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29 Cards in this Set

  • Front
  • Back
Resultant force
The resultant force on an object is the sun of the individual forces that act on it, taking their directions into account. The resultant us the difference and is in the direction of the biggest force.
Reaction force (of surfaces)
A foot pushes dien in the floor. The floor pushes up on his feet with an equal force. The force is the reaction of the surface.
Friction
A force between two objects that opposes the sliding of one object past another. It provides grip also opposing movement. To move something the force exerted on it has to be bigger than the maximum possible friction force.
Counter force
A resistive force that opposes the motion of a moving object.
Interaction pairs
Interaction patner forces are a pair of forces of the same type and size but working in opposite directions.
Weight
The force acting on an object from the gravitational pull over the earth
How do objects start moving
Friction and jet engines and rockets.
A rocket pushes hot gases as is fuel burns, forcing the rocket upwards.
A jet engine draws in air at the front and pushes it out at the back.
How do objects keep moving?
Driving and counter forces. If the driving force is greater than the counter force it speeds up, if equal moves at constant speed. If driving force smaller than counter force it slows down.
Average speed calculation
Speed (m/s) = distance traveled (m) ÷ time (s)
Instantaneous speed
The speed of an object at a particular instance. In practise an average speed over a very short time interval.
Acceleration meaning
Change of speed or change in velocity in a given time interval.
Acceleration calculation
Acceleration (m/s) = change in velocity (m/s) ÷ time taken (s)
Distance time graph
The steeper the gradient the faster the speed. Time against the distance traveled.
Displacement time graph
The displacement of an object at a given time from the starting point, with indication of direction.
Speed time graph
How the speed varies with time.
Velocity time graphs
The velocity of an object at every instant of its journey
Momentum calculation
Momentum (kg m/s) = mass (kg) x velocity (m/s)
Change if momentum calculation
Change of momentum (kg m/s) = resultant force (N) x time for which it acts (s)
Road saftey
If two cars collide and stop their momentum changes until it becomes zero. The more time the change of momentum takes, the smaller resultant force on the car. So less chance of injury than if it was instant.
Road saftey measures
Car crumple zones
Seat belt
Helmets
Air bags
Car crumple zone
Car crumple zones slows the collision, making it last longer minimising resultant force
Seat belt
Seat belts stretch in collision, making the change of momentum last longer. So force is less
Helmets
Helmets change shape when they hit something. Your head stops moving more slowly, so the force is less.
Air bags
Air bags increase the time for change of momentum.
Work done by force calculation
Work done by force (J) =force (N) x distance moved by force (m)
What is equal to work done
Amount of energy transfered (J) = work done (J)
Change in gravitational potential energy calculation
Change in GPS (J) =weight (N) x vertical height difference (m)
What is equal to gravitational potential energy lost
GPE lost = kinetic energy gained
Kinetic energy calculation
KE = 1/2 x mass x (velocity)^2 (squared)