Physics Science AS1.6. NSF North Mississippi GK-8 Topics to be covered Energy Work & Power Heat Motion Forces Momentum Electricity.

PhysicsPhysics

Science AS1.6Science AS1.6

NSF North Mississippi GK-8NSF North Mississippi GK-8

Topics to be covered

Energy Work & PowerHeatMotionForcesMomentumElectricity


Its about calculationsIts about calculations

Don’t panic!!Don’t panic!!Read the question Read the question CAREFULLYCAREFULLYWHY?WHY?The examiners will often give you the two The examiners will often give you the two variables that you need to complete the variables that you need to complete the calculation.calculation.Check your answer – is it reasonable Check your answer – is it reasonable and realistic? If not, you’ve made a and realistic? If not, you’ve made a mistake!!mistake!!


Achieve, Merit, ExcellenceAchieve, Merit, Excellence

Achieved questions – purely calculations Achieved questions – purely calculations given the variables.given the variables.

Merit questions – calculations where you Merit questions – calculations where you use the variable from the achieved part of use the variable from the achieved part of the question.the question.

Excellence questions – calculations up to Excellence questions – calculations up to a merit level with some discussion on the a merit level with some discussion on the effects of different values of the variables.effects of different values of the variables.


How it worksHow it worksYou get marks for the You get marks for the whole calculation –whole calculation –

1.1. State the formulaState the formula

2.2. State the variablesState the variables

3.3. Do the calculationDo the calculation

4.4. Get the answerGet the answer

5.5. Remember the units – Remember the units – the answer is no good the answer is no good without them. without them.


StarterStarter

Name three non-contact forces:Name three non-contact forces:


Contact vs non-contact forcesContact vs non-contact forces

Contact forces: Touch the object they are acting Contact forces: Touch the object they are acting ononPushingPushingPullingPullingTwistingTwisting

Non-contact forces: move something with Non-contact forces: move something with touching ittouching itGravityGravityMagneticMagneticElectricalElectrical


ForceForce

Forces act on us all the time.Forces act on us all the time.

We know a force is acting on an object if it We know a force is acting on an object if it deforms or changes the motion of the deforms or changes the motion of the object.object.

Force is measured in Newtons (N).Force is measured in Newtons (N).

The fractions are worked like the metric The fractions are worked like the metric system.system.


If two equal-sized forces act in opposite directions on an object then the net force is zero. The object is said to be in equilibrium.

Balanced forces on a body can be recognised when an objectis (a) stationary. (b) moving at a constant speed.

The forces are balanced,the box does not move


When the action and reaction forces are equal in sizeand opposite in direction they are said to be balanced.If we increase the force from the right what happens?

The forces are now unbalanced, the box moves in thedirection of the imbalance and should do so indefinitelyin a frictionless environment.


Forces are balanced so the object doesn’t move.

Some forces become unbalanced and the object movesin the direction of the extra force.


Movement and unbalanced Movement and unbalanced forcesforces

When the action force is different in size or When the action force is different in size or direction from the reaction force, then the direction from the reaction force, then the forces are said to be unbalanced.forces are said to be unbalanced.

The resultant unbalanced force always The resultant unbalanced force always accelerates an object in the direction of accelerates an object in the direction of the net force.the net force.

This means that an accelerating object is This means that an accelerating object is always acted on by unbalanced forces. always acted on by unbalanced forces.


Calculating the unbalanced Calculating the unbalanced forceforce

For forces acting in opposite directions, For forces acting in opposite directions, the unbalanced force can be calculated by the unbalanced force can be calculated by subtracting the smaller force from the subtracting the smaller force from the larger one.larger one.

The resultant unbalanced force is in the The resultant unbalanced force is in the direction of the larger force.direction of the larger force.

35 N

10 N

25 N

Two opposite forces Resulting unbalanced force


More force rulesMore force rules

80 N + 25 N in the same direction = a single force of . . .

80 N + 25 N in opposite directions = a single force of . . .

55 N + 25 N in one direction and 80 N in the opposite directions =

NO MOVEMENT


ForcesForces

Thrust Friction

Gravity

Support


Weight vs MassWeight vs Mass

Weight: is the defined as the force of gravity Weight: is the defined as the force of gravity pulling downwards on an object and is measured pulling downwards on an object and is measured in newtonsin newtons

Mass: is measured in kilogramsMass: is measured in kilograms

Weight force = mass of object x acceleration due Weight force = mass of object x acceleration due to gravityto gravity

FFgravitygravity = m x g = m x g


Acceleration due to gravityAcceleration due to gravity

On the surface of earth the potential On the surface of earth the potential acceleration of an object due to force of acceleration of an object due to force of gravity is 10msgravity is 10ms-2-2

If your mass on earth is 60kg, the the If your mass on earth is 60kg, the the weight force acting on your body is given weight force acting on your body is given by 60kg x 10msby 60kg x 10ms-2-2 = 600N = 600N



StarterStarter

The passengers in a car of mass 1500kg The passengers in a car of mass 1500kg have the following masses; 125kg, have the following masses; 125kg, 105kg, 95kg, and 75kg105kg, 95kg, and 75kg

Calculate the total mass of the car and Calculate the total mass of the car and passengerspassengers

What would the car and passengers What would the car and passengers weigh?weigh?


QuestionQuestion

My puppy Oatis has a weight of 70N.My puppy Oatis has a weight of 70N.

What is his mass?What is his mass?


m

F

g


StarterStarter


Force, mass, accelerationForce, mass, acceleration

If the net force increases the acceleration If the net force increases the acceleration will also increase. A motor bike can will also increase. A motor bike can produce much more thrust than a scooter produce much more thrust than a scooter so its acceleration will be greater.so its acceleration will be greater.

Acceleration is directly proportional to the Acceleration is directly proportional to the net forcenet force


Force, mass, accelerationForce, mass, acceleration

If the mass of an object increases, then its If the mass of an object increases, then its acceleration will decrease. A scooter with acceleration will decrease. A scooter with a pillion passenger will not be able to drag a pillion passenger will not be able to drag off a scooter with a single rider.off a scooter with a single rider.

Acceleration is inversely proportional to Acceleration is inversely proportional to massmass


The relationship between The relationship between unbalanced forces and accelerationunbalanced forces and acceleration

This is given by the equation.This is given by the equation.

Force (F) = mass (m) x acceleration (a)Force (F) = mass (m) x acceleration (a)

F = m.aF = m.a

Force in newtons, mass in kg and acceleration is Force in newtons, mass in kg and acceleration is msms-2-2


ExampleExample

A toy with a mass of 1.5 kg is pulled by a A toy with a mass of 1.5 kg is pulled by a string and accelerates at 2 msstring and accelerates at 2 ms-1-1. What is . What is the size of the force?the size of the force?

F=m.aF=m.a

= 1.5 x 2= 1.5 x 2

= 3 N= 3 N


ExampleExample

A force of 500 N is used to accelerate a 2 A force of 500 N is used to accelerate a 2 kg object. What is the acceleration?kg object. What is the acceleration?

F=m.aF=m.a

a = F/ma = F/m

= 500/2= 500/2

= 250 ms= 250 ms-1-1


ExampleExample

An object accelerates at 7.5 msAn object accelerates at 7.5 ms-2-2 when a when a force of 15 000 N is applied to it. What is force of 15 000 N is applied to it. What is the mass of the object?the mass of the object?

F=m.aF=m.a

m=F/am=F/a

= 15000/7.5= 15000/7.5

= 2000 kg = 2000 kg



Tandem skydivingTandem skydiving

Ariana is skydiving for the first timeAriana is skydiving for the first timeHer and her jumpmaster have a combined mass of Her and her jumpmaster have a combined mass of

150kg150kg

Using FUsing Fg g = mg find their weight= mg find their weight

They jump out of the plane, one force acting on They jump out of the plane, one force acting on them is gravitythem is gravityName the other force and state the directionName the other force and state the direction


During the free fall the net force acting on adriana During the free fall the net force acting on adriana and the jumpmaster is 825Nand the jumpmaster is 825NCalculate their net acceleration.Calculate their net acceleration.Discuss how when released the parachute Discuss how when released the parachute reduces their speed.reduces their speed.

MotionMotionThis is about the observation, This is about the observation, measurement and analysis of measurement and analysis of

moving bodies. moving bodies.


Acceleration – an increase in an object’s Acceleration – an increase in an object’s speed (or direction) caused by unbalanced speed (or direction) caused by unbalanced forces forces

Deceleration – a decrease in an object’s Deceleration – a decrease in an object’s speed (or direction) caused by unbalanced speed (or direction) caused by unbalanced forces forces


Distance – time graphsDistance – time graphs

It is possible to measure the distance of an It is possible to measure the distance of an object as it moves away from a starting object as it moves away from a starting position and plot this information on a position and plot this information on a graph.graph.

This is called a This is called a distance-timedistance-time graph. graph.


Time (seconds)

Dis

tanc

e fr

omst

art

(m)

accelerating

decelerating

StoppedC

onst

ant s

peed

Constant speed


Time (seconds)

Dis

tanc

e fr

omst

art

(m)

Stopped


Draw the distance-time graphs for Draw the distance-time graphs for the belowthe below

A car traveling at top speed along the A car traveling at top speed along the motorwaymotorway

A Mother bird fetching food for its chickA Mother bird fetching food for its chick

A skateboarder going down a hillA skateboarder going down a hill


Distance, time, speedDistance, time, speed

Distance-time graphs give information Distance-time graphs give information about the speed of an object. The about the speed of an object. The slope/gradient of a distance-time graph slope/gradient of a distance-time graph equals the speed.equals the speed.

Different slopes describe differences in Different slopes describe differences in speedspeed


Speed and velocitySpeed and velocity

An object has speed when it travels a distance in An object has speed when it travels a distance in a given time.a given time.

The formula is:-The formula is:-

Speed (v) = distance travelled (d)/time (t)Speed (v) = distance travelled (d)/time (t)

v = d/tv = d/t


Remember to get the units rightRemember to get the units right

Distance is measured in metres (m)Distance is measured in metres (m)

Time is measured in seconds (s)Time is measured in seconds (s)

Speed is metres/second (m/s or msSpeed is metres/second (m/s or ms-1-1))


VELOCITYVELOCITY

The word scientists use to describe The word scientists use to describe how how fastfast an object is moving an object is moving


Instantaneous and average speedInstantaneous and average speed

At any given instant an object has a At any given instant an object has a speed. This is called instantaneous speed. This is called instantaneous speed. In a car this is measured by the speed. In a car this is measured by the speedometer.speedometer.

The average speed, is the speed of an The average speed, is the speed of an object during a given period of time.object during a given period of time.

It takes into account the many different It takes into account the many different instantaneous speeds during the journey.instantaneous speeds during the journey.


Average speedAverage speed

The distance becomes the total distance The distance becomes the total distance travelled.travelled.

The time becomes the total time taken to The time becomes the total time taken to complete the journey.complete the journey.

An exampleAn example

The bus to school travels at a number of The bus to school travels at a number of different (instantaneous) speeds at it stops and different (instantaneous) speeds at it stops and starts, but at the end of the journey has traveled starts, but at the end of the journey has traveled at an average speed for the whole journey.at an average speed for the whole journey.


Constant speedConstant speed

A body traveling at a A body traveling at a constant speed is constant speed is traveling equal traveling equal distances during a distances during a similar time period.similar time period.

This means that the This means that the average speed is the average speed is the same as the same as the instantaneous speed instantaneous speed in this case.in this case.


Velocity is measured as:Velocity is measured as:

VVaverageaverage = distance = distance

time

distance travelled over time taken

D

V T


What are some examples of What are some examples of objects that move at objects that move at highhigh

velocities?velocities?


What are some examples of What are some examples of objects that move at objects that move at lowlow

velocities?velocities?


What units would you use What units would you use to measure the velocity to measure the velocity of an object moving in of an object moving in this classroom?this classroom?

meters per secondmeters per second

m

s or ms-

1

Meters per second tells us how many meters something can move in one second.


GraphingGraphing the Motion of a the Motion of a Particle?Particle?

Distance vs. Time

02468

101214

0 1 2 3 4 5

Time (seconds)

Dis

tan

ce (

met

ers)

Car 1

Car 2

Car 3


ProblemsProblemsA traffic officer finds a car has travelled 600m in 20 A traffic officer finds a car has travelled 600m in 20 seconds. What is the average speed of the carseconds. What is the average speed of the car

Two snails are being raced in a school lab. Eric went Two snails are being raced in a school lab. Eric went 8cm in 24seconds, while splutter went 12cm in 8cm in 24seconds, while splutter went 12cm in 48seconds. Which snail is faster?48seconds. Which snail is faster?

A car is travelling at a constant speed of 30msA car is travelling at a constant speed of 30ms-1. -1. How far How far does it travel in 40secondsdoes it travel in 40seconds

A shock wave from an earthquake travels at a speed of A shock wave from an earthquake travels at a speed of 8kms8kms-1-1.. How long does it take to reach a town 96 km How long does it take to reach a town 96 km away?away?


What else can we know about an What else can we know about an object’s motion besides velocity?object’s motion besides velocity?

What if the object slows down?What if the object slows down?What if the object changes directionWhat if the object changes direction

What if the object’s velocity changes?

•What if the object speeds up?


Scientists have a special way Scientists have a special way to measure a to measure a changechange in in

velocity:velocity:

AccelerationAcceleration


If you’re speeding up, you have If you’re speeding up, you have positive acceleration.positive acceleration.

If you’re slowing down, you have If you’re slowing down, you have negative acceleration.negative acceleration.

If you’re changing speed quickly, you If you’re changing speed quickly, you have high acceleration.have high acceleration.

If you’re changing speed slowly, you If you’re changing speed slowly, you have low acceleration.have low acceleration.

The Way Acceleration Works:


Example:Example:

You’re driving along in You’re driving along in your car and suddenly your car and suddenly have to slam on your have to slam on your brakes for a red light. brakes for a red light. Negative or positive Negative or positive acceleration? High or acceleration? High or low acceleration?low acceleration?

High negative acceleration because you’re slowing down quickly.


You’re an astronaut waiting in You’re an astronaut waiting in your shuttle for takeoff. your shuttle for takeoff. Suddenly the rockets fire Suddenly the rockets fire and you’re on your way to and you’re on your way to Mars. High or low positive Mars. High or low positive or negative acceleration?or negative acceleration?

High positive acceleration because you’re speeding up quickly.

Example:


You’re driving down the You’re driving down the highway when your car runs highway when your car runs out of gas and you slowly out of gas and you slowly roll to a stop on the side of roll to a stop on the side of the road.the road.

Low negative acceleration because you’re slowing down slowly.

Example:


Challenge Question:Challenge Question:

You throw a baseball straight You throw a baseball straight up in the air. It rises to a up in the air. It rises to a certain height and then falls certain height and then falls back to earth, where you back to earth, where you catch it again in your glove.catch it again in your glove.

First, high positive acceleration because it speeds up quickly as it leaves your hand.

Then, as it rises, low negative acceleration, because it begins to slow down slowly because of gravity.

As it begins to fall again, low positive acceleration, because it speeds up slowly.

Finally, when you catch it, high negative acceleration because it slows down very quickly in your hand.


AccelerationAcceleration

Acceleration = change in speedAcceleration = change in speed

change in timechange in time

a = va = v

t t

v

a t


Practice ProblemPractice ProblemAn eagle accelerates from 15 m/s to 22 An eagle accelerates from 15 m/s to 22 m/s in 4 seconds. What is the eagle’s rate m/s in 4 seconds. What is the eagle’s rate of acceleration?of acceleration?

Acceleration = change in speedAcceleration = change in speed

change in timechange in time

Acceleration = Acceleration = 22 m/s - 15 m/s22 m/s - 15 m/s4 s4 s

Acceleration = Acceleration =


ProblemsProblems

A car is moving at 15 msA car is moving at 15 ms-1-1. It then speeds up to 35ms. It then speeds up to 35ms-1-1 in in 40 seconds. What is the acceleration?40 seconds. What is the acceleration?

A toy car moves along a concrete path when its wound A toy car moves along a concrete path when its wound up and let go. The car accelerates from rest to a top up and let go. The car accelerates from rest to a top speed of 6msspeed of 6ms-1-1 in 0.5seconds. What is the acceleration? in 0.5seconds. What is the acceleration?

Find the speed of an object when it accelerates at 4.5msFind the speed of an object when it accelerates at 4.5ms--

22 for 20 seconds for 20 seconds

Find the time taken for an object accelerating at 3 msFind the time taken for an object accelerating at 3 ms-2-2 to to change speed by 12mschange speed by 12ms-1-1


Quick ReviewQuick Review

VelocityVelocity: speed of motion: speed of motion

AccelerationAcceleration: change in velocity: change in velocity

What What causescauses an object’s an object’s velocity to change?velocity to change?


If you’re riding your bike and want to If you’re riding your bike and want to speed up, what do you do?speed up, what do you do?

• If you’re driving a car and want to slow down,

what do you do?

• If you’re playing soccer and want to move the ball,

what do you do?


Pushing pedals, pressing Pushing pedals, pressing brakes, and kicking soccer brakes, and kicking soccer balls are all examples of balls are all examples of

forcesforces..A force is anything thatA force is anything that changes the velocity changes the velocity

of an objectof an object..

But what’s a But what’s a change in velocitychange in velocity??

A change in velocity is A change in velocity is accelerationacceleration, so . . ., so . . .

A force is anything that gives an object A force is anything that gives an object accelerationacceleration..


Nothing will Nothing will change speed change speed (acceleration) unless acted (acceleration) unless acted

upon by a force. If it’s upon by a force. If it’s sitting still, it will keep sitting still, it will keep

sitting still. If it’s moving sitting still. If it’s moving fast, it will keep moving fast, it will keep moving

fast.fast. Only a force can change the

velocity of an object.


Then why do things slow Then why do things slow down?down?

Flying baseballs slow down and eventually Flying baseballs slow down and eventually stop because of the stop because of the force of gravityforce of gravity..

Cars and bikes eventually slow down and Cars and bikes eventually slow down and stop because of the stop because of the force of frictionforce of friction..

Spacecraft in outer space with no friction Spacecraft in outer space with no friction and no gravity will keep going at the same and no gravity will keep going at the same speed forever without a force to slow them speed forever without a force to slow them down or speed them up.down or speed them up.


StarterStarter

What is an object’s speed of motion?What is an object’s speed of motion?

What is a change of an object’s velocity?What is a change of an object’s velocity?

What is the only thing that can change an What is the only thing that can change an object’s velocity and give it acceleration?object’s velocity and give it acceleration?

What affects fast a force can accelerate an What affects fast a force can accelerate an object? object?


Speed – time graphsSpeed – time graphs

A speed-time graph gives information A speed-time graph gives information about acceleration. about acceleration.

Acceleration is the slope of a speed-time Acceleration is the slope of a speed-time graphgraph

The greater the slope of a speed-time The greater the slope of a speed-time graph, the greater the accelerationgraph, the greater the acceleration


Time (s)

Vel

ocity

(m

/s)

0 2 4 6 8 10 12 14 160

5

10

15

20

25

30

More graph – calculate the accelerationat the points indicated.

A

B

C

D

E

F

a= v/t

(5-0)/(2-0)

(10-5)/(6-2)

(20-10)/(8-6)

(25-20)/(12-8)

(25-5)/(14-12)

(5-2)/(16-14)


Finding distanceFinding distance

Speed- time graphs can be used to find Speed- time graphs can be used to find the distance it takes an object to reach a the distance it takes an object to reach a certain speed.certain speed.

This distance is also the area underneath This distance is also the area underneath the slope of the graph.the slope of the graph.


Area under graph = DistanceArea under graph = Distance

Area can be either a triangle or a square Area can be either a triangle or a square or a combinationor a combination

Area of triangle = ½ base x heightArea of triangle = ½ base x height

Area of a square = length x widthArea of a square = length x width


Time (s)

Vel

ocity

(m

/s)

a= v/t

Physics Science AS1.6. NSF North Mississippi GK-8 Topics to be covered Energy Work & Power Heat Motion Forces Momentum Electricity.

Documents

force forces

unbalanced forces

unbalanced force slide

nsf north mississippi

opposite forces

reaction forces

net force

resultant unbalanced