ocr gateway science p3 revision cards
TRANSCRIPT
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Speed 2
Graphs
X axis = time
Y axis = distance
horizontal line = object stationary diagonal line = object moving curved line = speed changinggradient steeper = moving faster
Use a ruler to help read information off graphs
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Speed
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
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Forces and Motion
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
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Changing Speed
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
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Work and Power
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.
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Forces and Motion
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
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Energy on the Move
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?
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Work and Power
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 levelsrising
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Falling Safely
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
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Crumple Zones
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
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The Energy of Theme Park Rides
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
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Falling Safely
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
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The Energy of Games and Theme Park Rides
•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