They describe the motion of objects in terms of

their MASS and

the FORCES acting on them

Mass – the amount of matter that an object contains

a measure of the INERTIA of an object or its resistance to a change in motion.

[metric unit of mass is gram, kilogram, centigram...] 1

Force –a PUSH or a PULL– is always acting on an object even if the object is at rest or moving.

[metric unit of force is Newton]

It can cause an object to start moving, stop moving or change direction.

2

Balanced Force

Equal forces in opposite directions produce no change in motion

Unbalanced Forces

Unequal opposing forces produce an unbalanced forcecausing a change in motion

• To move an object at rest or change the motion of a moving object [i.e. accelerate], the forces acting on it must be

• The object will then accelerate in the direction of the greater force

UNBALANCED

Net force is 0, so no motion

Net force to the right+

=

+ =Net force to the right

5

The forces are BALANCED

6

Fg and the push from the table balance each other.

However, there is no force present to balance the force of friction.

As the book moves to the right, friction acts to the left to slow the book down.

This is an unbalanced force. 7

Equilibrium is a state of no change

Equilibrium is a state of no change