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Forces and Motion

Calculation for the Velocity of a Falling Object.
See the previous page for the forces on a falling Object.

Q1. An object falls from a cliff.
How fast will it be moving after 3 seconds?

A.  Use   a = (v-u) ÷ t

a = 10 m/s2 because of gravity.
  u = 0 (initial downward velocity).
t = 3

If you are good at maths,
you can rearrange the equation to give v - u = a x t.

v - 0 = 10 x 3
v = 30 m/s.
In reality, the velocity will be a little less than this because
air resistance (friction) will slow the falling object down.

You may have noticed that the above calculation
takes no account of the mass or weight of the falling object.
All things fall with the same acceleration, so if both a
penny and a car were thrown from a cliff at the same time,
they would both hit the ground at the same time.

Things will fall noticeably slower if
1. their density is close to the density of air
(for example a feather)
or
2. they have a large air resistance in proportion to their weight
(for example a parachute).

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