# physics unit 2

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• Created on: 03-04-13 22:03

Physics Unit 2 Formulae, Definitions & Notes

The slope on a distance-time graph represents speed

Speed (m/s) = distance travelled (metre, m) / time taken (seconds, s)

Velocity is speed in a given direction

Acceleration (metre/second squared, m/s2) = change in velocity (metre/second, m/s)

time taken for the change (second, s)

The slope on a velocity-time graph represents acceleration. The area under the line on a velocity-time graph represents distance travelled. In order to find the area of a period of constant acceleration represented by a rectangle on the graph, multiply the height by the base.

In order to find the area for a period of acceleration or deceleration, i.e, a triangle; multiply ½ the height by the base.

On a distance-time graph the slope of the line = the height of the triangle

the base of the triangle

When two objects interact, they always exert equal and opposite forces on each other.

The unit of force is the Newton, N. 1N = about 100g on Earth

Resultant force (Newtons, N) = mass (kg) x acceleration (metres/second2)

Thinking distance – distance travelled by the vehicle in the time it takes the driver to react

Braking distance – the distance the vehicle travels under the braking force

Stopping distance = thinking distance + braking distance

Weight of an object – the force of gravity on the object

Mass of an object – the quantity of matter in it

Gravitational field strength = N/kg. GFS at the surface of the Earth is about 10N/kg

Weight = mass (kg) x gravitational field strength (N/kg)

Terminal velocity – when an object reaches a constant velocity where the drag force on it is equal and opposite to its weight. The resultant force is zero, so acceleration is also zero. An object falling freely accelerates at about 10 m/s

Work done (joules, J) = force (N) x distance moved in the direction of the force (m)

The kinetic energy of a moving object depends on its mass and its speed.

Kinetic energy (J) = ½ x mass (kg) x speed2 (m/s2)

Momentum (kg m/s) = mass (kg) x velocity (m/s)

Momentum is conserved in any collision or explosion provided no external forces act on the objects that collide or explode. Momentum has size and direction, and when two objects push each other apart they move apart with equal and opposite momentum.

The more time an impact takes, the less force exerted.

Force (N) = change of momentum (kg m/s)

time taken (s)

To eliminate static electricity use antistatic materials and earth metal pipes and objects.

A battery consists of two or more cells connected together.

The unit of resistance is the Ohm Ω

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