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by taeric 2383 days ago
Yeah, and we have words for that. Momentum, is a good one.

I should clarify the last time I had this conversation, I'm talking about 40+ year olds building bikes. They were thinking a heavier bike would accelerate faster down a hill. That just is not how that works.
1 comments
isidor3 2383 days ago
It actually is though! The force due to air resistance is the primary thing slowing down the bike and rider, and the force, which doesn't change with mass, slows down a heavier bike less, and so a heavy bike will be rolling faster than a lighter one at the bottom of a hill, all other things being equal.
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taeric 2383 days ago
Right, you can hit a higher velocity. You will not get extra acceleration. That is my entire point.

That is to say, the force from the air does not actively slow you down. It prevents you from speeding up, after a point. (Aerodynamics are, of course, more complicated. But this general model is pretty solid.)

Such that if I want to accelerate faster down the hill, I have to pedal to cause that to happen. Or add a motor.

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jstanley 2383 days ago
The heavier bike will reach the terminal velocity of the lighter bike sooner than the lighter bike will. If that's not extra acceleration then I don't think you're looking at the problem from a practical perspective.

Yes, acceleration due to gravity is the same, but air resistance has less effect, at all speeds, on the heavier bike. The rate at which the heavier bike gains speed is higher. It accelerates faster.

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taeric 2382 days ago
This is just disagreement over magnitude. And what it means to hit higher acceleration.

Take my statements to be, it won't hit a meaningful higher acceleration. Not that it won't necessarily accelerate for longer.

In general, you will accelerate down the hill at 9.8 m/s^2 modified by the incline. No matter how heavy the bike is. (Within the realm of realistic weights.).

Yes, the points you are raising are true. But within the realm of the biker and realistic bikes, not really relevant.

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SirLuxuryYacht 2382 days ago
The velocity of the bike+rider is proportional to their mass. Realistically this can range over two orders of magnitude, which can be particularly relevant in a racing context.
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taeric 2382 days ago
I'm intrigued. What are you saying here?
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