Acceleration, Weight and Mass

Weight• Near the surface of the Earth, the pull of

gravity on a body is practically constant and every falling body acquires constant acceleration equal to “g”

• The force that accelerates the body downward is equal to its weight “w”

• It follows that if “m” is the mass of the body, then Newton’s 2nd law equation, F = ma can be restated as:

• This enables us to compute the weight of a body from its mass, or the mass of the body from its weight.

• “g” can also be calculated for another planet by the equation:

Gravitational v. Inertial Mass

• Obtaining a mass measurement based on the pull of gravity on a body is known as gravitational mass.

Is gravity needed to measure mass?

• If some known force is applied to a body, and its acceleration is measured, we can calculate the mass using Newton’s 2nd law.

• Since the amount of mass is related to body’s inertia, an how much it resists a change in motion, it is called the inertial mass.