Physics Definitions - Mechanics

Scalar Quantity

has magnitude only (distance, speed, time, mass)

Vector Quantity

has magnitude and direction (displacement, velocity, acceleration, force, momentum)

Speed

rate of change with respect to time

Displacement

distance in a given direction

Velocity

rate of change of displacement with respect to time

Constant Velocity

if an object is moving in a straight line and doesn’t speed up or slow down

Acceleration

rate of change of velocity with respect to time

Force

anything that causes the velocity of an object to change (acceleration), only an outside force can cause the velocity of an object to change, acceleration of a body is directly proportional to the force causing it

Mass

measure of the amount of matter in it

Newton

F=(ma), 1 newton is the force that gives 1kg an acceleration of 1ms-2

Weight

mass x gravity

Momentum

mass x velocity

Principle of Conservation of Momentum

total momentum before the collision is equal to the total momentum after the collision, as long as no external force acts upon it

Newton’s First Law of Motion

every body will remain in a state of rest or travelling at a constant velocity unless an external force acts on it

Newton’s Second Law of Motion

when an unbalanced force acts on a body - the rate of change of the body’s momentum is directly proportional to the force and takes place in the direction of the force

F \~ mv-mu/t

Newton’s Third Law of Motion

for every action and reaction are equal and opposite

Friction

a force that opposes one surface sliding along another

Work

force x distance moved

Joule

1 joule of work is done when a force of 1 Newton moves the point of application 1 metre

Conservation of Energy

total energy is a constant, energy is converted from one form to another

Kinetic Energy

energy a moving body has, Ek = 1/2 mv2

Potential Energy

Energy a body has due to its position, Ep = mgh

Newton’s Universal Law of Gravitation

Any two bodies in the universe attract to each other with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them

F = Gm1m2/r2