# Physics definitions G484

A set of all the definitions you need to know for ocr A physics unit G484

- Created by: grace
- Created on: 27-09-10 09:31

## NEWTONS FIRST LAW

A force is neccessary to change the state of rest, or of uniform motion in a straight line of a body.

- If you are staionary you will remain stationary unless a resultant force acts upon you.
- If you want to change your direction of travel a resultant force must act upon you.
- If you want to speed up or slow down a resultant force must act upon you.
- If you are moving with constant velocity there is zero resultant force acting upon you.

## NEWTONS SECOND LAW

The rate of change of momentum of an object is directly proportional to the resultant (net) for acting upon it.

## THE NEWTON

One newton is the force that will give a mass of one kilogram an accelleration of one metre per second

## LINEAR MOMENTUM

The mass of an object multiplied by its velocity

change in momentum = force x time

## NEWTONS THIRD LAW

When body A exerts a force on body B, body B exerts a force that is

- equal
- opposite in direction
- the same type

## CONSERVATION OF MOMENTUM

In any direction, in the absence of external forces the total momentum of a system remains constant.

## IMPULSE

Impulse = Change in momentum of a body

equal to area underneath a force - time graph

## ELASTIC COLLISIONS

In a perfectly elastic collison NO momentum or kinetic energy is lost

## INELASTIC COLLISIONS

In an elastic collision momentum is conserved but kinetic energy is not.

## RADIANS

One radian is the angle subtended at the centre of a circle by an arc of lenth equal to the circles radius.

## THE PERIOD

The period of an object in circular motion is the time taken for it to complete one revolution.

In equation form it it is

period = circumference/velocity

## CENTRIPETAL ACCELERATION

The centripetal acceleration of an object travelling in a circle of radius r with constant velocity is given by the equation:

acceleration = velocity squared / radius

in a direction towards the centre of the circle

## A FIELD

The region in which a force operates

## GRAVITATIONAL FIELD STRENGTH

The gravitational field strength at any point is the force acting per unit mass at that point

## GRAVITATIONAL FORCE

The gravitational force of attraction between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

## KEPLARS THIRD LAW

The period of a planet squared equals the mean radius of its orbit

## TERMS TO DESCRIBE OSCILLATIONS

DISPLACEMENT - The distance an object has moved form its mean / rest position.

AMPLITUDE - Maximum displacement

FREQUENCY- The number of oscillations per unit time at any point

PERIOD (OF OSCILLATION) - Time for one complete pattern of oscillation to take place at any point

## SIMPLE HARMONIC MOTION

An object undergoing simple harmonic motion:

- Has an acceleration proportional to its displacement from a fixed point

- Accelerates in the opposite direction to the displacement

## DAMPING

Deliberately reducing the amplitude of an oscillation

## RESONANCE

The build-up fo an large amplitude oscillation when the frequency of vibrating objects match

## DENSITY

Mass per unit volume

## PHASE

Whether a substance is in the form of solid, liquid or gas

## PRESSURE

Force per unit area

## INTERNAL ENERGY

The internal energy of a body is the sum of the random distributions within it and also all the potential energies of molecules in its body.

## IDEAL GAS

A gas that has internal energy only in the form of random kinetic energy.

## THERMAL EQUILIBRIUM

Two objects at the same temperature

## SPECIFIC HEAT CAPACITY

The quantity of thermal energy required to raise the temperature of a unit mass of a substance by a unit temperature rise.

## SPECIFIC LATENT HEAT OF FUSION

The quantity of energy per unit mass required to change it at constant temperature from a solid to a liquid.

## SPECIFIC LATENT HEAT OF VAPOURISATION

The specific latent heat of vapourisation od a substance is the quantity of energy per unit mass required to change it at constant temperature from liquid to vapour.

## BOYLES LAW

The volume of a fixed mass of gas is inversely proportional to the pressure exerted on it, provided that temperature is constant.

## IDEAL GAS EQUATION

for a fixed mass of an ideal gas, at constant temperature, its volume V is proportional to the ideal gas temperature T.

T will be in kelvin.

## THE MOLE

This can be used to determine the number of molecules in any quantity of any substance.

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