Newton's Laws

Newton’s First Law

A body at rest remains at rest, or, if in motion, remains in motion at a constant velocity unless acted on by a net external force

Newton’s Second Law

The acceleration of a system is directly proportional to and in the same direction as the net external force acting on the system, and inversely proportional to its mass

Newton’s Third Law

Whenever one body exerts a force on a second body, the first body experiences a force that is equal in magnitude and opposite in direction to the force that it exerts

force formula

F=ma, units: N

apparent weight of body in stationary lift

N= mg, units: N

apparent weight of body in lift accelerating upwards

N= m(g+a)

• N > mg, you feel heavier

apparent weight of body in lift accelerating downward

N = m(g-a)

• N < mg, you feel lighter

acceleration of combined contact (pushing) force on blocks

a = F/ (m1+m2+m3)

contact (pushing) force of 1 on 2

F = (m2+m3) a

contact (pushing) force of 2 on 3

F = (m3) a

acceleration of combined contact (pulling) force on blocks

a= F/ (m1+m2+m3)

tension force of string between 1 and 2

F= (m2+m3)a

tension force of string between 2 and 3

F= (m3)a

kinetic friction force

coefficient of kinetic friction by normal force

maximum static friction

coefficient of static friction by normal force