FORCE & MOTION. OBSERVATION Observations · Pay close attention to the following. · Make notes on what you observe. · Do not take anything for granted.

FORCE & MOTION

Motion• Observing a displacement of one thing relative

to another.

• Describing Motion

• All motion is Relative

• The object moved in relation to the reference object

or point.

Frame of Reference

• The context or limits of what we are discussing• Helps us have a common scope for discussion

Measurement• Defines a scaled common reference

• Can be replicated

• Is known and referenced

• Quantifies the change in position

• Common measurement scales are:• Standard (English/US)

• Feet, Pounds, etc.• Metric

• Meters, Grams, Liters• Internationally accepted system (SI)

LINEAR MOTIONConcepts: Scalars & Vectors

How Do We Describe “Where”?

• If objects move, how can we describe…– How far?– How much?– What direction?

• “How much” or “How far” is the magnitude of motion

• “What direction” is the direction of motion.

Two different “How Far’s”

• Distance– How far?– Scalar– Only measures path

• Displacement– How far from the start are we now?– What direction is it from the start to finish?– Vector– Measure distance and direction from start point to end

point.

Scalars: Magnitude or Direction

MagnitudeHow big

How much

What quantity

OR

DirectionCardinalDegree

Distance: A Scalar

Distance

Start

Finish

Vectors: Magnitude & Direction

MagnitudeHow big

How much

What quantity

AND

DirectionCardinalDegree

Displacement: A VectorDisplacement Finish

Start

Vector Addition“Connect the dots”

Vector Addition

• “Add” vectors to find the net result of the trip.• Net Displacement: The sum of the vectors

Start

Finish

Net Displacement Vector

Finding “Net Displacement” Using Math

• Add all Vertical vectors• Add all horizontal vectors• Us Pythagorean Theorem

Start

Finish

Net Displacement Vector

Start

Finish

Net Displacement Vector

Sum of vertical vectors

Sum of horizontal vectors

Net Displacementa2

a

b

b2

c2

RATESSpeed, Velocity, Acceleration

Vectors Are Found Throughout Physics

• There are three basic measureable properties in science– Mass– Distance– Time

• Physicists use these to describe the relationships and properties of an objects and their motions.

Speed• Ratio of distance travelled to time taken

• Distance ÷ Time• Scalar quantity

• No direction• Path is important

Velocity• Ratio of displacement to time taken

• Displacement ÷ Time• Vector quantity• Measured from start point to end point• Disregards path

Comparing Speed and Velocity

Dist. = 24 metersTime = 12 secondsSpeed = 2 m/s

Comparing Speed and Velocity

Disp. = 9 meters ENETime = 3 secondsVelocity = 3 m/s ENE

Science Problems“What’s your problem with problems?”

Speedy Velocity Problems“How to work science problems”

Jimmy the Frog hops around his pond.

His hop-o-meter says he has travelled

36 meters. The sundial says it only

took him 20 minutes.

• What was Jimmy’s speed?

How to work science problems

Step 1: Identify your variables (with units!)Jimmy the Frog hops around his pond. His hop-o-meter says he has travelled 36 meters. The sundial says it only took him 20 minutes.

• What was Jimmy’s speed?

Distance: 36 metersTime: 20 minutes

Speed: ???

Distance:36 metersTime: 20 minutesSpeed: ???

How to work science problems

Step 2: Write down the equation

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

Distance:36 metersTime: 20 minutesSpeed: ???

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

How to work science problems

Step 3: Change the equation to find the missing variable

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

SpeedWhat do I need to find?

No

What does the equation solve for?

Do I need to change the equation?

Speed

Distance:36 metersTime: 20 minutesSpeed: ???

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

How to work science problems

Step 4: Substitute variable values into formula.

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=36𝑚20𝑚𝑖𝑛 .

Distance:36 metersTime: 20 minutesSpeed: ???

Distance:36 metersTime: 20 minutesSpeed: ???

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=36𝑚20𝑚𝑖𝑛 .

How to work science problems

Step 5: Do (and show!!!) your work

𝑆𝑝𝑒𝑒𝑑=36𝑚20𝑚𝑖𝑛 .

=

Distance:36 metersTime: 20 minutesSpeed: ???

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=36𝑚20𝑚𝑖𝑛 .

=

How to work science problems

Step 6: Identify your answer

Speed = 1.8 m/min.

Distance:36 metersTime: 20 minutesSpeed: ???

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=36𝑚20𝑚𝑖𝑛 .

=

Speed = 1.8 m/min.

Distance:36 metersTime: 20 minutesSpeed: ???

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑡𝑖𝑚𝑒

𝑆𝑝𝑒𝑒𝑑=36𝑚20𝑚𝑖𝑛 .

=

Speed = 1.8 m/min.

ACCELERATIONIt’s all about change

Acceleration· Ratio of change in velocity to time

· (Displacement ÷ Time) ÷ Time

· Vector quantity

· A change in velocity (direction or magnitude) constitutes

acceleration

GRAPHING MOTION

Dis

tanc

eDistance/Time or Speed Graphs

Speed3.5

3

2.5

(m)

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Distance/Time or Speed GraphsSpeed

3.5

3

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Dis

tanc

e(m

)

Distance/Time or Speed GraphsSpeed

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Dis

tanc

e(m

)

Distance/Time or Speed GraphsSpeed

12

10

8

6

Object 14

2

01 2 3 4 5

Time (s)

Dis

tanc

e(m

)

Displacement/Time or Velocity GraphsVelocity

3.5

3

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Dis

plac

emen

t(m

)

Displacement/Time or Velocity GraphsVelocity

1.2

1

0.8

0.6

Object 10.4

0.2

01 2 3 4

Time (s)

(m)

Dis

plac

emen

t

Displacement/Time or Velocity GraphsVelocity

3.5

3

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

(m)

Dis

plac

emen

t

Displacement/Time or Velocity GraphsVelocity

14

12

10

8

6

4

2

0

Object 1

1 2 3 4 5 6Time (s)

(m)

Dis

plac

emen

t

Vel

ocity

(m

/s)

Velocity/Time (Acceleration) GraphsAcceleration

3.5

3

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Velocity/Time (Acceleration) GraphsAcceleration

2.5

2

1.5

1

0.5

0

Object 1

1 2 3 4Time (s)

Vel

ocity

(m

/s)

Momentum

Physical Properties of Objects

Innate Properties• Mass• Speed• Size• Density• Color

Derived Properties• Density• Speed• Weight

Observations on Objects in Motion

• Move in a straight line– Unless something pushes them off that line

• Speed wants to remains constant– Less friction is less loss of “speed”

• Massive objects are harder to move– Need more push to move

Observations on Objects in Motion

• If a moving object hits a non-moving object, the non-moving object is set in motion and the speed of the first moving object is reduced.

• How?• Is there a relationship of properties that may

explain this?

Observations on Objects in Motion

What properties of objects seem to be involved?• Speed • MassWhat should we call this Speed-Mass property?• Momentum

𝑀𝑎𝑠𝑠×𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦=𝑀𝑜𝑚𝑒𝑛𝑡𝑢𝑚

Objects & Momentum

𝑀𝑎𝑠𝑠×𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦=𝑀𝑜𝑚𝑒𝑛𝑡𝑢𝑚

Newton’s Laws

Newton’s First Law

• An object will retain it motion unless an outside force acts upon it.

• Inertia: The resistance to movement of an object relative to its mass.

Newton’s Second Law

• An object will accelerate if an unbalanced force is applied to it.

𝑭𝒐𝒓𝒄𝒆=𝒎𝒂𝒔𝒔×𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏

𝑭=𝒎×𝒂

Newton’s Third Law

• All forces between two objects exist in equal magnitude and opposite direction

Weight of Object

Normal Force of Object

END OF MOTIONLECTURE