You can’t bounce a ball under a table

You can’t bounce a ball under a table

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Thanks to Hugh Hunt for the idea for this video.

If you try to pass a bouncy ball under a table, if it hits the underside of the table it will just bounce back out the way it came.

Here’s the golf ball paradox video: https://youtu.be/5sbM2Isx17A
Here’s the turntable paradox video: https://youtu.be/3oM7hX3UUEU
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36 Responses

  1. @SteveMould says:

    Does it make more sense now? Maybe. idk
    The sponsor is Incogni: The first 100 people to use code SCIENCE at the link below will get 60% off: https://incogni.com/science

  2. @JanStrojil says:

    Now explain why the children’s bouncy ball always gets stuck under the sofa and never bounces out.

  3. @aettic says:

    Steve, you are one of the best science communicators I’ve ever seen. So glad that you make these videos. Your kindness and endless curiosity are greatly appreciated.

    • @huuuuuuuuuuuuuuuuuuuuuuuuuuuhn says:

      seriously one of the few channels where whenever I see a video being recommended I cannot resist. It also never feels like a waste of time watching them

    • @jacobshirley3457 says:

      I’d say Steve Mould and ScienceClic are equally good at converting complex topics into something intuitive.

    • @me0101001000 says:

      What I appreciate is that he communicates things in a manner which someone with no background in science can follow, but then an expert can also appreciate the content as well. I’m an aspiring professor of engineering, and Steve’s delivery is something I’ve been paying close attention to so I can be a better teacher.

    • @BloopTube says:

      He nails it on a level that only people like the curiosity show and Bill nye have matched,

    • @anearforbaby says:

      Absolutely true. I have been really disappointed by some other channels losing sight of their purpose, but everything I’ve seen from here remains focused and thoughtful.

  4. @ChrisTooley says:

    I like that you use props like a book and a box – it shows people that they can explore physics with the stuff they’ve already got in their house

  5. @Vlow52 says:

    That’s also related to the “impossible” shots in snooker and other billiard games. When cue ball suddenly reverses its direction due to the spin gripping the cloth or cushion.

    • @cage989 says:

      this is more like a ball coming off the rail with sidespin

    • @Vlow52 says:

      @@cage989 yes, that’s what I’m talking about. If you inspect a masse shots with a lot of spin, it’s essentially the same forces of friction that reverses the direction of the ball after gliding on a flat surface. It’s probably possible to replicated it in 3d by using slippery or magnetic surfaces that ball bounces off, but essentially you can see these effects in games like baseball and golf, when spinner ball runs on curve by catching air molecules.

    • @MikkoRantalainen says:

      The “impossible” snooker shots also use the fact that there’s a difference between static friction and sliding friction. And because change between those happen pretty abrupt when force remaining in the ball decreases (thanks to sliding friction), the ball seems to suddenly change behavior in the middle of the shot which gives the “impossible” appearance.

    • @cage989 says:

      ​@@Vlow52 the cueball slides along the surface before coming back with backspin, it’s not the same as a ball changing direction immediately when coming off a rail with side spin

    • @trajectoryunown says:

      Does that include making the ball jump as well?

  6. @flyingdev says:

    I bet if you did this demonstration with a ball covered in different coloured spots you’d get a nice visual indication of the change in rotational axis after each collision. The various spots would move more or less depending on how close to the axis they are and after a bounce a different spot would stop moving

  7. @mrWade101 says:

    As someone who plays table tennis, this is very intuitive but incredible nonetheless.

    • @lanzer22 says:

      Exactly what I was thinking. Receiving a top spin always makes the ball want to bounce up, etc.

    • @martinda7446 says:

      Try it with a bouncy ball… You will do some ”impossible” shots. I was wondering about the extreme lightweight smooth ping pong ball… I bet that will bounce under a table.

  8. @MrPibi says:

    I love how well you keyed out your hand on that slo-mo shot, what an editor!

  9. @loveme-Or-Hateme says:

    Very interesting. Wonder how it would go if the surfaces provided a “less than near elastic collision”. Like ultra high density foam or rubber “plates”. With less perfect elastic restoration, higher drag/friction, and dampening, would it then become a “never exits” as opposed to “always exits”?

  10. @Lombardio says:

    “Low-poly cylinder” is my new favorite name for convex regular polygons.

    You brought up friction at the collisions, but I kept wondering if you were going to address deformation of the ball at each bounce. My initial thought is that the ball deforming when it hits a surface mostly just increases the surface area for friction to be applied, but I don’t know enough about bouncy ball physics to decide if it is a crucial part of the dynamics or not.

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