P3: Forces for Transport OCR Gateway Additional Science 16/10/2017 P3: Forces for Transport OCR Gateway Additional Science W Richards

16/10/2017 P3a Speed

Distance, Speed and Time 16/10/2017 16/10/2017 16/10/2017 Distance, Speed and Time D T S Speed = distance (in metres) time (in seconds) Freddie walks 200 metres in 40 seconds. What is his speed? Hayley covers 2km in 1,000 seconds. What is her speed? How long would it take Lauren to run 100 metres if she runs at 10m/s? Jake travels at 50m/s for 20s. How far does he go? 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

Distance, Speed and Time 16/10/2017 16/10/2017 16/10/2017 Distance, Speed and Time D T S Speed = distance (in metres) time (in seconds) Sarah walks 2000m in 50 minutes. What is her speed in m/s? Jack tries to walk the same distance at a speed of 5m/s. How long does he take? James drives at 60mph (about 100km/h) for 3 hours. How far has he gone? 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

How speed cameras work 16/10/2017 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? After 1.5s After 0s

Average Speed 16/10/2017 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. s = u + v 2 t Two cameras are 1km apart and a car takes 50s to travel between them. What was the car’s average speed? A car accelerates from 10 to 20m/s for 50s. How far has it gone? 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

Distance-time graphs 2) Horizontal line = 40 30 20 10 16/10/2017 2) Horizontal line = 40 30 20 10 4) Diagonal line downwards = Distance (metres) 3) Steeper diagonal line = Time/s Diagonal line = 20 40 60 80 100

What is the speed during the first 20 seconds? 40 30 20 10 16/10/2017 Distance (metres) Time/s 20 40 60 80 100 What is the speed during the first 20 seconds? How far is the object from the start after 60 seconds? What is the speed during the last 40 seconds? When was the object travelling the fastest?

Distance-time graph for non-uniform motion 16/10/2017 Object is accelerating up to here 40 30 20 10 Object is now decelerating Distance (metres) Time/s 20 40 60 80 100

40 30 20 10 20 40 60 80 100 1.5m/s 0.5m/s 1m/s Distance (metres) 16/10/2017 16/10/2017 16/10/2017 Distance (metres) Time/s 20 40 60 80 100 What was the velocity in the first 20 seconds? What was the velocity between 20 and 40 seconds? When was this person travelling the fastest? What was the average speed for the first 40 seconds? 1.5m/s 0.5m/s 80-100s 1m/s

16/10/2017 P3b Changing Speed

Acceleration V-U T A Acceleration = change in velocity (in m/s) 16/10/2017 16/10/2017 16/10/2017 V-U T A Acceleration Acceleration = change in velocity (in m/s) (in m/s2) time taken (in s) A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration? A ball is dropped and accelerates downwards at a rate of 10m/s2 for 12 seconds. How much will the ball’s velocity increase by? A car accelerates from 10 to 20m/s with an acceleration of 2m/s2. How long did this take? 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

Speed-time graphs 1) Upwards line = 80 60 40 20 4) Downward line = 16/10/2017 1) Upwards line = 80 60 40 20 4) Downward line = Velocity m/s 3) Upwards line = 2) Horizontal line = T/s 10 20 30 40 50

How fast was the object going after 10 seconds? 80 60 40 20 16/10/2017 16/10/2017 16/10/2017 Velocity m/s T/s 10 20 30 40 50 How fast was the object going after 10 seconds? What is the acceleration from 20 to 30 seconds? What was the deceleration from 30 to 50s? How far did the object travel altogether? 40m/s 2m/s2 3m/s2 1700m

Speed-time graph for non-uniform motion 16/10/2017 Object’s acceleration is increasing 40 30 20 10 Object’s acceleration is decreasing Distance (metres) Time/s 20 40 60 80 100

How fast was the object going after 10 seconds? 80 60 40 20 16/10/2017 16/10/2017 16/10/2017 Velocity m/s T/s 10 20 30 40 50 How fast was the object going after 10 seconds? What is the acceleration from 20 to 30 seconds? What was the deceleration from 40 to 50s? How far did the object travel altogether? 10m/s 4m/s2 6m/s2 1500m

80 60 40 20 16/10/2017 16/10/2017 16/10/2017 Velocity m/s T/s 10 20 30 40 50 This velocity-time graph shows Coryn’s journey to school. How far away does she live? 2500m

Speed vs. Velocity Speed is simply how fast you are travelling… 16/10/2017 16/10/2017 16/10/2017 Speed is simply how fast you are travelling… This car is travelling at a speed of 20m/s Velocity is “speed in a given direction”… This car is travelling at a velocity of 20m/s east

Circular Motion 1) Is this car travelling at constant speed? 16/10/2017 16/10/2017 16/10/2017 1) Is this car travelling at constant speed? 2) Is this car travelling at constant velocity?

16/10/2017 P3c Forces and Motion

Force and acceleration 16/10/2017 16/10/2017 16/10/2017 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) F A M

Force, mass and acceleration 16/10/2017 16/10/2017 16/10/2017 A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate? A force of 3000N acts on a car to make it accelerate by 1.5m/s2. How heavy is the car? A car accelerates at a rate of 5m/s2. If it weighs 500kg how much driving force is the engine applying? A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by? F A M 2m/s2 2000kg 2500N 0.5m/s2

Stopping a car… 16/10/2017 16/10/2017 16/10/2017 What two things must the driver of the car do in order to stop in time?

Total Stopping Distance = Thinking Distance + Braking Distance Stopping a car… 16/10/2017 16/10/2017 16/10/2017 Tiredness Too much alcohol Thinking distance (reaction time) Too many drugs Poor visibility Wet roads Icy roads Braking distance Tyres/brakes worn out Driving too fast Total Stopping Distance = Thinking Distance + Braking Distance

Stopping Distances Thinking distance increases linearly 16/10/2017 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

16/10/2017 P3d Work and Power

Weight vs. Mass 16/10/2017 16/10/2017 16/10/2017 Earth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N. W g M Weight = Mass x Gravitational Field Strength (in N) (in kg) (in N/kg) What is the weight on Earth of a book with mass 2kg? What is the weight on Earth of an apple with mass 100g? James weighs 700N on the Earth. What is his mass? On the moon the gravitational field strength is 1.6N/kg. What will James weigh if he stands on the moon? 20N 1N 70kg 112N

Work done = Force x distance moved 16/10/2017 16/10/2017 16/10/2017 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 W D F

Example questions 25J 20J, GPE 4m, KE 50N 2MJ 16/10/2017 16/10/2017 16/10/2017 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? 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? 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? Jack cuddles his cat and lifts it 1.5m in the air. If he did 75J of work how much force did he use? 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

A Practical Example of Doing Work 16/10/2017 16/10/2017 Consider a rocket re-entering the Earth’s 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

In other words, 1 Watt = 1 Joule per second Energy and Power 16/10/2017 16/10/2017 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 T P E = Energy (in joules) P = Power (in watts) T = Time (in seconds)

Some example questions 16/10/2017 16/10/2017 What is the power rating of a light bulb that transfers 120 joules of energy in 2 seconds? What is the power of an electric fire that transfers 10,000J of energy in 5 seconds? Tanner runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating? How much energy does a 150W light bulb transfer in a) one second, b) one minute? Pierre’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a 50 minute physics lesson? Levi’s 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

What are the advantages and disadvantages of each car? An example with cars 16/10/2017 Citroen Saxo, 60bhp Audi R8, 423 bhp What are the advantages and disadvantages of each car?

Power W P = W t t W = FxD P = W = FxD t t P = Fv 16/10/2017 16/10/2017 Power (in watts) is “the rate of doing work”: W t P P = W t Also, using our “work done” equation: W = FxD P = W = FxD t t …therefore P = Fv

Random questions on work and power 16/10/2017 16/10/2017 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 Jordan’s power rating. 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. 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 50N

16/10/2017 P3e Energy on the Move

Kinetic energy = ½ x mass x velocity squared 16/10/2017 16/10/2017 16/10/2017 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

Example questions 16/10/2017 16/10/2017 16/10/2017 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? 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? Will is running and has a kinetic energy of 750J. If his mass is 60kg how fast is he running? Josh is walking to town. If he has a kinetic energy of 150J and he’s walking at a pace of 2m/s what is his mass? 450,000J 4000J 5m/s 75kg

Stopping Distances revision 16/10/2017 Recall the patterns we observed in this data: Thinking distance increases linearly Braking distance increases in a squared relationship

What happens inside the car when it stops? Stopping a car… 16/10/2017 16/10/2017 16/10/2017 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

An example question… 16/10/2017 16/10/2017 16/10/2017 This car can apply a maximum braking force of 10,000N. If the car’s 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)

Different ways of fuelling cars 16/10/2017 What are the advantages and disadvantages of each of the following fuels?

Fuel consumption 16/10/2017 How do the following features help or hinder fuel economy? Having an aerodynamic shape Having a roof box Having a “deflector” Having a window open

16/10/2017 P3f Crumple Zones

Momentum 16/10/2017 16/10/2017 16/10/2017 Any object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula: P V M Momentum = Mass x Velocity (in kgm/s) (in kg) (in m/s) 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

Force and momentum mv T F 16/10/2017 Newton’s second law of motion says that the force acting on an object is that object’s rate of change of momentum. In other words… mv T F Force = Change in momentum Time (in N) (in kgm/s) (in s) Also called “impulse” 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

Example questions 16/10/2017 16/10/2017 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. Courtney thinks it’s 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 ball’s change in momentum and its speed. 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. 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

Safety features mv T F Basically: 16/10/2017 16/10/2017 16/10/2017 How do air bags and crumple zones work? mv T F 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

Car Safety Features 16/10/2017 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.

16/10/2017 P3g Falling Safely

Introduction to Forces 16/10/2017 16/10/2017 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

Examples of Air Resistance 16/10/2017 Examples of Air Resistance

Balanced and unbalanced forces 16/10/2017 16/10/2017 16/10/2017 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 doesn’t move anywhere. Weight

Balanced and unbalanced forces 16/10/2017 16/10/2017 16/10/2017 Reaction What would happen if we took the road away? Weight

Balanced and unbalanced forces 16/10/2017 16/10/2017 16/10/2017

Balanced and unbalanced forces 16/10/2017 16/10/2017 16/10/2017 1) This animal is either ________ or moving with _______ _____… 2) This animal is getting ________… 3) This animal is getting _______…. 4) This animal is also either _______ or moving with ________ ______.. Words - Stationary, faster, slower or constant speed?

Summary Complete these sentences… 16/10/2017 16/10/2017 16/10/2017 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… …accelerate in the direction of the resultant force …continue to move at the same speed and the same direction …continue to stay stationary …accelerate in the direction of the resultant force

Words – increase, small, constant, balance, accelerates Terminal Speed 16/10/2017 Consider a skydiver: 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 skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL SPEED Words – increase, small, constant, balance, accelerates

Words – slowing down, decrease, increases, terminal speed, weight 16/10/2017 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

Velocity-time graph for terminal velocity… 16/10/2017 Parachute opens – diver slows down Velocity Speed increases… Terminal velocity reached… On the Moon Diver hits the ground New, lower terminal velocity reached Time

Acceleration due to Gravity 16/10/2017 Notice that the skydiver’s weight didn’t 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

P3h The Energy of Games and Theme rides 16/10/2017 P3h The Energy of Games and Theme rides

Gravitational Potential Energy 16/10/2017 16/10/2017 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) GPE H mg (Remember - W=mg)

Some example questions… 16/10/2017 16/10/2017 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

Energy changes for a skydiver 16/10/2017 Recall our skydiver: If the skydiver has reached terminal speed explain what happens to his… Kinetic energy Gravitational potential energy …while he is falling.

Understanding Kinetic Energy 16/10/2017 KE = ½ mv2 If the mass of the object is doubled what effect would this have on the object’s kinetic energy? If the speed of the object is doubled what effect would this have on the object’s kinetic energy?

Roller Coasters 16/10/2017 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

Using conservation of energy when dropping objects 16/10/2017 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 1m h = v2 2g v2 = 2 x 10 x 1 v2 = 20 v = 4.5m/s

An example question… 16/10/2017 16/10/2017 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?