# Physics P2 - Edexcel

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• Created by: Mia
• Created on: 29-05-12 20:58

Physics P2

Velocity

Speed – how fast you’re going

Velocity – how fast you’re going in what direction.

Distance in a particular direction is called displacement.

Average velocity = displacement / time

Speed cameras use the lines painted on the ground to see how fast a car is going in a certain number of seconds.

Acceleration = change in velocity / time taken

Forces

• Stationary object – all forces in balance

• Steady velocity – all forces in balance

• Acceleration – unbalanced forces

Balanced force – steady speed and direction

Resultant force – acceleration

Resultant force = mass x acceleration

Reaction forces – if an object exerts a force on another object, that object will exert the exact opposite force

Friction and Drag

Always there, slows things down, always in the opposite direction to movement.

Steady speed = driving force needs to balance the friction

Reduce drag – use streamlining

Drag increases as speed increases

Terminal velocity

When resistance force = accelerating force – cannot go any faster

Stopping distance

Thinking distance – speed and attention

Breaking distance – speed, weight, brakes and grip

Car safety

Momentum = Mass x velocity

The longer the change in momentum the smaller the force once it reaches impact, so cars have:

1) Crumple zones – increase the time taken for the car to stop.

2) Seat belts – stretch slightly increasing the time taken for the wearer to stop, reduces forces acting on the chest.

3) Air bags – slightly increasing the time taken for the driver to reach impact.

Kinetic Energy

Kinetic energy = ½ x Mass x Velocity2

Work done

Work done = Force x Distance

Electrical energy

Electrical energy = voltage x current x time

Gravitational Potential energy

Potential energy = mass x g (normally 10) x height

Conservation of energy

Energy is never created or destroyed – only converted from one form to another.

Energy is only useful when it’s converted from one form to another.

Kinetic energy gained = potential energy lost

Speed of falling object = potential energy is converted into kinetic energy.

Power – watts or J/s

Power = work done / time taken

Power Output

Power output = energy transferred (potential or kinetic energy) / time taken

Circular motion

Velocity is both the speed and direction of an object so when going in a circle the velocity is always changing so this means there must be a force acting on it = centripetal force.

Centripetal Force (N) = (Mass x Speed2) / Radius

Einstein’s relativity

Used thought experiments – fancy way of…