Momentum

September 21, 2010

Momentum

• Linear– A vector that depends on two physical quantities:

the mass and the velocity of the moving object

• Angular– The momentum of a rotating object (not covering

this yet)

• In all cases, momentum is CONSERVED.• FORMULA: p = mΔv

Conservation of Momentum• the total momentum of a closed system of objects is CONSTANT

pi = pf

mΔvi = mΔvf

If there are 2 objects…m1Δvi1 + m2Δvi2 = m1Δvf1 + m2Δvf2

• In collisions, we will have to break down momentum into x & y dimensions

pix = pfx

piy = pfy

Impulse

• An impulse is a force given to an object over a change in time. This impulse changes the objects momentum.– Momentum (our next unit) is found by multiplying

an object’s mass by its velocity

• Impulse = the variable “J”• J = Ft = mv• We need to include impulses in our F

equations

Conservation of Energy• In all processes, energy is conserved

Ei = Ef

• We are going to look at 2 types of energy– Kinetic= the energy of motion= ½ mv2

• Can an object have kinetic energy if it is at rest?

– Potential = the energy of position = mgh

=(mass)(10m/s2)(height)

• If something is at ground level, will it have potential energy?

Ei = Ef

KEi + PEi = KEf + PEf

½ mvi2 + mghi = ½ mvf

2 +mghf