10 terms

# Mass, weight, and normal force

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Mass
A measure of the amount of matter in an object
Weight
A measure of the force of gravity on an object
kg (kilogram)
SI unit for mass
N (Newtons)
SI unit for force (and, therefore, weight, since weight is a force)
Formula to calculate weight from mass
F = mg
Normal Force (Fn)
The perpendicular force exerted by a surface on an object in contact with it; this force prevents objects from pushing through the surface; on a flat surface, it counteracts gravity/weight.
Formula for normal force on a flat surface
Fn = -Fg = -mg
Why is there a negative sign in the normal force equation for an object on a flat surface?
On a flat surface, the normal force counteracts gravity (weight). It is equal in magnitude but is upward, not downward, so we need to multiply weight (which is negative) by -1 to make it positive.
What does g stand for?
g stands for the acceleration due to gravity (-9.81 m/s^2)
Does g stand for gravity?
Nope! g stands for the acceleration due to gravity.