We're talking about two components of momentum that are orders of magnitude different from one another. Imagine a cyclist starting from a dead stop and spinning up to 30kph. How much effort does it take to do that? Let's call it "a lot". He did two things:
1. He got his whole mass moving to the velocity of 30kph 2. He got his wheels spinning to the right speed Whatever "a lot" is, it is the sum of 1 and 2. With me so far? OK, now here's the thought experiment. Put his bike in the stand. Grab a pedal and spin up to 30kph. How much effort did that take? A small child could do it with one hand. You just did #2 above (to the rear wheel) and reduced #1 above to zero. Whatever force it took, It's not "a lot". It's not even 1/10th of a lot. It's tiny. Put on the brakes. Does the wheel gradually slow down? Or does it stop almost instantly? Why is that? Because it doesn't weigh anything. Comparing 200g of tire weight difference is comparing two miniscule forces. Anybody with a powertap rear hub can do that thought experiment in real life. Measure the power it takes to spin up to 30kph. Then do it again with a tire that's 200g heavier. How much difference is it? I don't even know if powertap hubs can measure forces that small. Does the lighter wheel spin up faster and easier? Of course! Could you feel it? Maybe. But both were ridiculously easy in comparison to getting that 100kg mass moving up to speed. Math can't tell you the whole story, but it can get you into the ballpark. The rotational momentum of bicycle wheels is tiny in comparison to the linear momentum of a cyclist in motion. Orders of magnitude. Tell me you've worked up a sweat pedalling a race bike on the workstand. On Thursday, January 2, 2014 6:38:41 PM UTC-8, Benz, Sunnyvale, CA wrote: > > I don't know. Let's do a thought experiment. Let's assume that the wheels > have a very high rotational inertia. Wouldn't that smooth out the sine wave > you're talking about? The slowing down part is when rotational > potential+kinetic energy gets converted to potential energy against > gravity. Using a high rotational inertia will actually help in maintaining > speed (to whatever extent it does) and thus create lower amplitude sine > waves. > > > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/groups/opt_out.
