A collision is an interaction involvinglarge forces acting for a short time.S△t
A collision is an interaction involving large forces acting for a short time. 𝐹 Ԧ 𝛥𝑡
During the short time of thecollision, internal forces aremuch bigger than externalforces.We can ignore the externalforces during the collision
During the short time of the collision, internal forces are much bigger than external forces. We can ignore the external forces during the collision
Momentum principle:4psys =4psys = 0Pf = pi
Momentum principle: 𝛥𝑝 Ԧ sys = 𝐹 Ԧ net𝛥𝑡 𝛥𝑝 Ԧ sys = 0 𝑝 Ԧ 𝑓 = 𝑝 Ԧ 𝑖
Energy principle:4Esys = W4Esys = 0Ef = Ei(Careful-totalenergy isconserved, but the kineticenergy might not beconserved!Somemightbeconverted to heat.)
Energy principle: 𝛥𝐸sys = 𝑊 𝛥𝐸sys = 0 𝐸𝑓 = 𝐸𝑖 (Careful – total energy is conserved, but the kinetic energy might not be conserved! Some might be converted to heat.)
We might still need toaccount for external forcesduring the time before andafter the collision.Example: Gravity, acting onthese two balls, is importantbefore and after theycollide. But during thecollision, we can ignore it
We might still need to account for external forces during the time before and after the collision. Example: Gravity, acting on these two balls, is important before and after they collide. But during the collision, we can ignore it