# P4 - Physics GCSE

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What is velocity?
A measurement of an object's speed and direction of travel.
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What is the formula for speed?
Speed (m/s) = Distance travelled (m) / Time taken (s). This calculates average speed.
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What is instantaneous speed?
The speed of an object at a particular point in time.
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What is a distance-time graph?
A plot of distance against time, the gradient of which is a measure of the object's speed- the steeper the slope, the greater the speed.
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What is displacement?
A measurement of distance from a fixed point or origin. It can take a positive or negative value, depending on the direction from the origin.
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What is a displacement-time graph?
A plot of displacement against time, the gradient of which gives the object's velocity, so it can have a positive or negative gradient.
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What is instantaneous velocity?
The speed and direction of an object at any given time.
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What does a curved distance-time graph show?
The speed of the object is changing as it travels. Plotting a straight line from beginning to end can give the average speed, but it is difficult to calculate instantaneous speed from it.
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What is a speed-time graph?
A plot of speed against time, the gradient of which gives the object's acceleration. The steeper the slope, the faster the rate of acceleration.
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What is a velocity-time graph?
A plot of velocity against time, the gradient of which gives the object's acceleration. Because velocity is involved, one axis can have negative values.
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What is the formula for acceleration?
Acceleration (m/s (squared)) = Change in speed (m/s) / Time taken (s).
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What is an interaction pair?
Two equal and opposite forces that occur when two objects interact with each other and one exerts a force on the other.
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What is gravity?
The force of attraction between two masses, e.g. people to the Earth.
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What is air resistance?
The force of the air pushing against an object, slowing it down.
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What happens in rocket and jet engines?
The engine pushes has backwards (action) and the gas pushes the rocket forward (reaction).
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What is the reaction of the surface?
A force that occurs as a result of an object resting on a surface, being pulled down by gravity. The force is of the surface pushing up on the object.
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What is friction?
The force that occurs when two objects slide past each other, in order to stop the objects moving.
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How are forces shown on a diagram?
Arrows represent forces: the size of the arrow shows the size of the force, and the direction of the arrow shows the direction the force is moving in.
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What is a resultant force?
The overall effect of adding or subtracting the forces working on an object (forces in the same direction are added, those in an opposite direction are taken away).
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What is momentum?
The measure of the motion of an object.
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What is the formula for momentum?
Momentum (kg m/s) = Mass (kg) X Velocity (m/s).
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What happens when the resultant force acting on an object is zero?
The object's momentum will not change (if it is stationary, it will remain stationary; if it is already moving, it will continue moving at a steady speed in the same direction).
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What happens if the resultant force acting on an object is not zero?
A change in momentum occurs- the object could speed up, slow down, start moving, or change direction.
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What is the formula for change in momentum?
Change in momentum (kg m/s) = Resultant force (newtons, N) X Time the force acts for (s).
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What is a collision?
Where two objects come together, causing changes in the momentum. In a car crash, the sudden changes in momentum can affect the car and the passengers, leading to damages and injuries.
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Seat belts, air bags, crumple zones (at the front, which crumple on impact) etc. which reduce the impact of the collision on the passengers.
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What is a vehicle's driving force?
The forward force created by the engine or other energy source (cyclists etc.).
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What is a counter force?
The force on an object, caused by friction and air resistance.
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Why does a vehicle speed up?
The driving force is bigger than the counter force.
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Why does a vehicle travel at a constant speed?
If the driving force is equal to the counter force.
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Why does a vehicle slow down?
The driving force is smaller than the counter force.
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What is kinetic energy?
The energy of a moving object, dependent on its mass and velocity.
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What is the formula for kinetic energy?
Kinetic energy = 1⁄2 × mass × speed(squared)
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What forces act on an object thrown upwards?
Air resistance and gravity- they slow down the object, which is moving as a result of the initial force upwards.
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What forces act on a falling object?
Gravity- pulls the object downwards, causing it to accelerate and the air resistance force to increase. When air resistance and gravity are equal, the object moves at a constant speed.
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What is work done?
A transfer of energy, as a result of a force acting on an object. If the work is done on an object, it gains energy; if the work is done by an object, it loses energy. The total amount of energy remains the same (it is conserved).
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What happens when a force makes an object's velocity increase?
Work is done on the object by the force, and the object gains kinetic energy.
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What is the formula for work done?
Work done (J) = Force (N) X Distance moved in the force's direction (m).
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What is GPE?
Gravitational Potential Energy- the energy created by the work done on an object being lifted. It has the potential to do work.
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What is the formula for GPE?
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 formula for speed?

#### Back

Speed (m/s) = Distance travelled (m) / Time taken (s). This calculates average speed.

### Card 3

#### Front

What is instantaneous speed?

### Card 4

#### Front

What is a distance-time graph?

### Card 5

#### Front

What is displacement?