Our Reaction is Kind of Like This: Our Reaction is Kind of Like This: Imagine a bug…flying very fast…and there’s a garbage truck sitting there…that our bug crashes into!!!

Oddly enough, the bug and garbage truck are gone…a dump truck & smallelectric car appear in the wake…And they drive off into the sunset!

MakeMakeSense!?Sense!?

Unlikely… but if it did happen, what Unlikely… but if it did happen, what physics rules must be followed? physics rules must be followed?

1.Conservation of momentum (pbefore = pafter).2.Conservation of energy (KEBUG = KEdump + KEcar).2A. Conservation of energy & mass (E = mc2).

Conservation of Momentum RestrictionsConservation of Momentum Restrictions

For each axis pbefore = pafter

pbug + pgarbage = pdump + pcar

Momentum Before the CollisionMomentum Before the CollisionA 0.0001 kg bug is flying at a speed approaching light speed (3.0 x 108 m/s) and crashes head on into a 16,000 kg garbage truck at rest.

pbefore = pbug + pgarbage

pbefore = (mv)bug + (mv)garbage

pbefore = 0.0001kg(3 x 108 m/s) + 0

pbefore = 30,000 kg.m/s

The truck is not moving. This term = 0.

In the axis of the bug’s motion.

Momentum After the CollisionMomentum After the Collision

p = 30,000 kg.m/s x-axis only

(py) truck

(px) truck

(px) car

(py) car

(px)car + (px)dump = 30,000 kg.m/s

(py)car + (py)truck = 0 kg.m/s

Initial SystemMomentum

What changes if…What changes if…

• the garbage truck idles and randomly rocks the garbage truck idles and randomly rocks back and forth before the collision?back and forth before the collision?

•Initial py varies moment to moment.

•Typically, the initial py ≠ 0 kg.m/s.•After collision y-axis momenta won’t cancel.

p+

-

n0

……Our Reaction is Really More Like Our Reaction is Really More Like The Simulated Model BelowThe Simulated Model Below

neutrino + neutron proton + muon

+ n0 p+ + -

udd uud

p+

-

n0

An extra dimension of space =

…… which is in which is in 3-D! 3-D!

an extra dimension of FUN!

(pz) + (pz)n = (pz)p + (pz)

(px) + (px)n = (px)p + (px)

(py) + (py)n = (py)p + (py)

Neutron at Rest

Let’s welcome the z-axis.Let’s welcome the z-axis.

= (pz)

= 0

= 0

z-axis