OCR Gateway Additional Science

1
P3 Forces for Transport
OCR Gateway Additional Science
W Richards The Weald School
2
P3a Speed
3
Distance, Speed and Time
03/03/2015
03/03/2015

1. Freddie walks 200 metres in 40 seconds. What is
   his speed?
2. Hayley covers 2km in 1,000 seconds. What is her
   speed?
3. How long would it take Lauren to run 100 metres
   if she runs at 10m/s?
4. Jake travels at 50m/s for 20s. How far does he
   go?
5. Izzy drives her car at 85mph (about 40m/s). How
   long does it take her to drive 20km?

5m/s
2m/s
10s
1000m
500s
4
Distance, Speed and Time
03/03/2015
03/03/2015

1. Sarah walks 2000m in 50 minutes. What is her
   speed in m/s?
2. Jack tries to walk the same distance at a speed
   of 5m/s. How long does he take?
3. James drives at 60mph (about 100km/h) for 3
   hours. How far has he gone?
4. The speed of sound in air is 330m/s. Molly
   shouts at a mountain and hears the echo 3 seconds
   later. How far away is the mountain? (Careful!)

0.67m/s
400s
300km
495m
5
How speed cameras work
Speed cameras work by recording the position of
the car at a certain time apart. What is the
speed of the trolley in the lab example done
below?
6
Average Speed
It is common to see average speed cameras near
roadworks. They work by recording how long you
take to cover a certain distance and then working
out your average speed.

1. Two cameras are 1km apart and a car takes 50s to
   travel between them. What was the cars average
   speed?
2. A car accelerates from 10 to 20m/s for 50s. How
   far has it gone?
3. How long would it take to travel 10km if you
   started at a speed of 30m/s and ended up at 50m/s
   after the 10km?

20m/s
750m
250s
7
Distance-time graphs
40 30 20 10 0




Distance (metres)
Time/s
20 40 60 80 100
8
40 30 20 10 0




Distance (metres)
Time/s
20 40 60 80 100

1. What is the speed during the first 20 seconds?
2. How far is the object from the start after 60
   seconds?
3. What is the speed during the last 40 seconds?
4. When was the object travelling the fastest?

9
Distance-time graph for non-uniform motion
40 30 20 10 0




Distance (metres)
Time/s
20 40 60 80 100
10
03/03/2015
40 30 20 10 0
03/03/2015




Distance (metres)
Time/s
20 40 60 80 100
1.5m/s

1. What was the velocity in the first 20 seconds?
2. What was the velocity between 20 and 40 seconds?
3. When was this person travelling the fastest?
4. What was the average speed for the first 40
   seconds?

0.5m/s
80-100s
1m/s
11
P3b Changing Speed
12
Acceleration
03/03/2015
03/03/2015

1. A cyclist accelerates from 0 to 10m/s in 5
   seconds. What is her acceleration?
2. A ball is dropped and accelerates downwards at a
   rate of 10m/s2 for 12 seconds. How much will the
   balls velocity increase by?
3. A car accelerates from 10 to 20m/s with an
   acceleration of 2m/s2. How long did this take?
4. A rocket accelerates from 1,000m/s to 5,000m/s in
   2 seconds. What is its acceleration?

2m/s2
120m/s
5s
2000m/s2
13
Speed-time graphs
80 60 40 20 0




Velocity m/s
T/s
10 20 30 40 50
14
03/03/2015
03/03/2015
80 60 40 20 0




Velocity m/s
T/s
10 20 30 40 50

1. How fast was the object going after 10 seconds?
2. What is the acceleration from 20 to 30 seconds?
3. What was the deceleration from 30 to 50s?
4. How far did the object travel altogether?

40m/s
2m/s2
3m/s2
1700m
15
Speed-time graph for non-uniform motion
40 30 20 10 0




Distance (metres)
Time/s
20 40 60 80 100
16
03/03/2015
03/03/2015
80 60 40 20 0




Velocity m/s
T/s
10 20 30 40 50

1. How fast was the object going after 10 seconds?
2. What is the acceleration from 20 to 30 seconds?
3. What was the deceleration from 40 to 50s?
4. How far did the object travel altogether?

10m/s
4m/s2
6m/s2
1500m
17
03/03/2015
03/03/2015
80 60 40 20 0




Velocity m/s
T/s
10 20 30 40 50
This velocity-time graph shows Coryns journey to
school. How far away does she live?
2500m
18
Speed vs. Velocity
03/03/2015
03/03/2015
Speed is simply how fast you are travelling
Velocity is speed in a given direction
19
Circular Motion
03/03/2015
03/03/2015
1) Is this car travelling at constant speed? 2)
Is this car travelling at constant velocity?
20
P3c Forces and Motion
21
Force and acceleration
03/03/2015
03/03/2015
If the forces acting on an object are unbalanced
then the object will accelerate, like these
wrestlers
Force (in N) Mass (in kg) x Acceleration (in
m/s2)
22
Force, mass and acceleration
03/03/2015
03/03/2015

1. A force of 1000N is applied to push a mass of
   500kg. How quickly does it accelerate?
2. A force of 3000N acts on a car to make it
   accelerate by 1.5m/s2. How heavy is the car?
3. A car accelerates at a rate of 5m/s2. If it
   weighs 500kg how much driving force is the engine
   applying?
4. A force of 10N is applied by a boy while lifting
   a 20kg mass. How much does it accelerate by?

2m/s2
2000kg
2500N
0.5m/s2
23
Stopping a car
03/03/2015
03/03/2015
What two things must the driver of the car do in
order to stop in time?
24
Stopping a car
03/03/2015
03/03/2015
Too much alcohol
Tiredness
Too many drugs
Poor visibility
Wet roads
Icy roads
Tyres/brakes worn out
Driving too fast
Total Stopping Distance Thinking Distance
Braking Distance
25
Stopping Distances
This diagram (taken from drivingtestsuccess.com)
shows the thinking and braking distances for
different speeds. What patterns do you notice?
Thinking distance increases linearly
Braking distance increases in a squared
relationship
26
P3d Work and Power
27
Weight vs. Mass
03/03/2015
03/03/2015
Earths Gravitational Field Strength is 10N/kg.
In other words, a 1kg mass is pulled downwards by
a force of 10N.
Weight Mass x Gravitational Field Strength (in
N) (in kg) (in N/kg)
20N

1. What is the weight on Earth of a book with mass
   2kg?
2. What is the weight on Earth of an apple with mass
   100g?
3. James weighs 700N on the Earth. What is his
   mass?
4. On the moon the gravitational field strength is
   1.6N/kg. What will James weigh if he stands on
   the moon?

1N
70kg
112N
28
Work done
03/03/2015
03/03/2015
When any object is moved around work will need to
be done on it to get it to move (obviously).
We can work out the amount of work done in
moving an object using the formula
Work done Force x distance moved in J
in N in m
29
Example questions
03/03/2015
03/03/2015

1. Jessie pushes a book 5m along the table with a
   force of 5N. She gets tired and decides to call
   it a day. How much work did she do?
2. Hayley lifts a laptop 2m into the air with a
   force of 10N. How much work does she do? What
   type of energy did the laptop gain?
3. James does 200J of work by pushing a wheelbarrow
   with a force of 50N. How far did he push it?
   What type of energy did the wheelbarrow gain?
4. Jack cuddles his cat and lifts it 1.5m in the
   air. If he did 75J of work how much force did he
   use?
5. Freddie drives his car 1000m. If the engine was
   producing a driving force of 2000N how much work
   did the car do?

25J
20J, GPE
4m, KE
50N
2MJ
30
A Practical Example of Doing Work
03/03/2015
Consider a rocket re-entering the Earths
atmosphere
The rocket would initially have a very high
_______ energy. This energy would then _____ due
to friction caused by collisions with _______ in
the atmosphere. These collisions would cause the
rocket to ____ up (_____ is being done on the
rocket). To help deal with this, rockets have
special materials that are designed to lose heat
quickly.
Words work, kinetic, particles, heat, decrease
31
Energy and Power
03/03/2015
The POWER RATING of an appliance is simply how
much energy it uses every second. In other
words, 1 Watt 1 Joule per second
E Energy (in joules) P Power (in watts) T
Time (in seconds)
32
Some example questions
03/03/2015

1. What is the power rating of a light bulb that
   transfers 120 joules of energy in 2 seconds?
2. What is the power of an electric fire that
   transfers 10,000J of energy in 5 seconds?
3. Tanner runs up the stairs in 5 seconds. If he
   transfers 1,000,000J of energy in this time what
   is his power rating?
4. How much energy does a 150W light bulb transfer
   in a) one second, b) one minute?
5. Pierres brain needs energy supplied to it at a
   rate of 40W. How much energy does it need during
   a 50 minute physics lesson?
6. Levis brain, being more intelligent, only needs
   energy at a rate of about 20W. How much energy
   would his brain use in a normal day?

60W
2KW
0.2MW
150J, 9KJ
120KJ
1.73MJ
33
An example with cars
What are the advantages and disadvantages of each
car?
34
Power
03/03/2015
Power (in watts) is the rate of doing work
35
Random questions on work and power
03/03/2015

1. Jordan pushes Tom in the direction of a cliff.
   If he uses a force of 40N and he moves Tom 10m in
   4s calculate the work done and Jordans power
   rating.
2. Chris runs up some stairs and has a power rating
   of 600W while he does so. If he does it in 5
   seconds and his weight is 750N calculate how high
   the stairs are.
3. A man pulls a block of wood and uses a force of
   50N. If the distance travelled horizontally is
   5m calculate the work done by the man and his
   power if the journey lasted 10 seconds.

400J, 100W
4m
250J, 25W
36
P3e Energy on the Move
37
Kinetic energy
03/03/2015
03/03/2015
Any object that moves will have kinetic
energy. The amount of kinetic energy an object
has can be found using the formula
Kinetic energy ½ x mass x velocity squared in J
in kg in m/s
KE ½ mv2
38
Example questions
03/03/2015
03/03/2015

1. Shannon drives her car at a speed of 30m/s. If
   the combined mass of her and the car is 1000kg
   what is her kinetic energy?
2. Issy rides her bike at a speed of 10m/s. If the
   combined mass of Issy and her bike is 80kg what
   is her kinetic energy?
3. Will is running and has a kinetic energy of 750J.
   If his mass is 60kg how fast is he running?
4. Josh is walking to town. If he has a kinetic
   energy of 150J and hes walking at a pace of 2m/s
   what is his mass?

450,000J
4000J
5m/s
75kg
39
Stopping Distances revision
Recall the patterns we observed in this data
Thinking distance increases linearly
Braking distance increases in a squared
relationship
40
Stopping a car
03/03/2015
03/03/2015
What happens inside the car when it stops?
In order to stop this car the brakes must do
work. This work is used to reduce the kinetic
energy of the vehicle and the brakes will warm up
this is why the braking distance depends on
speed2
41
An example question
03/03/2015
03/03/2015
This car can apply a maximum braking force of
10,000N. If the cars mass is 1000Kg how far is
its stopping distance when it is travelling at a
speed of 15m/s (roughly 30mph) and 30m/s (roughly
60mph)?
15m/s 11.25m stopping distance 30m/s 45m
stopping distance (4 times greater)
42
Different ways of fuelling cars
What are the advantages and disadvantages of each
of the following fuels?
43
Fuel consumption
How do the following features help or hinder fuel
economy?
44
P3f Crumple Zones
45
Momentum
03/03/2015
03/03/2015
Any object that has both mass and velocity has
MOMENTUM. Momentum (symbol p) is simply given
by the formula

• What is the momentum of the following?
• A 1kg football travelling at 10m/s
• A 1000kg Ford Capri travelling at 30m/s
• A 20g pen being thrown across the room at 5m/s
• A 70kg bungi-jumper falling at 40m/s

10kgm/s
30,000kgm/s
0.1kgm/s
2800kgm/s
46
Force and momentum
Newtons second law of motion says that the force
acting on an object is that objects rate of
change of momentum. In other words

• For example, Rooney takes a free kick by kicking
  a stationary football with a force of 40N. If
  the ball has a mass of 0.5kg and his foot is in
  contact with the ball for 0.1s calculate
• The change in momentum of the ball (its impulse),
• The speed the ball moves away with

47
Example questions
03/03/2015

1. Paddy likes playing golf. He strikes a golf ball
   with a force of 80N. If the ball has a mass of
   200g and the club is in contact with it for 0.2s
   calculate a) the change in momentum of the golf
   ball, b) its speed.
2. Courtney thinks its funny to hit tennis balls at
   Kit. She strikes a serve with a force of 30N.
   If the ball has a mass of 250g and the racket is
   in contact with it for 0.15s calculate the balls
   change in momentum and its speed.
3. Tom takes a dropkick by kicking a 0.4kg rugby
   ball away at 10m/s. If his foot was in contact
   with the ball for 0.1 seconds calculate the force
   he applied to the ball.
4. Jenny strikes a 200g golf ball away at 50m/s. If
   she applied a force of 50N calculate how long her
   club was in contact with the ball for.

16Kgm/s, 80m/s
4.5Kgm/s, 18m/s
40N
0.2s
48
Safety features
03/03/2015
03/03/2015
How do air bags and crumple zones work?

• Basically
• The change in momentum is the same with or
  without an airbag
• But having an airbag increases the time of the
  collision
• Therefore the force is reduced

49
Car Safety Features
These objects all help reduce injury by basically
absorbing energy.
Cars also have ABS brakes which prevent them from
skidding by automatically pumping off and on to
avoid the brakes locking.
50
P3g Falling Safely
51
Introduction to Forces
03/03/2015
A force is a push or a pull. Some common
examples
Air resistance/drag a contact force that acts
against anything moving through air or liquid
Weight (mg) pulls things towards the centre of
the Earth
Friction a contact force that acts against
anything moving
Upthrust keeps things afloat
52
Examples of Air Resistance
53
Balanced and unbalanced forces
03/03/2015
03/03/2015
Reaction
Consider a camel standing on a road. What forces
are acting on it?
These two forces would be equal we say that
they are BALANCED. The camel doesnt move
anywhere.
Weight
54
Balanced and unbalanced forces
03/03/2015
03/03/2015
Reaction
What would happen if we took the road away?
Weight
55
Balanced and unbalanced forces
03/03/2015
03/03/2015
56
Balanced and unbalanced forces
03/03/2015
03/03/2015
1) This animal is either ________ or moving with
_______ _____
2) This animal is getting ________
4) This animal is also either _______ or moving
with ________ ______..
3) This animal is getting _______.
Words - Stationary, faster, slower or constant
speed?
57
03/03/2015
03/03/2015
Summary
Complete these sentences
If an object is stationary and has NO resultant
force on it the object will If an object is
stationary and a resultant force acts on it the
object will If an object is already moving and
NO resultant force acts on it the object
will If an object is already moving and a
resultant force acts on it the object will
continue to move at the same speed and the same
direction
accelerate in the direction of the resultant
force
continue to stay stationary
accelerate in the direction of the resultant
force
58
Terminal Speed
Consider a skydiver

1. At the start of his jump the air resistance is
   _______ so he _______ downwards.

2) As his speed increases his air resistance will
_______
3) Eventually the air resistance will be big
enough to _______ the skydivers weight. At this
point the forces are balanced so his speed
becomes ________ - this is called TERMINAL SPEED
Words increase, small, constant, balance,
accelerates
59
Terminal Speed
Consider a skydiver

• 4) When he opens his parachute the air
  resistance suddenly ________, causing him to
  start _____ ____.

5) Because he is slowing down his air resistance
will _______ again until it balances his
_________. The skydiver has now reached a new,
lower ________ _______.
Words slowing down, decrease, increases,
terminal speed, weight
60
Velocity-time graph for terminal velocity
Velocity




Time
61
Acceleration due to Gravity
Notice that the skydivers weight didnt change
at any point. Or did it?
In reality, every object that is close to the
_____ has the same gravitational _______.
However, if you drop an object from the top of Mt
Everest its acceleration will be slightly ______!
Also, if you take out __ ______, objects would
fall with the same acceleration (like the
skydiver on the _____).
Words acceleration, Earth, moon, air
resistance, smaller
62
P3h The Energy of Games and Theme rides
63
Gravitational Potential Energy
03/03/2015
To work out how much gravitational potential
energy (GPE) an object gains when it is lifted up
we would use the simple equation
GPE Mass x Acceleration of free-fall x Change
in height
(Joules) (newtons) (10N/kg)
(metres)
(Remember - Wmg)
64
Some example questions
03/03/2015

• How much gravitational potential energy have the
  following objects gained?
• A brick that weighs 10N lifted to the top of a
  house (10m),
• A 1,000kg car lifted by a ramp up to a height of
  2m,
• A 70kg person lifted up 50cm by a friend.
• How much GPE have the following objects lost?
• A 2N football dropping out of the air after being
  kicked up 30m,
• A 0.5N egg falling 10m out of a bird nest,
• A 1,000kg car falling off its 200cm ramp.

100J
20KJ
350J
60J
5J
20KJ
65
Energy changes for a skydiver
Recall our skydiver

• If the skydiver has reached terminal speed
  explain what happens to his
• Kinetic energy
• Gravitational potential energy
• while he is falling.

66
Understanding Kinetic Energy
KE ½ mv2
67
Roller Coasters
1) Electrical energy is transferred into
gravitational potential energy
3) Kinetic energy is transferred back into
gravitational potential energy
2) Gravitational potential energy is transferred
into kinetic energy
68
Using conservation of energy when dropping objects
If I drop this ball 1m how fast will it be going
when it hits the floor?
Use GPE at top Kinetic energy at bottom
mgh ½mv2
gh ½v2
v2 2 x 10 x 1
v2 20
v 4.5m/s
69
An example question
03/03/2015
If the height of the drop was 100m and assuming
there was a 100 conversion from gravitational to
kinetic energy, how fast was the roller coaster
car moving at the bottom of the ramp?