More momentum?
Wouldn't the same be true of a vertical drop? And we know that doesn't help.
A bobsled is accelerated by human effort, so more weight means more mass to accelerate to a higher momentum that would then maintain speed longer against friction slowing it down. But that's just my 2c. I'm not a physicist.
Suppose we had a flat stretch of ice, two sleds with different weights, and two machines set to give each an identical push towards the finish line. (I think this is a fair analogy to the bobsled acceleration, since the push the sledders give to the heavier sled would be equal to the push they'd give to the lighter sled: in each case, they will be giving it all the force they can.) If more mass -> greater momentum -> longer period at high speed vs. friction, then we would expect the heavier sled to reach the finish line first, wouldn't we? But that can't be right, because then a sled weighed so heavily that the machine could barely get it started would also finish first.
I would expect some trade off in terms of the extra effort needed to get the extra mass moving. As well as not being a physicist, I'm also not a bobsled competitor, so I have no idea whether extra weight is desirable, or at what point the extra weight makes it too hard to accelerate the sled. But the OP is right about gravity, so added momentum is the only thing that would make sense to me.
Imagine a sled as light as a feather. The force given it is constrained by the speed at which the crew can run. Conversely a sled weighing a ton would be constrained by the strength of the crew getting it moving. The optimum weight is where both strength and speed are maxed out. I'm not sure what the regulations are, but a fixed weight means that all variations in speed are down to the physical capabilities of the crew. (ignoring all the other design constraints). The question is surely, does the medal go to the fastest strongest crew, or the cleverest designer?
But aren't they maxed out in both scenarios? The crew will give all the leg-force it can for both the feather-light sled and the one-ton sled. (In both cases, at least as it appears from the little bobsledding I've seen, the arms do little but hang on.)
I don't know the regulations either, but there are sports in which design advantages can be critical. (Race car driving, for example. The best driver in the world won't win with an inferior car.)
It just occurred to me that if extra weight in the sled were an advantage, shouldn't extra weight in the crew be as well? Wouldn't two heavyweight bobsledders then have a big advantage over two lightweights?
They do. That's why they are built like brick sh1thouses.
Maybe it would help if we broke the acceleration here down into horizontal and vertical components.
I expect the extra muscle mass would be more valuable for getting the sled going at the start, but the limitation is that they all have to fit in a very cramped space quite quickly once moving.
For the horizontal component, friction counts in the tight turns so that is where extra mass/momentum might help.
Probably why they tend to be built like rugby players rather than sumo wrestlers.
But extra momentum on a tight turn would mean more inertia, thus taking the sled off course, wouldn't it?
I agree.
You're right. The definitely helped me
Okay, at this point I have to admit that I assumed that cheating by adding extra weight is actually a thing here. My belief was based solely on the movie Cool Runnings, where the John Candy character had been suspended for doing just that previous to the movie. In retrospect, using a John Candy movie as the basis for my belief might not have been the wisest move (much as I like John Candy). But who new that a movie might include something that's not actually true?
"Dynamic positioning of mass" means that the crew lean in on curves. In yacht racing, crewmen are picked for their size because they can then affect the stability by moving about. Ask AN for further details.
On the general topic of sports and physics, I remember once hearing Erich Segal (author of Love Story, but also a classics professor) commenting on the Olympics and saying that the ancient Greek long jumpers would carry a couple of lead weights and then throw them behind them when they were in mid-air, giving them a kind of "rocket" type boost. And I thought, wait a minute... wouldn't the extra weight handicap their liftoff at least as much as the discard would help them? If that sort of thing could work, couldn't you use the same principle to create a perpetual motion machine? So was Segal botching the physics, or was I missing something?