Really simple gravitational question

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Discussion Overview

The discussion revolves around the concepts of gravitational force, acceleration, and the effects of initial velocity on the motion of falling objects. Participants explore the implications of throwing an object versus letting it fall freely, addressing both theoretical and conceptual aspects of gravity and motion.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether an object thrown from a cliff will fall faster than one simply dropped, seeking confirmation of their understanding.
  • Another participant clarifies that the gravitational force of 9.8 N applies only to a 1 kg mass and that the acceleration due to gravity remains constant regardless of initial conditions.
  • There is a discussion about the distinction between weightless and massless objects, with a focus on how weight and mass interact in different scenarios, such as being in an elevator.
  • Participants note that while both a rock and a feather will experience the same acceleration in a vacuum, the forces acting on them differ due to their masses.
  • One participant expresses confusion about the relationship between mass, force, and acceleration, particularly in the context of gravitational force and external forces.

Areas of Agreement / Disagreement

Participants express differing views on the implications of mass and force in the context of gravitational acceleration. While some agree on the constancy of gravitational acceleration, others raise questions about the nuances of weight and the effects of initial velocity, indicating that the discussion remains unresolved.

Contextual Notes

There are limitations in the discussion regarding assumptions about air resistance and the specific conditions under which the objects are falling. Participants also highlight the need for clarity in definitions related to weight and mass.

Who May Find This Useful

This discussion may be useful for students studying physics concepts related to gravity, motion, and forces, particularly those grappling with the distinctions between mass, weight, and acceleration.

LoveKnowledge
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I seem to be brain dead and I just want to make sure of something (no homework problem). If I am at a cliff and I let an object fall via free fall of course the gravitation force approx. 9.8 N will act on the object. If I give it an initial acceleration or exert a net force, the object will fall to the ground quicker than if I just let the object fall off my hand without that force (for example throwing it) correct? I just seem to be brain dead with the logic of this and it has been stuck in my head for the last few minutes...sorry for such a simple question
 
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First, the force will only be 9.8N if the object has a mass of 1kg. Otherwise, the force will be different.

Second, the acceleration will be the same no matter what you do. However, if you give it some initial downward velocity (such as throwing it), it will reach the ground faster.
 
cjl said:
First, the force will only be 9.8N if the object has a mass of 1kg. Otherwise, the force will be different.

Second, the acceleration will be the same no matter what you do. However, if you give it some initial downward velocity (such as throwing it), it will reach the ground faster.

Since the object is weightless (if thrown down off a cliff) the force would be 9.8N m/s squared regardless wouldn't it? It should depend on the mass at that point...am I getting something confused here?

Of course the acceleration would be the same; I guess the only different would be the initial downward velocity (such as throwing it) but all the other forces such as the force of gravity would be equal since the initial downward velocity (the throw) is an external nonzero net force...so away from that everything equals out but I am just confused as to your initial point as not taking into account air friction...a feather and a rock should fall at the same rate regardless of its mass...
 
A Weightless object and a massless object are two different things. When you are standing in an elevator, your weight is the force exerted by the floor of the elevator upwards so that you don't sink into it. ie the force balancing the force of gravity acting downwards. your mass doesn't change whether you are in free fall or if the elevator is moving up or down, but your weight changes.

The acceleration due to gravity is 9.8 m\s that means that the rock and feather will both experience the same change in velocity over the same period of time neglecting air resistance, but the force on the two are completely different.

To make the rock change it's velocity at the same rate as the feather a much higher force is needed ( F=ma )

The reason the acceleration is the same for both objects is that acceleration is inversely proportional to mass ( a=F\m) but the gravitational force of gravity is directly proportional to the mass! ( F= -Gm1m2\r^2)

so if the mass of one object is double that of the other, it gets accelerated only half as fast by an equal force on the two, but the gravitational force on it is double that of the lighter object.
 
Thanks so much for the explanation. I was just a little confused as I have been studying so many equations in my Conceptuals Physics class lately. Thank you again for the explanation to clarify things for me!
 

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