Ch+6+-+Momentum

Chapter 6 Impulse and Momentum sum of the Forces = ma F = m(change in velocity/change in time) F(change in time) = mass(change in velocity) F(change in time) = M(Vfinal - Vinitial) F(change in time) = mVf - mVi Momentum - Linear momentum is the product of the mass of an object and velocity of the object, p

=m**v** units= kg m/s = Ns

Can a rollerskate and Mack truck have same momentum? Yes - fast roller skate, slow truck, or both objects at rest

Newton's 2nd Law F(change in t) = mVf - mVi F(change in t) = Pf - Pi = F(change in time) = change in p)

How do you change the momentum of an object? apply a force for some time

Newton wrote - sum of forces = (change in p) / (change in t) Rate of change (t) of momentum of an object is equal to net force acting on the object

Impulse - J J = F(change in t) Force acting through some time units: kg m/s = Ns

Momentum Theorem J = F(change in t) = change in p = mVf - mVi How do you increase momentum? increase mass or velocity, apply more force or time

Applying Impulse - Momentum - tennis, golf, other sports - How do you want to stop a car out of control? brick wall or haystack? - catching a ball - karate

(change in p) = F(change in t) if longer time, then smaller force If a a\greater force is applied for a short amount of time, the greater the momentum than if time was extended with a smaller force

(change in p) = m(change in velocity) greater velocity, then greater momentum

Pelton Wheel(paddle wheel) curved paddle, water bounces off, greater force, turns faster F-t Graphs area under Force - Time graph represents Impulse = Change in momentum

Conservation of Momentum In the absence of an external force, the momentum of a system remains unchages(isolated systems)

sum of p//initial =// sum of p//final// p1i + p2i = p1f + p2f m1v1i + m2v2i = m1v1f + m2v2f An object with a greater mass will travel slower after the collision than an object of lower mass

explosions = initial momentum = 0 because at rest same momentum, opposite direction examples: gun-bullet, person-canoe

Collisions Inelastic - objects stick together, momentum is conserved Elastic - objects bounce off each other, momentum is conserved, KE is conserved Perfectly Inelastic - objects stick together and move off with a common velocity
 * Momentum always conserved

air track demos equal mass, one glider at rest switch velocities unequal mass, one glider at rest inelastic - equal mass, equal but opposite velocities double the mass, half the velocity

Relative Velocity Equation (Elastic Equations Only) v1i - v2i= v2f - v1f