Unit 6/7 - Energy & Momentum

12/4

energy in = energy out (e.g. KE = KE + PE)

• use for things like a dude running then jumping

• conservation of energy

• isolated system (no external forces)

friction =

heat = work

• don’t forget to account for it if it isn’t negligible

if 2 objects have same KE, does the one with larger or smaller mass have more momentum

larger mass has more momentum

if 2 objects have same momentum, does the one with larger or smaller mass have more KE

smaller mass has more KE

for the KE equation, don’t forget

TO SQUARE THE VELOCITY

watch your use of

sin and cos

momentum is a vector

• conserved in the x-direction

• conserved in the y-direction

elastic vs inelastic collision

• equation elastic if KE is conserved

• inelastic if KE ISN’T conserved

impulse depends only on

momentum changes; doesn’t get affected by changing impact time (which just affects the force)

for two objects acting on each other w/o external forces

change in momentum is equal (impulse is equal)
e.g. two people pushing off each other, two balls, etc.

forces on objects come in

equal-opposite pairs

when thinking about momentum

think about adding vectors

• ball bouncing off wall means it has double or more impulse

individual object can’t have 0 KE

if the momentum is also 0

changing speed from 20-30 m/s requires

more work than changing speeds from 10-20m/s

direction of motion of an object can change without

speed changing

if net work = 0 then KE doesn’t change so

speed doesn’t change