Throwing a Softball: Examining Momentum and Gravity

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Discussion Overview

The discussion revolves around the biomechanics of throwing a softball, specifically examining the concepts of momentum and gravity as they relate to the ball's trajectory. Participants explore the implications of throwing the ball at different angles and how forces like air resistance and gravity affect momentum.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether a softball loses momentum to gravity when thrown straight up, noting that gravity does not move away from the ball.
  • Another participant clarifies that the momentum of the ball is not conserved due to the forces of air resistance and gravity acting on it.
  • This participant explains that while the ball loses momentum, the Earth gains momentum due to the gravitational interaction, although the change in the Earth's velocity is negligible due to its large mass.
  • A later reply confirms understanding of the concept, acknowledging that the Earth gains momentum as the ball falls back, but at an infinitesimal rate due to its mass.

Areas of Agreement / Disagreement

Participants generally agree on the interaction between the ball and the Earth regarding momentum transfer, but the initial question about momentum loss to gravity remains open to interpretation.

Contextual Notes

The discussion does not resolve the nuances of how momentum is defined in this context, particularly regarding the effects of gravity and air resistance on the ball's motion.

Who May Find This Useful

Students and educators interested in biomechanics, physics of motion, and the principles of momentum and gravity may find this discussion relevant.

jhale18
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I have just begun a biomechanics unit in Year 9 Phys ed, and have received my assignment for the term. As part of the assignment we must consider the momentum of the ball and its forward trajectory. I didnt place this thread in homework, as there is no actual problem, just considerations. On aspect of biomechanics we must explain is throwing a softball, and the angle at which it is released. The main determining factor as to the distance which can be achieved by the throw, is gravity. My question is, if you threw the softball straight up, like 90 degrees to the horizontal, its momentum will be conserved moving the air around it with air resistance and all, but does the ball lose momentum to gravity? If so, how, as gravity does not move away from the ball, although the Earth does?
 
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jhale18 said:
My question is, if you threw the softball straight up, like 90 degrees to the horizontal, its momentum will be conserved moving the air around it with air resistance and all, but does the ball lose momentum to gravity? If so, how, as gravity does not move away from the ball, although the Earth does?
The momentum of the ball is not conserved since there are forces acting on it. Both air resistance and gravity.

I think you are saying that as the ball collides with the air, the total momentum of air and ball is conserved. Good! The same thing happens with gravity and the earth. The ball and the Earth exert equal and opposite gravitational forces on each other. So as the ball loses momentum, the Earth gains momentum. (Since the Earth is so vastly bigger than the ball, its tiny change in velocity is unmeasurably small.) The net change in momentum of ball and Earth due to gravity is zero.
 


Cool, I can understand that. So as the ball falls back towards the earth, the Earth can be seen to be gaining momentum, but due its extreme mass, acclerates at an infinitesimal rate. I hope I got that right. Thanks very much.
 


Exactly.
 


Cool, thanks.
 

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