How do i define angular momentum for rigid bodies?
I cant really explain it to myself while i understand the concept
In: Physics
imagine a strongman at the circus. He picks up a bowling ball and spins it on the tip of his finger, as if it was a basketball. Then he sets down the bowling ball and picks up a barbell with weights on it, balances it on his finger the same way, and spins it like he did with the bowling ball. The barbell and bowling ball weigh the same, but he finds it much harder to start and stop the barbell. This is because the weights on the barbell are further from his finger, and so they act like a lever. The weight in the bowling ball is closer to the finger, so it acts like a lever too, but a shorter one, and a longer lever (like a pry bar) makes the dumbbell act stronger than the bowling ball.
IIRC Angular momentum is about the momentum of something attached to the end of a ‘lever’ or ‘pry bar’, so it acts stronger. Because the weight is attached, the weight can’t fly off, so the attachment (bar of barbell, for example) holds it in like a dog running in circles on a leash.
From this you could figure out why a wide flywheel wants to keep spinning at the same speed, where a narrower flywheel would be easier to speed up or slow down.
Spinny thing will stay spinny unless you apply torque to it. Just like moving thing will keep moving unless you apply force to it.
The farther out the mass of the thing is from the rotation axis, the harder it is to change how fast it spins. This “how hard is it to change its spinning” is the moment of inertia. Think of it like what the mass is to linear movement.
Just like normal momentum is velocity * mass, angular momentum is now angular velocity * moment of inertia.
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