# Do objects resist acceleration when falling?

by inertiaforce
Tags: acceleration, falling, objects, resist
 P: 731 There's nothing special about gravity in this respect. Try working with two objects of less extreme mass difference and you can understand it better.
P: 37
 Quote by DaleSpam It is caused by the object's gravity, not its inertia.
When I asked sophiecentaur the question "There is a force, produced by an object's inertia, equal in magnitude and opposite in direction to the force of gravity?"

Sophiecentaur responded with "If you want the answer "yes", then yes there is."

Now you're saying no there isn't. You're saying it's caused by the object's gravity.

So who's right lol?
 Mentor P: 16,306 I am . Here are some references for each force being caused by gravity: http://www.school-for-champions.com/...ce_objects.htm http://en.wikipedia.org/wiki/Newton'...al_gravitation http://www.regentsprep.org/Regents/p...av/default.htm http://faculty.wwu.edu/~vawter/physi...awGravity.html http://hyperphysics.phy-astr.gsu.edu...grav.html#grav Can you produce any reference that one force is caused by gravity and the other is caused by inertia?
 P: 731 It's both gravity and inertia. Take either one away and you have no force.
P: 37
 Quote by DaleSpam No, it is caused by the object's gravity, not its inertia.
But gravity doesn't require the object to be accelerated.

The force I am talking about only occurs when a force attempts to accelerate the object.
 Sci Advisor PF Gold P: 11,142 Could we please not use the word 'inertia' in any explanation as it has no precise definition. Why can't we use the word Mass, which we all agree about? Earth has mass and produces a force on another object with mass. This force (due to gravity) also acts on the Earth only in the opposite direction. These two forces seem to satisfy the requirements for a Third Law Pair. When the 'object' is as big as the Moon, the force on the Earth is large enough to cause a measurable wobble in the Earth's path round the Sun.
 Thanks P: 5,473 All this talk of "inertia" makes very little sense. It is not well defined - in fact, it is simply not defined! - in modern physics. We do have terms like "moment of inertia" and "inertial frame" - but these terms are very well defined, while "inertia" per se is not. So we cannot say "caused by inertia" because we would not understand what we really mean by that. Any two interacting bodies are acted upon by equal forces of opposite directions. Historically, this is what Newton's third law states. In modern view, we analyze interaction through potential energy of interaction, and that automatically results in Newton's third law as a geometrical consequence. "Inertia", whatever that means, is not required for that.
P: 37
 Quote by sophiecentaur Could we please not use the word 'inertia' in any explanation as it has no precise definition. Why can't we use the word Mass, which we all agree about? Earth has mass and produces a force on another object with mass. This force (due to gravity) also acts on the Earth only in the opposite direction. These two forces seem to satisfy the requirements for a Third Law Pair. When the 'object' is as big as the Moon, the force on the Earth is large enough to cause a measurable wobble in the Earth's path round the Sun.
I would prefer to use the word "mass" sophie. But when I used the words "mass resists acceleration", people jumped on me for using words like "resistance to acceleration" lol.
 Sci Advisor PF Gold P: 11,142 Resistance implies energy loss. Reaction is a better word and it is used in the Third Law. Why not write the sentence using the word Reaction and no one could moan?
P: 37
 Quote by voko All this talk of "inertia" makes very little sense. It is not well defined - in fact, it is simply not defined! - in modern physics. We do have terms like "moment of inertia" and "inertial frame" - but these terms are very well defined, while "inertia" per se is not. So we cannot say "caused by inertia" because we would not understand what we really mean by that. Any two interacting bodies are acted upon by equal forces of opposite directions. Historically, this is what Newton's third law states. In modern view, we analyze interaction through potential energy of interaction, and that automatically results in Newton's third law as a geometrical consequence. "Inertia", whatever that means, is not required for that.
My understanding of the definition of inertia is "resistance to acceleration".
P: 37
 Quote by TurtleMeister It's both gravity and inertia. Take either one away and you have no force.
This is interesting. Without inertia there is no gravity?
P: 37
 Quote by sophiecentaur Resistance implies energy loss. Reaction is a better word and it is used in the Third Law. Why not write the sentence using the word Reaction and no one could moan?
Well the reaction is producing a resistance isn't it lol? The reaction force is synonymous with saying a resistance to acceleration.
Mentor
P: 16,306
 Quote by inertiaforce But gravity doesn't require the object to be accelerated. The force I am talking about only occurs when a force attempts to accelerate the object.
There is no such force.

This thread has really degenerated and is closed.

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