2.1 - Momentum and energy
● Impulse = ∆ p(change∈linear momentum)=F ∆ t (derived from Newton’s 2nd law of
motion)
t p2
dp
○ ALSO F= , ∫ F dt=∫ dp=p 2− p1=∆ p (= impulse)
dt 0 p 1
●
Momentum p=mv Always conserved Vector, so θ
matters
Energy 1 NOT always Scalar, so θ
KE= m v 2 conserved doesn’t matter
2
2 2
1 2 1 p p
○ p=mv , KE= m v ; p =m v so KE= m 2 =
2 2 2
/¿ (applicable to non-
2 2 m 2m
relativistic particles)
● Elastic collisions: KE conserved, inelastic collisions: KE not conserved (some energy
dissipated as heat due to friction)
1
● Impulse = ∆ p(change∈linear momentum)=F ∆ t (derived from Newton’s 2nd law of
motion)
t p2
dp
○ ALSO F= , ∫ F dt=∫ dp=p 2− p1=∆ p (= impulse)
dt 0 p 1
●
Momentum p=mv Always conserved Vector, so θ
matters
Energy 1 NOT always Scalar, so θ
KE= m v 2 conserved doesn’t matter
2
2 2
1 2 1 p p
○ p=mv , KE= m v ; p =m v so KE= m 2 =
2 2 2
/¿ (applicable to non-
2 2 m 2m
relativistic particles)
● Elastic collisions: KE conserved, inelastic collisions: KE not conserved (some energy
dissipated as heat due to friction)
1
