Physics P4 (OCR21)
 Created by: Alex
 Created on: 070510 09:40
Fullscreen
SPEED
 Speed = Distance/Time
 EXAMPLE: A cat skulks 20 metres in 40 seconds. Find: a) its speed, b) how long it will take to skulk 75m.
 a) speed = 20/40 = 0.5ms^1
 b) time = 75m/0.5ms^1 = 150s
 Pretty rare in real life for an object to stay at exactly the same speed for a long period of time.
 Usually want to find the average speed if the speed varies constantly for a long period of time.
 Speed cameras take an instantaneous speed of a car: Evenly spaced lines are printed on the road and the speed camera measures the time in which the car travels over the lines.
SPEED AND VELOCITY
 On a distance time graph:

 Gradient = speed
 Flat sections = stationary
 Steep gradient = faster speed
 'Downhill' = travelling in opposite direction
 Curves = Acceleration/deceleration
 Steepening curve = speeding up
 Levelling off curve = slowing down
 Gradient = Δy/Δx
 Always use standard units: m, kg, l etc.
 Distances can be positive or negative.
 0 is always start point, +ve = one direction, ve = other direction.
 Speed is the gradient of a distance/time graph.
 Speed = how fast something is going, it does not have a direction .
 Velociy describes the speed and direction of an object.
 Speed = scalar quantity (mass, temperature, time, length).
 Velocity = vector quantity (force, acceleration, momentum).
VELOCITY
 Velocity can be positive or negative.
 Travel one direction at 20ms^1, turn around and travel in the opposite direction at 20ms^1.
 If two objects heading in opposite directions, one can be said to have positive veolcity while the other have a negative velocity.
 On a velocity/time graph:
 Gradient = acceleration
 Flat sections = steady speed
 Steeper sections = greater acceleration/deceleration
 'Uphill' = acceleration
 'Downhill' = deceleration.
 Area under any section (or all of) graph is equal to the distance travelled in that time interval.
 Curve = changing accelerations
 Tachographs plot speed/time when direction isn't important.
 Tachographs are found in lorries to tell managers how long a driver has gone without a break or if they have been speeding.
FORCES AND FRICTION
 Forces occur when two objects interact
 When an object exerts a force on another subject, it interacts with an opposing force: an 'interaction pair'.
 If you push against a wall, the wall will push back just as hard.
 As soon as you stop pushingthe wall, so does the wall.

If there was no opposing force, you and the wall would fall down.
 If you exert a force of 10N, the wall's results force will be 10N.
 NEWTON'S THIRD LAW!: If object A exerts a force on object B, then object B exerts an equal and opposite force on object A.
 Moving object usually experience friction.
 When an object is moving relative to another, both objects experience a force in the direction that opposes the movement  FRICTION!
 Friction between solid surfaces which are gripping (static).
 The Earth's tectonic plates trying to move but friction is so strong they stay put.
 Friction between solid…
 Friction between solid surfaces which are gripping (static).
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Physics P4 (OCR21)
 Created by: Alex
 Created on: 070510 09:40
Fullscreen
SPEED
 Speed = Distance/Time
 EXAMPLE: A cat skulks 20 metres in 40 seconds. Find: a) its speed, b) how long it will take to skulk 75m.
 a) speed = 20/40 = 0.5ms^1
 b) time = 75m/0.5ms^1 = 150s
 Pretty rare in real life for an object to stay at exactly the same speed for a long period of time.
 Usually want to find the average speed if the speed varies constantly for a long period of time.
 Speed cameras take an instantaneous speed of a car: Evenly spaced lines are printed on the road and the speed camera measures the time in which the car travels over the lines.
SPEED AND VELOCITY
 On a distance time graph:

 Gradient = speed
 Flat sections = stationary
 Steep gradient = faster speed
 'Downhill' = travelling in opposite direction
 Curves = Acceleration/deceleration
 Steepening curve = speeding up
 Levelling off curve = slowing down
 Gradient = Δy/Δx
 Always use standard units: m, kg, l etc.
 Distances can be positive or negative.
 0 is always start point, +ve = one direction, ve = other direction.
 Speed is the gradient of a distance/time graph.
 Speed = how fast something is going, it does not have a direction .
 Velociy describes the speed and direction of an object.
 Speed = scalar quantity (mass, temperature, time, length).
 Velocity = vector quantity (force, acceleration, momentum).
VELOCITY
 Velocity can be positive or negative.
 Travel one direction at 20ms^1, turn around and travel in the opposite direction at 20ms^1.
 If two objects heading in opposite directions, one can be said to have positive veolcity while the other have a negative velocity.
 On a velocity/time graph:
 Gradient = acceleration
 Flat sections = steady speed
 Steeper sections = greater acceleration/deceleration
 'Uphill' = acceleration
 'Downhill' = deceleration.
 Area under any section (or all of) graph is equal to the distance travelled in that time interval.
 Curve = changing accelerations
 Tachographs plot speed/time when direction isn't important.
 Tachographs are found in lorries to tell managers how long a driver has gone without a break or if they have been speeding.
FORCES AND FRICTION
 Forces occur when two objects interact
 When an object exerts a force on another subject, it interacts with an opposing force: an 'interaction pair'.
 If you push against a wall, the wall will push back just as hard.
 As soon as you stop pushingthe wall, so does the wall.

If there was no opposing force, you and the wall would fall down.
 If you exert a force of 10N, the wall's results force will be 10N.
 NEWTON'S THIRD LAW!: If object A exerts a force on object B, then object B exerts an equal and opposite force on object A.
 Moving object usually experience friction.
 When an object is moving relative to another, both objects experience a force in the direction that opposes the movement  FRICTION!
 Friction between solid surfaces which are gripping (static).
 The Earth's tectonic plates trying to move but friction is so strong they stay put.
 Friction between solid…
 Friction between solid surfaces which are gripping (static).
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