Motion

MotionMotion

GCSE PhysicsGCSE Physics

Book ReferenceBook Reference

Page 66Page 66

Learning IntentionsLearning Intentions

By the end of the lesson we will be able By the end of the lesson we will be able to…to…

o State the difference between State the difference between displacement and distancedisplacement and distance

o Recall the Recall the equationequation for calculating for calculating speedspeed and apply it to solve simple problemsand apply it to solve simple problems

o State the difference between State the difference between speed and speed and velocityvelocity

By definition…By definition…

DistanceDistance (…travelled)- the total length of (…travelled)- the total length of journey taken from start to finish (metre)journey taken from start to finish (metre)

DisplacementDisplacement- a measure of the overall - a measure of the overall change of position, including the direction change of position, including the direction (metre with direction)(metre with direction)

Eg. Distance travelled is 8 metresEg. Distance travelled is 8 metres

Displacement is 4 metres, eastDisplacement is 4 metres, east

2m 2m

4mN

StartStart FinishFinish

QuestionsQuestions

A man drives from Ballymena to A man drives from Ballymena to Coleraine. The 2 towns are 22 miles apart.Coleraine. The 2 towns are 22 miles apart.

a)a) What is the distance travelled?What is the distance travelled?

b)b) What is his displacement?What is his displacement?

c)c) What is his displacement if he turns What is his displacement if he turns around at Coleraine and stops at around at Coleraine and stops at Ballymoney?Ballymoney?

• a) 22 milesa) 22 miles b) 22 miles N b) 22 miles N c) 14 miles c) 14 miles NN

BallymenaBallymena

ColeraineColeraine

BallymoneyBallymoney

8 miles8 miles

DisplacementDisplacement

Extra wee bitExtra wee bitThe displacement of an object after a The displacement of an object after a

journey can be zero-journey can be zero-

The total distance travelled was 50 metresThe total distance travelled was 50 metres

25m

A B

Journey A – B Journey A – B and then B - Aand then B - A

A B

Total displacement from A to Total displacement from A to B and B back to A… zeroB and B back to A… zero

10m

The The raterate at which an object changes the at which an object changes the

distancedistance it has travelled is called its it has travelled is called its speedspeed..

For a complete journey the For a complete journey the speedspeed of an object of an object can be calculated by dividing the can be calculated by dividing the total distancetotal distance covered by the covered by the time takentime taken to complete the to complete the journey-journey-

Average Speed = Total Distance / Time TakenAverage Speed = Total Distance / Time Taken

metres/secondmetres/second == metremetre / second/ second

Ferrari 360 Spider

speed

distance

time

Size direction

This is the quantity given to theThis is the quantity given to the displacement displacement travelled in unit travelled in unit timetime in a given in a given directiondirection

OROR

The rate of change of The rate of change of displacementdisplacement

Velocity is aVelocity is a vector quantity vector quantity

e.g. the bike’s velocity ise.g. the bike’s velocity is 24 m/s 24 m/s EastEast

Lance Armstrong

Scalar versus VectorScalar versus Vector

ScalarsScalars are quantities which are only are quantities which are only described by their sizedescribed by their size

VectorsVectors are quantities which require both are quantities which require both a size and a direction.a size and a direction.

Question TimeQuestion Time

Page 69Page 69

Questions 1-4Questions 1-4 1 mile = 1600 m



o Recall the Recall the equationequation for calculating for calculating accelerationacceleration and apply it to solve simple and apply it to solve simple problemsproblems

o Recognise acceleration as a Recognise acceleration as a vector vector quantityquantity

Which object has the greatest Which object has the greatest Acceleration?Acceleration?

Snap ShotsSnap Shots

Constant VelocityConstant Velocity

Changing VelocityChanging Velocity

Disp

Disp.

The average acceleration of an object is The average acceleration of an object is given by the change in velocity per unit given by the change in velocity per unit time-time-

Acceleration = Change in Velocity / Time Taken

Acceleration = (Final Velocity – Initial Velocity) / Time Taken

a = (v – u) / t

m/s2 = m/s / sa t

Δv

Usain Bolt’s AccelerationUsain Bolt’s Acceleration

Work out Usain’s change in motion duringWork out Usain’s change in motion during– first 30 metresfirst 30 metres

– last 20 metreslast 20 metres

Wee bit extraWee bit extra

AccelerationAcceleration is a is a vectorvector quantity. It quantity. It can be a positive or negative value.can be a positive or negative value.

When an object’s initial velocity is greater When an object’s initial velocity is greater than the final velocity then it is said to be than the final velocity then it is said to be slowing downslowing down or or deceleratingdecelerating (negative (negative

acceleration)acceleration)

ExamplesExamples

Example AExample A

Acceleration = change in velocity / time takenAcceleration = change in velocity / time taken

= (8 – 0) / 4= (8 – 0) / 4

= 8 / 4 = = 8 / 4 = 2 m/s2 m/s22

Example BExample B

aa = = Δv / t

= (0 – (-8)) / 4

= 8 / 4 = 2 m/s2

Complete the Chart showing steady Complete the Chart showing steady accelerationacceleration

All Velocities are in m/sAll Velocities are in m/s

Calculate the accelerations of X and YCalculate the accelerations of X and Y

What is special about the acceleration of What is special about the acceleration of X? Explain it’s journey…X? Explain it’s journey…

TimeTime 11 22 33 44 55 66

Velocity XVelocity X - 2.0- 2.0 0.00.0 2.02.0 6.06.0

Velocity YVelocity Y 17.517.5 15.015.0 12.512.5 7.57.5

4.0 8.0

X = 2 m/s2

Y = -2.5 m/s2

10.0 5.0

Homework QuestionsHomework Questions

Page 70, Qs 5 - 8Page 70, Qs 5 - 8

Vectors and ScalarsVectors and Scalars

Spot the Spot the vectorsvectors among the among the scalarsscalars

5 m/s

16 m due North

- 17 m/s216 Newtons

7 N

67 m/s

12 seconds

94 Joules



o Construct a Construct a distance-time graphdistance-time graph to to represent motionrepresent motion

o Identify Identify common shapescommon shapes of a d-t graph of a d-t grapho Use a d-t graph to calculate an Use a d-t graph to calculate an unknown unknown

speedspeed

Distance – Time GraphsDistance – Time Graphs

This is a visual way of representing motion This is a visual way of representing motion by using a graph.by using a graph.

Usain Bolt, Berlin, 100m World Record

0

10

20

30

40

50

60

70

80

90

100

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00

Time (second)

Dis

tan

ce

(m

etr

e)

Dis

tan

ce (m

)

Dist.

Straight line, positive correlation, both increase at the same rate

Dis

tan

ce (m

)

Dist.

Curves up, as seconds pass, the car covers more distance than the second before

Distance -Time graph (Pg 71)Distance -Time graph (Pg 71)

Some of the common shapes that describe Some of the common shapes that describe the motion of an object are-the motion of an object are-

speed speed speed

Increasing speed

Decreasing speed

in CCEAPage 73 in CCEA

Question 10 (answer in full!)Question 10 (answer in full!)



o Identify Identify common shapescommon shapes of a d-t graph of a d-t grapho Use a d-t graph to calculate an Use a d-t graph to calculate an unknown unknown

speedspeedo Recognise the link between the Recognise the link between the gradientgradient of of

a d-t graph for an object and the a d-t graph for an object and the motionmotion of of that objectthat object

The word The word ‘gradient’‘gradient’ is used to explain the is used to explain the shape of the line on the graphshape of the line on the graph

• Match the phrases to the correct graphsMatch the phrases to the correct graphs

A A valuevalue for the gradient of a graph can be for the gradient of a graph can be calculated by dividing the calculated by dividing the change in the ‘y change in the ‘y value’value’ by the by the change in the ‘x value’change in the ‘x value’

0 15

75

y

x1.2

4.8

y

x0

Gradient = 75 / 15

= 5

Gradient = -4.8 / 1.2

= -4Negative gradient,

slope down

Distance / Time graph for car

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30 35 40 45 50 55

Time / seconds

Dis

tan

ce /

me

tre

s

The change in y is the distance the object has travelled

The change in x is the time the object was travelling

Speed equals distance divided by time, therefore the gradient of the graph is the same as the speed of the object

What is the gradient, and hence the speed of

the car?

Distance / Time graph for car

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30 35 40 45 50 55

Time / seconds

Dis

tan

ce /

me

tre

s

Change in y = Distance travelled

= 800 – 200 = 600 m

Change in x = Time taken

= 36 - 16 = 20 s

Gradient = Speed = Distance / Time

= 600 / 20 = 30 m/s



o Identify Identify common shapescommon shapes of a v-t graph of a v-t grapho Use a v-t graph to calculate an Use a v-t graph to calculate an unknown unknown

accelerationaccelerationo Recognise the link between the Recognise the link between the gradientgradient of of

a v-t graph for an object and the a v-t graph for an object and the motionmotion of of that objectthat object

We’ve seen how We’ve seen how Distance-TimeDistance-Time graphs graphs can be a clear illustration of an object’s can be a clear illustration of an object’s motion. Another usefully way to present motion. Another usefully way to present this motion is in the form of a this motion is in the form of a Velocity- Velocity- Time graph.Time graph.

Felix is bonkers…

Felix's Jump

0

10

20

30

40

50

60

0 5 10 15 20 25 30

Time (s)

Velo

cit

y (

m/s

)

Velocity -Time graphVelocity -Time graph

Some of the common shapes that describe Some of the common shapes that describe the motion of an object are-the motion of an object are-

speed speed speed

Increasing speed

Decreasing speed

Acceleration Constant speed

Slower Acceleration StoppedDeceleration

v v v

v v v

t t

t

t

Slower constant speed

For a For a Distance-TimeDistance-Time Graph the gradient Graph the gradient at any instant represents the at any instant represents the speedspeed

- eg. Zero (flat) gradient means no speed- eg. Zero (flat) gradient means no speed

For a For a Velocity-TimeVelocity-Time Graph, the gradient Graph, the gradient at any instant represents the at any instant represents the accelerationacceleration

- eg. Steep (high) gradient means large - eg. Steep (high) gradient means large accelerationacceleration



o Calculate Calculate displacementdisplacement from a v-t graph from a v-t grapho Recall what is meant by an object’s Recall what is meant by an object’s

momentummomentumo State the State the equationequation for momentum and for momentum and

solve simple problems related to solve simple problems related to momentummomentum

Time (s)Time (s)

Vel

oci

ty (

m/s

)V

elo

city

(m

/s)

4

10

Consider this example- A car travels at 4 Consider this example- A car travels at 4 m/s for 10 sm/s for 10 sVelocity / Time graph for the motionVelocity / Time graph for the motion

Time (s)Time (s)

Vel

oci

ty (

m/s

)V

elo

city

(m

/s)

4

10

Velocity = Displacement / TimeVelocity = Displacement / Time

Area under the graph!!

From the graph-

Velocity = 4 m/s Time = 10 s

Re-arrange the equation- d = v x t

= 4 x 10 = 40 m

v

d

t

For a For a Velocity-TimeVelocity-Time graph the graph the displacementdisplacement can be calculated by finding can be calculated by finding the the area under the linearea under the line

What is the total displacement of each of What is the total displacement of each of the object’s motion illustrated in the graphs the object’s motion illustrated in the graphs below-below-

tt

VV

15

200tt

VV

5

168

Area under line = 15 x 200

Displacement = 3000 m

Area under line = (5 x 8) + (0.5 x 8 x 5)

Displacement = 60 m

Try this one…Try this one…

Pg 74Pg 74

Questions 13 (Ignore the last sentence in Questions 13 (Ignore the last sentence in Q13 about the ‘graphical method’)Q13 about the ‘graphical method’)

MomentumMomentum

The Superhero factor!The Superhero factor!

MomentumMomentum

If an object is If an object is movingmoving then it has momentum. then it has momentum. This can be calculated by using the equation-This can be calculated by using the equation-

Momentum = Mass x VelocityMomentum = Mass x Velocity

p = m x vp = m x v

kgm/s = kg x m/skgm/s = kg x m/s

Momentum is a Momentum is a vectorvector quantity quantity

ExampleExample

What is the momentum of i) the car, ii) the What is the momentum of i) the car, ii) the motorcycle?motorcycle?Which would have more momentum if they Which would have more momentum if they were both travelling at the same velocity, were both travelling at the same velocity, why?why?

Mass (kg)Mass (kg) Velocity Velocity (m/s)(m/s)

CarCar 10001000 55

MotorcycleMotorcycle 200200 3030

Momentum = mass x velocityMomentum = mass x velocity p = m x vp = m x v- For the car- For the carp = 1000 x 5 = 5000 kgm/sp = 1000 x 5 = 5000 kgm/s- For the motorcycle- For the motorcyclep = 200 x 30 = 6000 kgm/sp = 200 x 30 = 6000 kgm/s

If they were both travelling at the same speed the car If they were both travelling at the same speed the car would have the most momentum as it has the most would have the most momentum as it has the most massmass

Mass (kg)Mass (kg) Velocity Velocity (m/s)(m/s)

CarCar 10001000 55

MotorcycleMotorcycle 200200 3030

Motion

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Transcript of Motion