http://www.ck12.org Chapter 4. Motion and Forces
4.25 Mass vs Weight
- Define weight.
- Show how to calculate the weight of an object from its mass.
This is Sam at Newton’s Skate Park. He’s standing on the back end of his skateboard to keep it from tipping over the
edge of a half-pipe. The force of his weight pressing down on the skateboard prevents gravity from pulling it over
the edge and down the side of the half-pipe.
Weight, Mass, and Acceleration
Weightis a measure of the force of gravity pulling down on an object. It depends on the object’s mass, which is how
much matter the object contains. It also depends on the downward acceleration of the object due to gravity, which is
the same all over Earth. Weight can be represented by the equation:
F = m×a
This is the general equation that relates force to mass and acceleration. When it relates weight to mass and
acceleration, the letter F represents the object’s weight in Newtons (N), which is the SI unit for weight. The letter
m in the equation represents the object’s mass in kilograms, and the letter a represents the downward acceleration
due to gravity. As this equation shows, weight is directly related to mass. As an object’s mass increases, so does