Transcript Momentum

Linear Momentum
Law of
Conservation of
Momentum
• This is one of four conservation laws in physics that are
very important (charge, energy, and mass also)
• We will only study linear momentum (angular momentum
is an AP Physics C topic only)
• Useful to use for interactions (like collisions)
Momentum and Its Relation to
Force
• Momentum is the product of an object’s mass
and velocity
– p  mv
– Units of kg∙m/s
• Momentum comes from Newton’s Second Law
• The rate of change of momentum (derivative of
momentum) is equal to the net force acting on it
Conservation of Momentum
• momentum before = momentum after
• The total momentum of an isolated system of
objects remains constant
• System = set of objects chosen that interact with
each other
• Isolated = the only significant forces are
between the objects in the system
– i.e., there is no net forces acting on the system
• Often occurs in explosions
Collisions and Impulse
• Impulse = the product of force and the time over
which the force acts
• J  Ft
• Impulse is the area under an F-t curve
Conservation of Energy and
Momentum in Collisions
• Elastic Collision = total kinetic energy is
conserved
• Inelastic Collision = energy is conserved,
but is no longer kinetic
1-D Collisions
• Elastic Collisions
vA1  vA2  vB1  vB 2
• Inelastic Collisions
• True for explosions,
or where friction is
present
• If it is completely
inelastic, the objects
will stick together
Collision in 2-D or 3-D
• Momentum in each direction is conserved
– px is conserved, py etc.