Physics Help Forum I need a formula for Horizontal force...

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Aug 22nd 2017, 04:15 PM #21 Senior Member   Join Date: Nov 2013 Location: New Zealand Posts: 534 well, you know the distance x2 - x1 and you should be able to work out the initial horizontal component of velocity and this should be constant throughout so its just a matter of working out the time taken for the ball to travel from x1 to x2 (easy once you know the initial horizontal velocity). Then you have to find out what the initial vertical velocity must be in order to go thru (x2, y2) in the same time t. @studiot is calling this impossible, I suspect, because your vertical velocity cannot be an input under the conditions you have supplied as it is dependent upon (x2,y2) and the initial horizontal velocity. It's not independent of horizontal velocity in this scenario but constrained by having to go thru point (x2,y2). If you want your game to work otherwise you need to change the way your game works.
Aug 22nd 2017, 04:16 PM   #22
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 Originally Posted by horrorhippo I am developing a virtual reality baseball game and have batting machines that shoot out balls with a horizontal and vertical force.
If that's what you're doing then I'm unable to help you. When a real bat hits a real ball which results in a particular velocity then its an extremely complicated thing to do. It's not as if we can say "Here. The force horizontally is 12 N" and that's it. It requires knowing what the force is on the ball as a function of time. Then you'd have to integrate that to get the final velocity of the ball. If you ignore drag forces on the ball then the motion of the ball after its hit by the bat will be independent of the mass of the ball and depend only on the velocity.

 Originally Posted by horrorhippo I want to just be able to put in the vertical force (ie how much lob the ball will have) but make sure that the horizontal force is automatically set to always pass through a point above home plate.
Its not possible to state a force which is required to do that since the force of a bat on a ball is a complicated thing and thus its not possible to merely state what force is required. The physics is not that simple. In fact its quite complicated. It depends on the physical makeup of both the bat and the ball since both deform while interacting

Consider this simpler scenario; take a ball and throw it at a wall. The ball will bounce off the wall. The force which acts on the ball is not constant and is a function of the direction of velocity of the ball when it contacts the wall, i.e. it has a specific speed and direction. The wall then starts to deform slightly as the ball hits it and the wall acts back on the ball with a force which may be quite complicated, not a simple constant force.

You won't be able to get what you want because the exact physics of a real bat on real ball is not as simple as you think it is.

If you want to simplify it so that you can determine what force is needed then you need to state what the initial and final velocity is and the time over which the change in velocity too place. Then calculate the change in momentum and divide it by the time it happened.

This website seems to know what its talking about:
https://hypertextbook.com/facts/2000...Klyachko.shtml

You should take a look at it.

This one explains in more detail:
Forces between Bat and Ball

Notice how complicated the force is. It's not a simple force but a force that varies over time resulting in an impulse. That website seems to be a very good one on the subject. Its main website is
Physics and Acoustics of Baseball and Softball Bats

 Aug 22nd 2017, 04:35 PM #23 Junior Member   Join Date: Aug 2017 Posts: 10 To make this even more clear: there is no bat involved in this question whatsoever, its just a ball that is going through the air that needs to pass through a point and it can take as long as it wants.
Aug 22nd 2017, 05:08 PM   #24
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 Originally Posted by horrorhippo To make this even more clear: there is no bat involved in this question whatsoever, its just a ball that is going through the air that needs to pass through a point and it can take as long as it wants.
A ha! Then you don't even need to think about force. If you neglect air drag then the motion is independent of any force other than gravity. The horizontal velocity will remain constant. The motion will also be independent of the mass of the ball. The trajectory is a parabola. If you need help with the math then I'd be glad to lend a hand. If this isn't a homework problem, and its clear to me that it isn't, then I can help you as much as you need and wish.

 Tags force, formula, horizontal