Momentum & Impulse: Throwing a Ball at the Wall

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Discussion Overview

The discussion revolves around the application of momentum conservation principles in the context of throwing a ball at a wall. Participants explore the implications of momentum before and after the collision, particularly focusing on the wall's role in the system and the effects of external forces.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions why the principle of momentum conservation (P2=P1) seems not to apply when a ball is thrown at a wall, noting that the direction of the ball's velocity changes.
  • Another participant argues that the wall must be considered as part of the entire system, suggesting that the wall has momentum 2P_1 while the ball has momentum -P_1.
  • A different viewpoint emphasizes that the conservation of momentum applies only in systems without external forces, highlighting that the wall exerts a force on the ball during the collision.
  • Some participants express confusion about how the wall can gain momentum if it remains steady, with one noting that the wall's mass is effectively infinite.
  • Another participant points out that in reality, the wall does not remain steady, implying that external factors may influence the system.
  • One participant elaborates that the wall's momentum should be considered alongside the Earth, as they form a single component of the system, and discusses hypothetical scenarios where a wall not attached to the Earth could behave differently.

Areas of Agreement / Disagreement

Participants express differing views on the wall's momentum and the application of momentum conservation, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Participants highlight the complexity of the system, including the infinite mass of the wall and the implications of external forces, which may affect the conservation of momentum. The discussion remains open-ended regarding these factors.

Who May Find This Useful

This discussion may be of interest to those studying mechanics, particularly in understanding momentum conservation in collision scenarios and the role of external forces in physical systems.

c77793
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Why does the ''P2=P1'' (momentum before is equal to momentum after) isn't applied in cases where u throw a ball at wall?

In this case, even is the velocity keeps the same, it will be in another direction, what makes it -v...
 
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The wall now has momentum 2P_1 and the ball has momentum -P_1. You always need to consider the entire system.
 
The wall has gained momentum(but notice it has no velocity as mass of wall is infinite)

the conservation of momentum applies to systems where there is no external force applied.

if you only consider the ball as system,the wall applies a force on it during collision.
But with ball and wall system the force between ball and wall and vice versa simply become internal forces
 
I just don't get how the wall gain momentum once it stays steady...
 
c77793 said:
I just don't get how the wall gain momentum once it stays steady...

The mass of wall is infinite

So momentum can be finite with even zero velocity

as mathematically, infinite multiplied by zero can be something(finite value)
 
In reality the wall doesn't stay steady.
 
The wall does gain momentum. But really you need to consider the wall and the Earth together because the wall is attached to the earth. This single component of the system has an enormous mass, so its change in velocity is imperceptible.

You can imagine, however, that if a wall is not attached to the earth, and you throw the ball sufficiently fast enough, the wall will totter and fall over. In this case the Earth is not part of the system component.

I think the key realization is that a solid wall is attached to the Earth and these two comprise a single component of the system.
 

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