petermarkley
Well-known member
- Joined
- 7 Sep 2024
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Today YouTube recommended this video to me:
After watching, I made this comment under it (pasted below). What do you all think?
My comment:
I think the reason it feels wrong is because we imagine the ball spontaneously moving, but I donāt think thatās what the math describes. Mathematically, for the ball to be at rest and then spontaneously move, it would have to switch states from the rest equation to the rolling equation.
Without external forces (like a tiny vibration or waft of air nudging it) the ball can only ever be in one of the two solutions, not both. If we are observing the ball roll, itās obviously in the rolling case; but if we are observing the ball resting balanced, itās in the ābalanced foreverā case. The existence of the rolling solution does not require that it previously be at rest, unless a negative value for ātā gives a result of zero.
After watching, I made this comment under it (pasted below). What do you all think?
My comment:
I think the reason it feels wrong is because we imagine the ball spontaneously moving, but I donāt think thatās what the math describes. Mathematically, for the ball to be at rest and then spontaneously move, it would have to switch states from the rest equation to the rolling equation.
Without external forces (like a tiny vibration or waft of air nudging it) the ball can only ever be in one of the two solutions, not both. If we are observing the ball roll, itās obviously in the rolling case; but if we are observing the ball resting balanced, itās in the ābalanced foreverā case. The existence of the rolling solution does not require that it previously be at rest, unless a negative value for ātā gives a result of zero.