Each force in an interaction pair acts on a different object. The forces are equal in size and opposite in direction.
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What is the resultant force?
The resultant force on an object is the sum of the individual forces that act on it, taking their directions into account.
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What are reaction of surfaces?
Eg. Vincent's feet push down on floor. Floor pushes up onto his feet with equal force.
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What is Friction?
Eg. Dave tries to push a skip. The force of friction stops the skip from moving.
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What happens if force on friction is increased?
If Dave pushes harder, the size of the friction force increases until reaches limit. Then skip moves.
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How does friction arise?
Initially, there was no friction between the road and the skip. Friction arose in response to the force Dave applied.
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How do objects start moving?
When car starts, the wheels turn. Exerting backward pushing force on the road. Other force in the interaction pair is the same size, the forward force. This makes the car move.
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Objects moving : example
E.g. When you walk, foot pushes back on ground, friction between foot and ground push you forward with equal force.
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How do rockets move?
A rocket pushes out hot gas as fuel burns. Rocket pushes down on these gases. Gas exerts an equal and opposite force on the rocket, pushing it upwards.
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How do jet engines move?
A jet engine draws in air at the front. Then pushes the air out at the back. An equal and opposite force pushes the engine forwards.
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What is a driving force?
E.g. Alex pushes Sam on a skateboard. Alex exerts the driving force pushing it forward.
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What is a counter force?
E.g. The counter force in the opposite direction of Alex and Sam is caused by air resistance and friction.
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What happens if the driving force is greater than the counter force?
The skateboard would speed up.
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What happens if the driving force is equal to the counter force?
The skateboard moves at a constant speed.
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What happens if the driving force is less than the counter force?
The skateboard slows down.
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What is the equation to calculate average speed?
speed (m/s) = distance travelled (m) / time (s)
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What is the instantaneous velocity of an object?
The instantaneous velocity of an object is the instantaneous speed in a certain direction.
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What is acceleration?
The acceleration of a car is the change of speed, or change of velocity in a given time interval.
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What is the equation to calculate acceleration?
acceleration (m/s) = change in velocity (m/s) / time taken (s)
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How can we describe motion?
Distance Time Graphs.
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Distance Time Graphs
The steeper the gradient, the greater the speed.
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What is the displacement of an object?
The displacement of an object at a given time is the straight line distance from its starting point, with an indication of direction.
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What is a speed distance time graph?
Speed distance time graphs show how speed varies with time.
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What is a velocity graph?
Velocity graphs show the velocity of an object at every instance of its journey.
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What is the equation for momentum?
momentum (kg m/s) = mass (kg) x velocity (m/s)
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What is the equation for change in momentum?
change in momentum (kg m/s) = resultant force (N) x time for which it acts (s)
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What are crumple zones?
Crumple zones on cars crush slowly during a collision. This makes the collision last longer and the resultant force on the car is less.
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What are the purpose of seatbelts?
Seatbelts stretch in a collision. This makes the change of momentum longer so the force is less.
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What is the purpose of a helmet?
Helmets change shape when they hit something. Your head stops moving slower, so the force on it is less.
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What is the purpose of airbags?
Airbags increase the time for the change in momentum.
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What is the equation for work done?
work done by a force (J) = force (N) x distance moved by the force (m)
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What is the equation for the amount of energy transferred?
amount of energy transferred (J) = work done (J)
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What is the equation for change in gravitational potential energy?
change in GPE (J) = weight (N) x vertical height difference (m)
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Other cards in this set
Card 2
Front
What is the resultant force?
Back
The resultant force on an object is the sum of the individual forces that act on it, taking their directions into account.
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