gravity Simulation Lab
How do mass and distance affect the strength of a gravitational field? See for yourself in this virtual lab.
On the International Space Station, astronaut Marsha Ivins feels the pull of gravity differently than when she is on Earth.
http://phet.colorado.edu/en/simulation/gravityforcelab
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