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

9K Speeding up How fast?

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

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!)

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

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?

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?

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

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?

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.

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.

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) 4200.

9K Speeding up Speed and forces

…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?

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

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

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!

9K Speeding up Slow down!

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.

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.

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.

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?

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

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?