Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum  2Likes
Aug 21st 2017, 05:55 AM

#1  Junior Member
Join Date: Aug 2017
Posts: 10
 I need a formula for Horizontal force...
Hello,
I'm trying to find a formula to calculate the horizontal force needed of a ball with mass m, that passes through a point [x,y] in 2dimensions. The point is d distance away and the vertical force (fVertical) is also known (and gravity is acting upon the ball at 9.807 m/sē).
To reiterate,
 We know: fVertical, d, g, m, and point [x,y]
 We want: fHorizontal
Thanks!

 
Aug 22nd 2017, 01:49 PM

#2  Physics Team
Join Date: Apr 2009 Location: Boston's North Shore
Posts: 1,195

Originally Posted by horrorhippo Hello,
I'm trying to find a formula to calculate the horizontal force needed of a ball with mass m, that passes through a point [x,y] in 2dimensions. The point is d distance away and the vertical force (fVertical) is also known (and gravity is acting upon the ball at 9.807 m/sē).
To reiterate,
 We know: fVertical, d, g, m, and point [x,y]
 We want: fHorizontal
Thanks! 
We're not allowed to give solutions to problems, only help you arrive at the solution yourself. Otherwise we run the risk of doing people's homework for them.
I'd be glad to give you a hint though. You don't need a horizontal force in order for the ball to pass through (x, y), i.e. it can be zero. So its not clear what it is you want or are really trying to solve. If you told us where this problem comes from we can help you find what you're looking for.

 
Aug 22nd 2017, 02:32 PM

#3  Junior Member
Join Date: Aug 2017
Posts: 10

Originally Posted by Pmb We're not allowed to give solutions to problems, only help you arrive at the solution yourself. Otherwise we run the risk of doing people's homework for them.
I'd be glad to give you a hint though. You don't need a horizontal force in order for the ball to pass through (x, y), i.e. it can be zero. So its not clear what it is you want or are really trying to solve. If you told us where this problem comes from we can help you find what you're looking for. 
I am developing a virtual reality baseball game and have batting machines that shoot out balls with a horizontal and vertical force. 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.

 
Aug 22nd 2017, 02:42 PM

#4  Senior Member
Join Date: Nov 2013 Location: New Zealand
Posts: 519

Originally Posted by Pmb I'd be glad to give you a hint though. You don't need a horizontal force in order for the ball to pass through (x, y), i.e. it can be zero. So its not clear what it is you want or are really trying to solve. If you told us where this problem comes from we can help you find what you're looking for. 
We don't? Is the ball being hit vertically downwards only? Unless I am misunderstanding the problem it would seem that the bat imparts an initial momentum to the ball in the vertical and horizontal direction. However gravity only acts downwards and not horizontally. I assume no other forces.

 
Aug 22nd 2017, 02:45 PM

#5  Junior Member
Join Date: Aug 2017
Posts: 10

Originally Posted by kiwiheretic We don't? Is the ball being hit vertically downwards only? Unless I am misunderstanding the problem it would seem that the bat imparts an initial momentum to the ball in the vertical and horizontal direction. However gravity only acts downwards and not horizontally. I assume no other forces. 
The ball is being shot out of a machine towards home plate. I have complete control over the vertical and horizontal forces being applied but want to make sure that no matter what vertical force value I enter, the ball also passes through point [x,y] which is over home plate.

 
Aug 22nd 2017, 03:02 PM

#6  Senior Member
Join Date: Nov 2013 Location: New Zealand
Posts: 519

Originally Posted by horrorhippo The ball is being shot out of a machine towards home plate. I have complete control over the vertical and horizontal forces being applied but want to make sure that no matter what vertical force value I enter, the ball also passes through point [x,y] which is over home plate. 
Won't the vertical force just be the force of gravity (mg) and therefore a constant? So that would just leave the horizontal force being an input wouldn't it?

 
Aug 22nd 2017, 03:05 PM

#7  Senior Member
Join Date: Apr 2015 Location: Somerset, England
Posts: 688

Originally Posted by horrorhippo The ball is being shot out of a machine towards home plate. I have complete control over the vertical and horizontal forces being applied but want to make sure that no matter what vertical force value I enter, the ball also passes through point [x,y] which is over home plate. 
You may have control of the forces, but your question is impossible to answer.
This is because you don't need to know the forces to achieve your objective.
What you need is the initial velocity and angle of elevation of projection.
This will enable the calculation of the vertical and horizontal momenta required to achieve your objective.
The said momenta can be achieved by a variety of forces, which I presume are what are known as impulsive forces.

 
Aug 22nd 2017, 03:05 PM

#8  Junior Member
Join Date: Aug 2017
Posts: 10

Originally Posted by kiwiheretic Won't the vertical force just be the force of gravity (mg) and therefore a constant? So that would just leave the horizontal force being an input wouldn't it? 
I'm applying a vertical force upwards so that the ball lobs, then gravity will naturally be applied to it (using the physics engine). I need to know the horizontal force given the vertical force so that it passes through point [x,y].
I had a diagram but it didn't post for some reason...

 
Aug 22nd 2017, 03:12 PM

#9  Senior Member
Join Date: Nov 2013 Location: New Zealand
Posts: 519

Originally Posted by horrorhippo I'm applying a vertical force upwards so that the ball lobs, then gravity will naturally be applied to it (using the physics engine). I need to know the horizontal force given the vertical force so that it passes through point [x,y].
I had a diagram but it didn't post for some reason... 
Then as @studiot pointed out you need to know the initial velocity of the ball imparted by the bat. That can be deduced from knowing the force of the bat and the length of time the bat makes contact with the ball. If that's more detail than you're working with then the initial velocity of the ball would suffice. Either way we need more information about the initial conditions of this problem.

 
Aug 22nd 2017, 03:15 PM

#10  Senior Member
Join Date: Apr 2015 Location: Somerset, England
Posts: 688

I'm applying a vertical force upwards so that the ball lobs, then gravity will naturally be applied to it (using the physics engine).

Applying a vertical force ? How? By tying it to Saturn C rocket?
If you would like to reply to my previous post you could get some real help.

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