Some confusion about balanced forces

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Discussion Overview

The discussion revolves around the concept of balanced forces when an object falls to the ground. Participants explore the mechanics of forces acting on the object, particularly the relationship between gravitational force and the normal force exerted by the ground or a surface like a trampoline. The scope includes conceptual clarification and technical reasoning regarding forces during impact.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that for an object to stop upon hitting the ground, the ground must exert a force greater than the object's weight.
  • Others argue that the forces acting on the object (gravity and normal force) are equal only under specific conditions, such as when the object is not accelerating.
  • A participant questions the source of the "extra" normal force needed to stop the object, seeking clarification on its origin.
  • It is suggested that the normal force arises from the collision between the object and the ground, with the ground's material structure allowing it to exert an upward force.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the forces involved during the impact. While there is some agreement on the need for the normal force to exceed the weight of the object to stop it, the discussion remains unresolved regarding the source of this additional force.

Contextual Notes

There is a lack of consensus on the conditions under which the forces are equal and the implications of the normal force exceeding gravitational force. The discussion does not clarify the mathematical details or assumptions underlying these claims.

ViolentCorpse
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Hi,

My question is:

1)When an object falls to the ground, shouldn't the ground exert a force greater than the weight of the object to stop its motion altogether? Because if the forces experienced by the object the moment it strikes the ground are equal and opposite in direction, then that should only stop the object from accelerating further and it should continue moving with the velocity it had the instant before the forces cancelled. (I know it sounds silly for the ground because it's a solid, rigid body and can not allow the object to continue its motion through it. Maybe it'd be better if you replace the ground with a trampoline and explain it for that? )

Thank you for your time. :)
 
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ViolentCorpse said:
Hi,

My question is:

1)When an object falls to the ground, shouldn't the ground exert a force greater than the weight of the object to stop its motion altogether? Because if the forces experienced by the object the moment it strikes the ground are equal and opposite in direction, then that should only stop the object from accelerating further and it should continue moving with the velocity it had the instant before the forces cancelled.
Your thinking is quite correct. In order to stop the object, the force from the ground must be greater that the object's weight. (At least for some time.)

Why do you think that is a problem?
 
Doc Al said:
Your thinking is quite correct. In order to stop the object, the force from the ground must be greater that the object's weight. (At least for some time.)

Why do you think that is a problem?

Oh, I'm sorry I didn't make myself clear enough.

The problem is, I don't understand where that greater force comes from.

According to my understanding, The forces on the object are gravity (downward force) and the normal force of the ground (upward) and I think they are equal. But as you just confirmed, the normal force must be greater than that with which gravity is pulling the object. I'm just unable to pin down where that extra normal force is coming from.

Thank you for your prompt reply, Doc Al!
 
ViolentCorpse said:
According to my understanding, The forces on the object are gravity (downward force) and the normal force of the ground (upward) and I think they are equal.
They are only equal under certain circumstances. Such as when the object is no longer accelerating.
I'm just unable to pin down where the normal force is getting that extra force from.
That "extra" force comes from the collision of the moving object with the ground. The material structure of the ground allows it to resist the movement of the object by exerting an upward force on it.
 
Doc Al said:
They are only equal under certain circumstances. Such as when the object is no longer accelerating.

That "extra" force comes from the collision of the moving object with the ground. The material structure of the ground allows it to resist the movement of the object by exerting an upward force on it.

Hm. I see.

Thank you for your help! I appreciate it a lot. :)
 

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