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!

Momentum, Inertia, and Deflection

  1. Jun 21, 2015 #1
    Hi, new here, so I hope I'm doing this correctly. I'll keep this question as brief as possible, but it requires just a bit of setup. I'm not an engineer or physicist, but do have a more than decent layman's understanding. I've lately become fixated on the game of bowling (ten pin), and have found that the ideas and advice commonly shared seem to be based on voodoo and Skittles magic rather than on science. I'm trying to write a small book debunking some of the nonsense, or at least what I believe to be nonsense.

    Without belaboring this, I've calculated that for any given bowler's swing and release (force), a lighter ball will of necessity travel faster than a heavier ball, and hit the pins with more kinetic energy. I've further calculated (I hope correctly) that no matter what weight ball our bowler throws, the Momentum will be the same (lower weight exactly cancelled out by higher velocity).

    I calculated (again, I hope correctly) that if a bowler has enough swing power to propel a 15 pound ball at 16 MPH, he would automatically throw a 12 pound ball close to 20 MPH. While the lighter ball would have more kinetic energy, both balls would have the same momentum. (If you want to see my calculations and my logic, I can link you to the relevant chapter draft) So now (finally!) the questions:

    1. Is it correct (at least colloquially) to say that Momentum can be thought of as the ball's ability to drive through the pins without excessive deflection?

    2. When the ball hits the head pin in some place and at some angle, is it strictly momentum that determines how much the ball will deflect (more momentum = less angle of deflection for any given hit)?

    3. Assuming the above is correct, the lighter ball has less Inertia despite its equal momentum, so why does it not deflect more? I believe this is because momentum is a vector while inertia is not, but I don't know how to explain this in layman's terms.

    Thank you in advance for any guidance you can provide. Also, if anyone with any sort of credentials (and who can look past sometimes gross simplifications, ignoring of proper units, and a "close enough for bowlers" approach to physics) wants to act as fact checker for my chapters, I'd be happy to credit you as technical advisor, and send you copies of the book to impress your mom with (assuming I find a publisher). Besides being a resume stuffer sure to dazzle all seven people I expect to read my book, imagine what an irresistible chick-magnet you will become if you know not only physics, but also bowling! I'd offer you cash, but I'm really not sure if this thing will even sell. It's more a labor of obsession at this point.

  2. jcsd
  3. Jun 21, 2015 #2


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    I think that your statements 2) and 3) conflict with each other. You said in 2) that deflection is a function only of momentum. Then you said in 3) that even though the momentum is the same, you expect more deflection from the lighter ball. Is that conflict what you are asking about?
  4. Jun 21, 2015 #3
    Thank you for the reply, FactChecker. Perhaps my writing wasn't clear. I don't see any conflict between Questions 2 and 3. In question 3, I did not say that I expected to see more deflection from the lighter ball, but rather the opposite. I just said if I am correct in my assumption in Question 2 that it is only the momentum that affects deflection, then how do I explain to a bunch of bowlers why the lighter ball's lesser inertia does not make it deflect more? I speculated that it is because momentum is a vector, so has direction, while inertia just sort of "is", but wanted help in explaining it better.

    Every bowler on the planet thinks that a lighter ball hits the pins with less energy, and deflects more. I contend, and believe I've proved mathematically that ceteris paribus the lighter ball hits with more energy, and deflects to precisely the same degree. It is this that I am trying to confirm.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook