1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Baseball/tennis ball launchers

  1. Oct 15, 2011 #1
    Why do baseball/tennis ball launchers use two spinning wheels to launch balls, and not one?

    You know, these things:

    Couldn't they replace one of the wheels with a wall?

    I suppose one reason is to eliminate spin, but are there any other reasons?

  2. jcsd
  3. Oct 15, 2011 #2


    User Avatar
    Gold Member

    Spin reduction/control was my first thought, but there might be another stability issue. With only one wheel, the ball might feel obliged to bounce off of the stationary member (rail or chute or whatever). Two wheels keep it airborne.
  4. Oct 15, 2011 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It's spin.

    The goal of a ball launcher is to have an artificial 'sparring partner'. Those wheels rotate so fast that they'd put a completely unrealistic spin on the ball. Even if it made it to the person trying to hit it, it would subsequently careen off in a random direction once it was hit. Not very good to practice against something that a real player could never produce.
  5. Oct 15, 2011 #4
    Thanks, that makes sense. I actually just came across some pictures of machines using only one wheel.

    I am not designing a pitching machine, but something like it. Are there other ways besides reducing friction or adding a non-powered wheel to reduce spin on a one wheel machine?
  6. Oct 15, 2011 #5


    User Avatar
    Gold Member

    The only thing that immediately comes to mind is that you could make a paddle wheel so it slaps the ball rather than rolls it. I'll apply some thought to it, but that's the first thing that leapt out at me.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook