1. 9K Speeding up
9K Speeding up
How fast?
Speed and forces
Slow down!

2. 9K Speeding up
How fast?

3. Match each animal to its top speed. What do we mean by speed?
9K Look at it go!
Match each animal to its top speed.
800 km/h
350 km/h
110 km/h
0.005 km/h
What do we mean by speed?
peregrine falcon in a dive
earthworm in a hurry
sailfish in the seas around Florida
cheetah over short distances
tortoise in a jet plane (in first class)
350 km/h
110 km/h
800 km/h
110 km/h
0.005 km/h

4. How did people work out the speeds of the animals?
9K Calculating speed
distance
time
speed =
How did people work out the speeds of the animals?
You need to know the distance travelled and the time it took to travel that distance.
What’s the earthworm’s speed? (Don’t forget the units!)

5. A formula triangle makes it easy to remember and use the formula:
9K Speedy formula work
distance
speed =
time
A formula triangle makes it easy to remember and use the formula:
distance = speed  time
distance
time
speed =
distance
time =
speed

6. A train takes 90 minutes to get from Leicester to London.
9K How far?
A train takes 90 minutes to get from Leicester to London.
Its average speed is 70 km/h.
What is the distance between London and Leicester?
distance = speed  time
= 70 km/h  1.5 h
= 105 km
Why is the time measured in hours and not minutes?

7. Convert the time from seconds to hours
9K Changing the units
A cheetah runs for 4 seconds and catches a daydreaming zebra. The cheetah runs at 100 km/h. How far away was the zebra?
distance = speed  time 4
60  60
= 100 km/h  h
= 0.11 km
Convert the time from seconds to hours
How far is this in metres? (Not far enough for the zebra!)
Why did we convert the time from seconds to hours?

8. The speed limit is 45 km/h. Who was speeding?
9K Who’s speeding?
A speed camera takes a picture, then another one 1 second later. The distance travelled gives the speed of the cars passing the camera.
The speed limit is 45 km/h. Who was speeding?
driver
distance travelled
speed
Major Bump
May Crash
Mrs Byinches
15 m
12 m
16 m
Think about the units!
54 km/h
43.2 km/h
57.6 km/h

9. They have to walk there and back!
9K When?
Some walkers are walking up Yr Wyddfa (Snowdon). It is 7 km to the top.
It’s steep in parts, so they walk about 1.5 km every hour.
It will start getting dark in 4 hours’ time.
Should they try to get to the summit and back or wait until tomorrow?
time =
distance
speed
They have to walk there and back! =
14 km
1.5 km/h
= 9.3 h
What would you do?

10. 1. To work out Joel’s speed in a race, you need to know:
9K Quick quiz
1. To work out Joel’s speed in a race, you need to know:
a) the distance he ran and the time he took
b) the distance he ran and the position he finished in
c) the length of his legs and the number of steps he took.
2. If distance is measured in kilometres and time in hours, the speed will be in:
a) kiloseconds per metre
b) metres per second
c) kilometres per hour.

11. 9K Quick quiz
3. The best formula for finding the distance when you know the speed and time is:
a) d =
b) d = 2st2
c) d = s × t.
s t
4. A car travels at 55 km/h. How long will it take to get to London, 110 km away?
a) 5 hours
b) 2 hours
c) 30 minutes.

12. 6. How many seconds in one hour ten minutes? a) 3600 b) 70 c) 4200.
9K Quick quiz
5. A woman leaves home on a horse, travelling at 25 km/h. Two hours later her husband leaves in a car, travelling at 75 km/h. They are both going to a farm 75 km away. When will they arrive?
a) both at the same time
b) the woman first
c) the man first.
6. How many seconds in one hour ten minutes?
a) 3600
b) 70 c)

13. 9K Speeding up
Speed and forces

14. …can change the way you move.
9K What’s the connection?
A force...
…can change the way you move.
So a force could:
slow you down
speed you up
change your direction
If no force acts, your speed will not change.
What force speeds you up when you freewheel downhill on a bicycle?

15. gravity (weight) speeds up diver
9K Forcing a change
In each picture, what force is acting? Is it acting to speed up, slow down or change direction?
gravity (weight) speeds up diver
athlete’s pull speeds up hammer and changes its direction
archer’s pull bends bow
drag of parachute (air resistance) slows down car
force from engine speeds up car

16. air resistance and friction on tyres
9K Balanced forces
Unbalanced forces produce a change in speed or direction.
But if the forces are balanced there is no change in speed. A stationary object stays stationary. A moving object continues moving.
Find the hidden balanced forces.
steady speed
steady speed
weight
air resistance and friction on tyres
force from engine
weight
reaction
weight
weight
reaction
reaction
reaction

17. True or False? 2. Forces are measured in neutrons.
9K Is the force with you?
True or False?
2. Forces are measured in neutrons.
6. To work out how long Jill took to get to Leicester, all you need to know is the average speed of her car.
5. A kilogram bag of apples is pulled towards the Earth with a force of roughly 10 N.
1. An object moving at a steady speed has no unbalanced forces acting on it.
4. A spring balance (newton meter) measures an object’s mass.
3. A force can change something’s speed, direction and shape all at the same time.
You can see what 10 N feels like by holding a 1 kg bag of apples (or anything else that weighs 1 kg).
TRUE!
It might help to know where Jill is, so you can find the distance to Leicester!
FALSE!
It measures weight – it would give a different result on the Moon.
FALSE!
Close, but not close enough – forces are measured in newtons.
FALSE!
If something is moving at a steady speed without changing direction, all the forces must be balanced.
TRUE!
Think of Tim Henman serving at 130 mph. The ball speeds up, changes direction and gets squashed!
TRUE!

18. 9K Speeding up
Slow down!

19. 9K Friction
Newton said that an object will carry on moving at a steady speed in the same direction unless an unbalanced force acts.
If that’s true, it will carry on moving forever.
But we know that things slow down and stop. It’s common sense!
????
So was Newton wrong?
No, it’s just that our common sense is confused by an invisible force…
…friction.

20. Friction can be helpful.
9K The ‘invisible brake’
Friction can be helpful.
If there was no friction, your feet would slip.
What else would go wrong without friction?
Friction is a force that acts between two surfaces that are touching. It opposes their movement and acts as an ‘invisible brake’.
friction caused by surfaces rubbing together
lubricants like oil reduce friction
Think of some situations when we want to reduce the effects of friction.

21. Air resistance depends on speed and area, but how?
9K Air resistance
Air resistance depends on speed and area, but how?
Air resistance is caused by air particles bumping into a moving object.
The faster a racing car travels, the greater the number of collisions with air particles.
Does air resistance increase or decrease as the car accelerates?
What if the car was bigger? Would the air resistance increase or decrease? Explain why.

22. The front of a moving object collides with air (or water) particles.
9K Streamlining
The front of a moving object collides with air (or water) particles.
Streamlined objects have a shape that minimises resistance.
Can you think of some more examples?

23. 9K Parachutes
Click to change the skydiver’s position or open his parachute. Look at his speed and the air resistance each time.

24. See if you understand what happens when people jump into the sky.
9K Parachutes: the inside story
See if you understand what happens when people jump into the sky.
1. What force speeds up the skydiver, acting downwards?
2. Does this force change during the jump?
3. What force slows him down, acting upwards?
4. Does this force change during the jump?
5. What factors affect the size of this force?
6. When is it greatest?
7. When is the speed of fall slowest?