Dynamics

Dynamics is the study of forces on an object.

The whole of the topic can be summarised into Newton's 3 laws.

1) An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

2) Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
This law is most famously represented by F=ma

3) For every action there is an equal and opposite re-action.

These can be used to solve many problems.

For example: a 2kg block requires 10N of force to move it at steady speed. What is its acceleration when 20N of force is applied on it?

F =ma, so the resultant force is 10N, since 10N of force is just requied to move it, and
20N - 10N = 10N.
Thus when we plug the numbers into the equation F = ma, we get: 10N = (2kg)(a)

thus the acceleration of the block when 20N of force is applied on it is 5 m/s^2.