In everyday life, the terms mass and weight are interchangeable. However, in physics mass and weight do not mean the same.

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The acceleration of a falling object can be calculated using **Newton’s Second Law**, F = ma

If a skydiver has a mass of 60 kg. Her weight is found using:

W = mg

W = 60 kg x 10 N/kg

W = 600 N

If air resistance is ignored, the pull of gravity, 600 N, is the only force acting on the skydiver. Her acceleration is found using:

a =

F = 600 N

m = 60 kg

a =

a = 10 m/s^{2}.

- In the absence of air resistance all objects fall at the same rate regardless of their mass. Near the Earth the rate is the acceleration of free fall, 10 m/s
^{2}. - Due to the Earth’s gravity, the speed of an object dropped from a height will increase at a rate of 10 m/s every second as it falls.
- If there was no air resistance or drag, a feather and a hammer would fall at the same rate of 10 m/s
^{2}. Dropped from the same height, they would both hit the ground at the same time and travelling at the same speed.