3.5 newtons laws of motion and momentum

Newton’s First Law

an object will remain at rest or at a constant velocity unless acted upon by a resultant force

Newton’s Second Law

the net force acting on an object is directly proportional to(equals) the rate of change of momentum, and acts in the same direction

F = ∆p/∆t

F = ma

an equation derivable from Newton’s second law, as it can be derived from F = ∆p/∆t

Newton’s Third Law

when two objects interact they exert equal and opposite forces on each other

linear momentum

the vector product of a body’s mass and velocity

p = mv

symbol p, unit kgms^-1

impulse of a force

a measure of change in momentum derivable from Newton’s second law

the product of the force and the time for which it acts

impulse = F∆t

units Ns

alternate impulse equations

impulse = ∆p

impulse = m(v-u) (mass(final velocity - initial velocity))

area under a force time graph

equal to the impulse of the force over that time period

conservation of momentum

momentum is conserved in a closed system, meaning the total momentum of the interacting objects is the same before and after the interaction, including directionally

elastic collisions

-objects colliding do not stick together and then move in opposite directions

-kinetic energy is conserved

inelastic collisions

-objects colliding stick together and then move in the same direction

-some kinetic energy is lost to other forms

conservation of momentum and collisions

for a one-dimensional collision the amount of momentum in either direction is conserved

m1u1 + m2u2 = m1v1 + m2v2

total momentum before the interaction = total momentum after

this still holds true for two and three dimensional collisions, but the extra dimensions must be considered separately