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!

B Diving for baseballs

  1. May 29, 2016 #1
    From a physics point of view, is there an argument that it is advantageous for an outfielder to dive for a waist high ball rather than attempt to catch it on the run?
  2. jcsd
  3. May 29, 2016 #2

    Charles Link

    User Avatar
    Homework Helper
    Gold Member

    I like to play baseball and find the question quite interesting. When a line drive is coming right at you and is waist high or lower, and sometimes with a pop-up that is dropping in front of you, it seems you can often get a better look at the ball, not by diving, but by dropping to your knees as you make the catch. The biggest factor here would seem that it's easier to catch a ball closer to eye level with the mitt more in front of you. One physics/mathematics explanation is the line of sight angle of the ball doesn't change nearly as quickly when it approaches your mitt if you catch it directly in front of you versus below you or to the right or to the left of you. Even with the pop-up, it's much easier to make the catch closer to shoulder level than to hold the mitt with your arm outstretched in front of you. In the second method, the line of sight angle changes very quickly as the ball goes into your glove.
  4. May 30, 2016 #3


    User Avatar
    Gold Member

    For an infielder, there is a reach that he can do with his gloved hand.
    On the gloved side the reach can be about 3 feet, and for the non-gloved side since the arm crosses the body, about a foot if the player does not twist his body.
    So by standing still in one spot, the player has an area around which he can catch the ball at waist height.

    We will call an area around the player, the GL ( gloved area ) - that area in which the ball is catchable.

    For a motionless blody, the gloved area is justt the area encompassed by the rotation of the gloved arm arounfd its SP (swival point) ie the shoulder.

    One can extend the analysis for body movement, by designating CL ( centerline ) dividing the player from top to bottom into 2 equal halves. The players COM ( centre of mass ) is assumed to lie along this line. The catchable area is asymetric about the CL but should be fairly circular about the SP.

    The player can extend the catchable area by movement of his body, but with his feet still planted to the ground.
    By jumping up, he can catch higher ballls.
    By leaning, he can extend the are horizontally.
    By twisting the body, he can extend the area in which it is possible to catch balls on his non-gloved side..

    By moving his feet, the player can again extend the GL. He can thus move, lean, twist, extend the gloved hand, and maybe jump.
    If he remains upright,
    He can step to the left or right.

    If he leans and steps, ie running,
    he can again extend the GL.

    If he jumps and rotates ( leans excessively ) his body to the right or left, ie diving.
    he can again extend his GL.

    Question is:
    Does the extended GL ( glovable area ) always become greater for each of the outlined cases where the player is making each extra, or different movements?
    ( I haven't listed all the possible cases but the ones I felt led up to the diving case )
    Especially the last two which is of your concern.

    The COM of the player moves when he steps, rotates ( leans ), and possibly when he twists (for the non-gloved side ).
    Accelerating the COM ( centre of mass )of the player , requires forces which have to come from the legs.
    The COM is either translating ( moving to the left or right ), rotating ( following an arc about the feet, or a foot ), or both.

    Some knowledge of kinematics of moving body is need to obtain an answer for the maximum area within which a player can catch a ball.
    As well as, body movements, muscle strengths, ( not physiology - can't think of the term right now ), but one can make some assumptions under the "spherical cow" realm of physics to get a general answer for a general player.
  5. May 30, 2016 #4
    I haven't yet digested all of your response, but my initial question was specifically about an outfielder. I'm thinking of the cases when he runs to the left or right to catch a ball about waist high. It makes the highlight reels but is it really necessary or helpful, compared to just continuing to run toward the ball? I think, generally speaking, the great outfielders of the past didn't dive like they do today.
  6. May 30, 2016 #5

    Charles Link

    User Avatar
    Homework Helper
    Gold Member

    I am an outfielder and I do think it can be helpful on occasion to skip the last stride before catching the ball and essentially gliding and subsequently falling to the knees to have the movement be more steady right before catching the ball on a running catch. Do today's outfielders showboat a little on occasion? It's possible. Diving for a ball is a little risky. At 61 years of age, if the ball is just out of reach, I normally will let it drop in.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted