So I saw this gif the other day, and was wondering, is this real or fake? And supposing there is no energy dissipated by the friction, why does such thing occur?


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    $\begingroup$ Why would you think it is fake? What sort of explanation do you expect? The relation between the shape of a curve and how fast things move along it under gravity is not very intuitive, see e.g. brachistochrone problem $\endgroup$ – ACuriousMind Feb 1 '17 at 23:17
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    $\begingroup$ note, the ball on the bumpy track does not reach the same peak altitude at the far side as the ball on the straight track does. The ball on the bumpy track lost more energy to friction (the track is longer!). So you cant really ignore friction. I believe the way to analyze this is look at the energy. In baseball the rule: keep your eye on the ball. In physics: keep your eye on where energy flows. $\endgroup$ – docscience Feb 2 '17 at 1:13
  • $\begingroup$ Related : What is the position as a function of time for a mass falling down a cycloid curve? $\endgroup$ – Frobenius Feb 2 '17 at 9:27
  • $\begingroup$ Possible duplicate of Ball on a slope with hollow. $\endgroup$ – sammy gerbil Feb 3 '17 at 19:49

Can't say I've done anything as drastic as calculate anything, but a quick intuition for why this might work is to consider all the "free" travel the middle section of the bumpy track gives you.

When the ball rises over the top of the first bump it gets to fall a long way (and speed up again !) and this gives it another gravity boost. So it has a couple of those and gets some extra energy.

All the flat surface gets is those tiny little ramps on the end.

Even though the bumpy path is longer, it's also faster (maybe).


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