W=mg
W= weight
m = mass
g = freefall acceleration
Units: newtons (N)
What is this person's weight on
Earth?
W=mg
W = (80.0 kg)(9.80 m/s^2 )
W = 784 N
5.5 - Newton’s second law
Newton's second law: “A change in motion is proportional to the motive force
impressed and takes place along the straight line in which that force is
impressed.”
Newton stated that a change in motion (acceleration) is proportional to force. Today, physicists call this Newton’s second law, and it is stated to
explicitly include mass. Physicists state that acceleration is proportional to the net force on an object and inversely proportional to its
mass.
To describe this in the form of an equation: net force equals mass times acceleration, or ȈF = ma. It is the law. The Ȉ notation means the
vector sum of all the forces acting on an object: in other words, the net force. Both the net force and acceleration are vectors that point in the
same direction, and Newton’s formulation stressed this point: “The change in motion...takes place along the straight line in which that force is
Newton’s second law
Net force equals mass times
acceleration