What is the answer to this physics riddle?

  • Thread starter Thread starter micromass
  • Start date Start date
  • Tags Tags
    Physics Riddle
Click For Summary
The discussion revolves around the physics of two balls traveling along different paths from the same height to a lower height, focusing on the time taken to reach the finish line. Participants debate the implications of frictionless conditions and the shapes of the paths, with references to the brachistochrone problem, which identifies the fastest path between two points under gravity. Key points include the importance of the path's slope and curvature, as well as the initial velocity of the balls. It is noted that while the potential energy at the start and finish may be equal, the time taken can differ significantly based on the path's shape. The conversation highlights that not all paths below a flat trajectory are guaranteed to be faster, and specific calculations are necessary to determine which path is optimal. The discussion concludes that while some paths may be faster, the relationship between height, velocity, and distance is complex and requires careful analysis.
  • #31
Borek said:
Then how come brachistochrone exists, if time on all curves is identical?
But it isn't one. The more on kinetic energy gained downwards is lost again upwards. (But I haven't done the math, maybe it doesn't cancel out, however I think it does. I desperately try to remember the analogous experiment in a math museum I once visited, I thought they were equally fast at the finish ...)
 
Physics news on Phys.org
  • #32
fresh_42 said:
But it isn't one. The more on kinetic energy gained downwards is lost again upwards. (But I haven't done the math, maybe it doesn't cancel out, however I think it does.)

The final speed must be the same (without friction) but the ball will take different times for different paths. For example, you can have a path with a time to the lowest point as large as you wish!
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 10 ·
Replies
10
Views
2K
Replies
2
Views
3K
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 16 ·
Replies
16
Views
5K
  • · Replies 9 ·
Replies
9
Views
1K
Replies
35
Views
7K
Replies
25
Views
4K
  • · Replies 1 ·
Replies
1
Views
3K