Newton I and III

After studying this section you should be able to:

  • identify the forces acting on an object that is not changing its velocity
  • for a given force, describe the other force that makes up the third law ‘pair’

Newton’s laws of motion
With his three laws of motion, Newton thought that he could describe and predict the movement of every object in the Universe. Like many other ‘laws’ in physics, they give the right answers much of the time. The paths of planets, moons and satellites are all worked out using Newton’s laws.

The ideas behind the three laws have already been used informally in this chapter. This section looks at formal statements of the first and third laws and how they apply to everyday situations.