Chapter: 3.4

Newton's first law

Newton’s first law or law of inertia.

The Newton's first law

The first Newton’s law says: When the sum of all external forces applied on the observed object is zero, an object is standing still or moving uniformly. The external forces on the object are in balance.


Let’s take a look on the forces applied on a vase.

The figure shows the vase on which the gravitational force and the force of a table are applied. Since the magnitude of the forces is equal, but their direction is opposite, the vase is standing still.

Test yourself

Observe the figure. Eva and Nick are pulling the rope. 

Which vector represents Eva’s force, if the rope is still?

Petra is holding a toy, like the one in the picture.

What force must she pull to make the strings vertical?

b) The force of one hand must be equal to half the weight of the toy.