Angular momentum (Why is the whole universe spinning????)

I know momentum is talking about the energy of moving objects. I know a large truck has more momentum than a small car and that a fast car has more than a slow car so I really don’t want to get in the way of a large truck that is speeding. The bigger and faster, the more wallop!

linear momentum = mass (weight) x velocity (speed)

So angular momentum is similar but for rotating or spinning objects. Instead of the mass, it uses the inertia of the object (how much it does NOT want to change). If it is whizzing round or getting more compact, it wants to keep whizzing. If it is dawdling in a huge orbit, it resists any change to that orbit.  And the circular speed is called the angular velocity.

angular momentum = inertia (resisting change) x angular velocity (circling speed)

Angular momentum is interesting because it is a vector. That means it has a magnitude (SIZE) and a direction (CIRCULAR) whereas momentum only acts in the straight line direction of travel. Moreover, angular momentum is important because it is conserved in a closed system, that is, it has to stay the same. A tiny bit of maths here tells me that to conserve angular momentum (keep it the same), any increase in inertia (forcing a change in mass or direction) will result in a decrease in angular velocity (slowing down) and vice versa.

Maths Moment:   A = B x C   means when B increases, C must decrease

Angular momentum in action

Have you noticed that it is harder to balance on a slow-moving bike than when it is moving more quickly? As the wheels speed up, they decrease inertia by not wanting to change direction and so they stay more balanced. Slowly rotating wheels wobble and veer all over the place much more easily as they are allowing a lot more change; that’s low inertia.

Skaters seem to be superhuman when they dramatically spin faster just by bringing their arms in. That action reduces their inertia by making the body more compact and reluctant to change direction, thus requiring a faster speed to keep the angular momentum the same. It’s simply a law of physics.

Almost everything in the universe spins. We have seen how each planet rotates about its axis, stars spin around black holes and galaxies spin in gigantic spiral designs. We know that spinning cosmic dust and debris is the starting point for building a solar system like our own. The conservation of angular momentum law dictates that when mass moves closer together, it must spin faster. In other words, as those clouds of dust collapse into clumps under gravity, even the tiniest rotational movement must be magnified, and so on ad infinitum.

So this does prove Professor Cameron’s point in the October 2024 talk that it is indeed angular momentum, and not love, that makes the world go round!