Newton's Laws and freefall

Falling bodies

Newton's First Law applies particularly well under freefall conditions.

Sky divers who jump from a plane do not continue to accelerate to the ground at ever increasing speeds – if they did, how could they create spectacular formations?

After jumping out of a plane the skydiver begins to accelerate downwards at 9.8 9\cdot 8 m\,s^{-2}.

However, as the skydiver's speed increases the frictional force due to air resistance also increases.

There comes a point when the skydiver's upward frictional force equals the skydiver's downward weight.

The forces are now balanced.

If the vertical forces on the skydiver are balanced then according to Newton's First Law, the skydiver will continue downwards at a constant speed.

This constant speed (or velocity) is known as the terminal velocity

The bird in the picture below has the same issue.

A bird diving towards its prey with an arrow pointing up labelled 'F (friction)' and a label pointing down labelled 'W (weight)'.

The bird will fall on its prey with a constant velocity due to balanced forces.