OCR Gateway Science P3 revision cards

Speed = distance
time

Units

• metres per second
• kilometres per hour
• miles per hour
• centimetres per second

Speed camera

• 2 photos measure time
• lines on road usd to measure distance travelled
• radar gun
• light beam reflects back to gun

Graphs

X axis = time

Y axis = distance

horizontal line = object stationary
diagonal line = object moving
curved line = speed changing
gradient steeper = moving faster

Use a ruler to help read information off graphs

Acceleration - an increase in the speed of an object

change in speed
time taken

- units m/s2 (metres per second squared)

Deceleration - decrease in the speed of an object

Velocity - speed of a moving object in a known direction (m/s East)

Acceleration / deceleration graphs

Similar to speed graphs. Take care to check gradient of graph and to read the axis

Forcea are pushes or pulls

Forces measured in newtons (N)

Weight (gravity) causes objects to fall and speed up as they fall

Friction causes an object to slow down

Air resistance causes object falling to Earth to slow down

Force = Mass x Acceleration

F

M X A

Accelerate - needs a pull force from the engine

Balanced - constant speed or at rest - forces equal

Unbalanced - accelerate or decelerate - forces unequal

Braking distance - distance to stop brakes applied

Braking distance affected by - tyres, road surface, speed

Thinking distance - distance to react

Thinking distance affected by - distractions, age, drugs (alcohol), tiredness

Stopping distance = thinking + braking

Work is done when a force moves an object.

Work Done (J) = Energy Transferred (J)

The amount of work done depends on size and distance

Work done = Force (N) x Distance (m)

W

F x d

Power ratings are given to cars.

Work - when force moves

Energy - needed to move force

Power = work done
time taken

Unit of power = Watt

Fuel consumption

• amount of fuel used by a car over a set distance
• greater quantity = lower efficiency

Carbon dioxide emissions = greenhouse gases = global warming = ice caps melting = sea levels rising

Kinetic energy

• movement energy
• increases with mass and speed

Fossil fuels -

• pollution
• non-renewable

Biofuels

• from plants
• renewable

Petrol / diesel cars - fossil fuels
diesel engine more efficient

Electric cars - solar powered or battery
- how do you charge battery?

Crumple zones - designed to absorb and spread kinetic energy

Seatbelt - stretches and slows forward motion

Airbags - absorb energy from forward motion

Active safety features

• directly improve safety of vehicle
• ABS, traction control, safety cage

Passive safety features

• help concentration
• electric windows, cruise control, paddle shift controls adjustable seating

Gravity -

• force of attraction to centre of object
• all accelerate at a rate of 10m/s2 no matter what mass

Air resistance - force caused by molecules acting on surface of falling object

Terminal speed - maximum speed

Reducing resistance -

• shape (streamlining / aerodynamic)
• lubricating

Free fall -

• true if no friction
• above Earth's atmosphere, on Moon

The Motion of a Skydiver

• sky diver jumps they accelerate
• gravity acts as a force of attraction
• speed of sky diver increases
• as speed increases so does air resistance
• the maximum speed is called terminal speed
• after the parachute opens unbalanced forces act again
• increased air resistance builds up
• eventually forces balance and sky diver falls at a steady speed

Other things affected by air resistance

• shuttlecocks
• roof boxes
• deflectors
• F1 cars

Gravitational potential -

• energy 'stored' when object high up
• depends on mass and height

Energy transfers -

• gravitational transferred to kinetic
• energy cannot return as some transferred to sound and heat

Conservation of energy = kinetic at bottom + energy transferred due to friction

kinetic energy = 1 mv2
2

• on most theme park rides the cars start high up with lots of gravitational potential energy
• as the cars drop most energy is transferred to kinetic energy
• the car reaches its highest speed at the bottom of a drop
• as the car rises again the kinetic energy is transferred back to gravitational potential energy.
• the second rise will never be as high as the first as some of the initial gravitational potential energy is 'lost' as heat and sound energy

Mass of car doubles = kinetic energy doubled

Speed of car doubles = kinetic energy quadruples

GPE

m x g x h