Physics definitions G484

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.

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

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

The mass of an object multiplied by its velocity

change in momentum = force x time

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

• equal
• opposite in direction
• the same type

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

Impulse = Change in momentum of a body

equal to area underneath a force - time graph

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

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

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

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

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

The region in which a force operates

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

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.

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

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

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

Deliberately reducing the amplitude of an oscillation

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

Mass per unit volume

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

Force per unit area

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.

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

Two objects at the same temperature

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

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

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.

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

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.

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