Physics question... (WARNING: Science content)

[sloth_mobile]

So, I'm sitting down at Shari's with eyeamme123  and we start getting into a deep physics discussion on how bicycles work....

The scenario:
If someone who was pedaling at maximum speed on a road-bike (the one with the thinner tires with the bigger circumference) with a very light frame on a flat surface, would the output of energy they'd have to create all of

Comments

[sloth_mobile]

you're right...

I *did* forget to add those circumstances into the equation. I guess it's hard how to describe yourself doing something you're really really into to somebody who only has a vague idea of how to do that same thing.

It's like me trying to explain to you how to sweep pick on a guitar (an advanced method of fast guitar soloing that very few novice players can actually really learn) when you've just barely learned how to do basic chord figures...

[sloth_mobile]

Should have mentioned other circumstances:

Sitting upwards will cause you to naturally have a lower maximum speed... not only because your posterior has full contact with the seat (and more energy output in your leg muscles because there's less gravity from your body to push down on the pedals), but also because it will also create drag, due to wind resistance. That's why anybody who's trying to ride at maximum speed will pitch forward, lifting most of their weight off the seat, mainly because there's less wind resistance that's causing you to slow down. The more surface area that you have exposed, like your upper torso creates the wind resistance... but when you have it pitched forward, more wind will go over your back, similar to a reverse effect of Bernoulli's Principle.

[theevil_chie]

I'll be the first to admit that physics isn't a science I know much about, but I had a good laugh at "WARNING: Science content" XD

[fearless_son]

It is not so much a question of gravity as inertia, and not a question of speed as acceleration.

That is, to maintain the same acceleration at different states of mass, one would have to put more energy into the motion at the larger state of mass than at the smaller state of mass to maintain the same acceleration.

Either way the bike and rider would have the same theoretical top speed, but assuming a constant input of energy in both mass states, the less massive state would reach that top speed more quickly than the more massive state.

[fearless_son]

Well, while you are at it, it would be better to clarify the distinction between mass and weight. Mass is a measure of how much "stuff" there is in a give system. "Weight" is how much force gravity puts on a mass, being expressed as Weight = Mass * Gravity. Now the standard measure of gravity is "G" defined as the gravitational strenght of the Earth at sea level being a single G. This means that, in most on-Earth contexts, mass and weight can be used interchangable (since anything times one equals itself) but it is good not to get in that habit too much