Physics of Thrown Baseball: Air Resistance & Gravity Forces

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Discussion Overview

The discussion centers on the forces acting on a thrown baseball, specifically examining the roles of air resistance and gravity throughout its motion. Participants explore the dynamics of the baseball's trajectory, particularly at the moment it leaves the hand and at the peak of its flight. The conversation includes theoretical considerations and practical implications of these forces.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that after the baseball leaves the hand, both the weight of the ball and the force from the hand act on it initially, but later only gravity acts on it.
  • Another participant counters that after the ball leaves the hand, only gravity and air resistance act on it, emphasizing that air resistance must be negligible for the trajectory to resemble an upside-down parabola.
  • A participant questions the role of the hand's force, noting that once the hand is no longer in contact with the ball, it cannot exert a force on it.
  • It is mentioned that the hand applied force changes the ball's momentum, but does not influence it after release.
  • One participant explains that at the top of the baseball's motion, gravity and aerodynamic forces are continuously acting on the ball, with gravity being a constant force and aerodynamic forces varying with conditions.
  • Another participant emphasizes that nothing special occurs at the top of the arc to cause the ball to fall, reiterating that the hand does not impart forces once it is no longer in contact with the ball.
  • A later reply clarifies that gravitational force acts on the ball throughout its flight, slowing its upward motion until it reverses direction, and that a force is not needed to maintain constant velocity.

Areas of Agreement / Disagreement

Participants express differing views on the influence of the hand's force after the ball is thrown, with some asserting it continues to act while others argue it does not. The discussion reflects multiple competing perspectives on the forces involved in the baseball's motion, indicating that consensus has not been reached.

Contextual Notes

Some participants assume negligible air resistance for their arguments, while others highlight its variability. The discussion also touches on the distinction between force and momentum, which may not be fully understood by all participants.

cristina
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What forces act on a thrown baseball?

(Assuming the baseball motion is an upside down parabola). What forces act on a thrown baseball? 1) After the first fraction of second after it leaves your hands? 2) After it leaves your hands and at the top of it motion (top of the parabola). Some people think that the force of the hand continues to act throughout the motion. Other think that the only force acting throughout the motion is force of gravity. Who is correct from an experiment point of view?

I think after the few fractions of the second when the ball leaves the hand, there is the ball’s weight acting on it, and the force of the hand. At the middle of the parabola there is only the weight = mass x (9.81 m/s^2) acting on it. what about the air?. From an experience point of view I think that they are both wrong, that hand force act on the ball at the beginning of its motion and after the hands force fades the gravity force takes over.
Am I correct?
 
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I'm sorry but you aren't.
After the ball has left your hand, only gravity and air resistance will act on it (although for the trajectory to take the form of "an upside down parabola" the air resistance must be negligeble).
 
What about the froce of the hand?
 
If your hand is not touching the ball, how can it be applying a force on it? YOu are confusing "force" with "momentum." Your hand applied force in order to chage the ball's momentum. After it leaves your hand, the ball continues with its momentum, but your hand no linger has any influence on it.

Well, technically, there is a gravitational force from your hand, but its way too small to measure.
 
What is happening at the top of the baseball's motion for the baseball to fall down? Can someone give me a complete answer instead of frangments please, how should I understand the concept otherwise?
 
Last edited:
Originally posted by cristina
What would happen at the top of the baseball's motion for the it to fall down? Can someone give me a complete answer instead of frangments please, how should I understand the concept otherwise?
Its pretty simple: two forces act on the baseball at all times after it has left your hand and until it hits the ground: gravity and aerodynamic. Gravity is a constant force and aerodynamic changes with changes in speed, rotation, and the properties of the air during the flight. Nothing at all special (new) happens at the top of the arc to make the ball start coming back down.

The others are correct: if your hand is not touching the ball, it is not imparting any forces on it.

Sometimes its tough for us to answer questions because we need to understand what you are saying first and we're not speaking the same language. Science has its own language. Perhaps if you elaborated on the specific nature of your question it would help us help you.
 
Originally posted by cristina
What is happening at the top of the baseball's motion for the baseball to fall down? Can someone give me a complete answer instead of frangments please, how should I understand the concept otherwise?

Assume for simplicity that the air resistance is negligeble.
After the ball has left your hand only the gravitational force will act on it, trying to pull it back against the earth. Since the ball prior has been given an upward motion (by the force from your hand!) the effect of the gravitational force is to slow that motion down until the ball turns, and then pull it back to the earth.
It is exactly the same force acting on the way up as on the way down!

What I think you may not have understood is that a force is NOT needed to make an object move with constant velocity. A force changes the objects velocity (i.e it accelerates the object)!
For example if you are throwing a ball somewhere out in space far away from any large masses, the ball will keep on going with the same velocity as it had when it left your hand since no forces will act on it...

If you want to understand this better I suggest you read about Newton´s laws. Anyone who has a good link?
 

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