Do objects resist acceleration when falling?

In summary: This resistance applies a force against the accelerating force, which is known as inertia. In this case, the accelerating force is gravity, which means that there is a force against gravity. However, this force is not directly opposing gravity, but rather the force of attraction towards the object's mass. This relationship between mass and gravity was established through experiments, showing that the inertial mass of a body is equal to its gravitational mass. Therefore, the acceleration of a body due to gravity does not depend on its mass. In summary, the resistance to acceleration, known as inertia, applies a force against the accelerating force, which in the case of gravity, is the force of attraction towards the object's mass. This
  • #1
inertiaforce
60
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If I try to accelerate an object to the left, its mass resists that acceleration. If I try to accelerate an object to the right, the same resistance occurs. If I try to accelerate an object forward or backward, the same resistance occurs. This resistance to acceleration is known as inertia.

Gravity is a constant acceleration. If I drop an object, its velocity is constantly increasing under the force of gravity, which means it is constantly accelerating.

Therefore, since it is constantly accelerating, the object's mass should theoretically resist that acceleration the same way it did when it resisted acceleration to the left or to the right or forward or backward.

This resistance to acceleration applies a force against the accelerating force.

Therefore, this means that there is a force against gravity, since gravity is the accelerating force.

Is this correct? Is there a force against gravity?
 
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  • #2
Hey there inertiaforce!

Good point for a new thread and a place to take one step back. At least that's how I felt after reading your post. (LOL)

Gravity originates from mass. The mass you're speaking about has its own gravitational effects on other mass. The gravity you mention might be Earth's, but wherever it also originates from mass.

So if you *really* want to drill into this one :smile:, I'm thinking that the two significant interactions are the two gravitational forces of each mass. Mutual attraction. Each one will affect the other, even though the Earth is awfully large and doesn't show it...
 
  • #3
TumblingDice said:
Each one will affect the other, even though the Earth is awfully large and doesn't show it...

Which just might be a better way to view this. IOW, the Earth would appear to be putting up resistance to the gravitational effect of the mass you spoke of (Object A?).

Must be proportional to mass whether calculated from who accelerates more or who resists more. (6 of one...?)
 
  • #4
inertiaforce said:
This resistance to acceleration applies a force against the accelerating force.

Forget this "resistance to acceleration" and refer to Newtons Laws of motion.
 
  • #5
DrStupid said:
Forget this "resistance to acceleration"

+1.

The basic rule of PF is: this is a site about mainstream physics. If you want to ask questions about Newton's laws of motion, that's fine. If you want to have a historical discussion about what Newton meant by "vis insita" (Principia, definition III) that's also fine - so long as you actually read the relevant parts of Newton's "Principia" first.

But woolly notions of your own about "resistance to acceleration" are something else, IMO.
 
  • #6
inertiaforce said:
If I try to accelerate an object to the left, its mass resists that acceleration. If I try to accelerate an object to the right, the same resistance occurs. If I try to accelerate an object forward or backward, the same resistance occurs. This resistance to acceleration is known as inertia.

Gravity is a constant acceleration. If I drop an object, its velocity is constantly increasing under the force of gravity, which means it is constantly accelerating.

Therefore, since it is constantly accelerating, the object's mass should theoretically resist that acceleration the same way it did when it resisted acceleration to the left or to the right or forward or backward.

This resistance to acceleration applies a force against the accelerating force.

Therefore, this means that there is a force against gravity, since gravity is the accelerating force.

Is this correct? Is there a force against gravity?
The object's mass does not resist acceleration by gravity the same way as the resistance to the left or right forewards or backwards.
You can test this by dropping two objects of different masses they both accelerate at the same rate.
If you take the same two objects and try to accelerate them to the left or right at the same rate they will require a different amount of force, the larger one will require more force to accelerate it at the same rate as the smaller one.
 
  • #7
inertiaforce said:
This resistance to acceleration applies a force against the accelerating force.

Therefore, this means that there is a force against gravity, since gravity is the accelerating force.

Is this correct? Is there a force against gravity?
This is incorrect. As in the previous thread "resistance to acceleration" is mass. Mass does not apply a force against gravity.

For gravity ##F_g=GMm/r^2##. So each mass contributes to the force, it does not oppose it.
 
  • #8
exactly mass attracts all other mass, and the only force that opposes that has to be exerted on the mass which we want to move , because without that force nothing will happen

and inertia works in all frames whether moving something upwards against gravity like a space rocket or when something falls , like a rock from a mountain top.the only difference is in the amount of inertia.which depends on the mass of the object and the velocity.
 
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  • #9
If you are looking for a reactive force to satisfy Newton 1, you can consider the force of attraction, towards your mass, which is acting on the Earth.
 
  • #10
Historically, the following played a role in developing the modern ideas of gravity.

Every body has "gravitational mass". The force of gravity on a body (i.e., its weight) is proportional to its "gravitational mass".

Every body has "inertial mass". The inertial mass resist any force acting on the body; the acceleration is inversely proportional to its "inertial mass".

A series of careful experiments (by Eötvös) established that the "inertial mass"of a body was very accurately equal to its "gravitational mass". Thus the proportionality and the inverse proportionality cancel each other, and the acceleration of a body due to gravitation does not depend on its mass.
 
  • #11
inertiaforce said:
If I try to accelerate an object to the left, its mass resists that acceleration. If I try to accelerate an object to the right, the same resistance occurs. If I try to accelerate an object forward or backward, the same resistance occurs. This resistance to acceleration is known as inertia.

Gravity is a constant acceleration. If I drop an object, its velocity is constantly increasing under the force of gravity, which means it is constantly accelerating.

Therefore, since it is constantly accelerating, the object's mass should theoretically resist that acceleration the same way it did when it resisted acceleration to the left or to the right or forward or backward.

This resistance to acceleration applies a force against the accelerating force.

Therefore, this means that there is a force against gravity, since gravity is the accelerating force.

Is this correct? Is there a force against gravity?

The best way to think about it is that the acceleration is affected by the mass
a=F/m
So the bigger the mass the smaller the acceleration will be for a given force.
In the case of gravity, the force is also proportional to the mass, so the formula for the acceleration has the mass on the top of the formula and also in the denominator. The m's then cancel out and the acceleration due to gravity is the same for all m.
 
  • #12
Buckleymanor said:
If you take the same two objects and try to accelerate them to the left or right at the same rate they will require a different amount of force, the larger one will require more force to accelerate it at the same rate as the smaller one.

The same is true when accelerating under gravity. The larger mass requires more force to accelerate it than the smaller mass.

The only reason two objects of different mass fall at the same exact rate is because the ratio of the gravitational force to the inertia is the same. For example, a penny has little mass, so it has little gravitational force acting on it. That's why it weighs very little. On the other hand, a car has a lot of mass, so it has a lot of gravitational force acting on it. That's why it weighs a lot.

Although the penny has little gravitational force acting on it, it's small mass also has very little inertia, so it is very easy to accelerate. On the other hand, although a car has a lot of gravitational force acting on it, it's large mass also has a lot of inertia, so it is very hard to accelerate. Therefore, the ratio of gravitational force to inertial resistance is the same for every object, and that's why every object falls at the same rate. But the force acting on the larger mass to get it to accelerate is much greater than the force acting on the smaller mass to get it to accelerate.

So when you say "If you take the same two objects and try to accelerate them to the left or right at the same rate they will require a different amount of force, the larger one will require more force to accelerate it at the same rate as the smaller one", this is also true with downward acceleration due to gravity as well. The larger mass will require more force than the smaller one. This is not limited to horizontal acceleration. The larger mass has a much larger accelerating force acting on it even in the downward direction than the smaller mass does. The only reason they fall at the same rate is because the ratio of the accelerating force to the inertia resisting the acceleration is the same. That's why they accelerate at exactly the same rate.
 
  • #13
Guys, let me try to clarify my question.

If you accelerate an object to the left, it will resist your attempt to accelerate it. By resisting your attempt to accelerate it, a force is produced against the accelerating force. This force against the accelerating force is equal in magnitude to the accelerating force and opposite in direction to the accelerating force.

If you accelerate the same object to the right, the same effect occurs, a force is produced equal in magnitude but opposite in direction to the accelerating force. The same thing happens if you try to accelerate the object forward or backwards.

This force that is equal in magnitude and opposition in direction to the accelerating force is produced by the object's mass resisting acceleration (its inertia).

Since the object's mass resists acceleration forward or backward, or left or right, then theoretically, it should also resist acceleration downward.

Since gravity is a downward accelerating force, this means that the object would produce a force equal in magnitude but opposite in direction to the downward accelerating force, the same way it produced a force equal in magnitude but opposite in direction to the leftward accelerating force, rightward accelerating force, forward accelerating force, or backward accelerating force.

Since the downward accelerating force is gravity, this means therefore that the object is producing a force equal in magnitude but opposite in direction to the force of gravity.

Is there such a force, produced by an object's inertia, equal in magnitude but opposite in direction to the force of gravity?
 
  • #14
inertiaforce said:
Is there such a force, produced by an object's inertia, equal in magnitude but opposite in direction to the force of gravity?

This has already been pointed out. There is an equal force on the Earth, upwards,to the force, downwards that is pulling the mass. Because it is so massive, the Earth doesn't move appreciably. If we replaced the force of gravity with a piece of string under tension, the action and reaction forces would be more obvious, perhaps.
 
  • #15
sophiecentaur said:
This has already been pointed out. There is an equal force on the Earth, upwards,to the force, downwards that is pulling the mass. Because it is so massive, the Earth doesn't move appreciably. If we replaced the force of gravity with a piece of string under tension, the action and reaction forces would be more obvious, perhaps.

Ok so the answer is yes? There is a force, produced by an object's inertia, equal in magnitude but opposite in direction to the force of gravity?
 
  • #16
inertiaforce said:
Ok so the answer is yes? There is a force, produced by an object's inertia, equal in magnitude but opposite in direction to the force of gravity?

If you want the answer "yes", then yes, there is.
 
  • #17
sophiecentaur said:
If you want the answer "yes", then yes, there is.

That is amazing.

And what you are saying is that this force, equal in magnitude, but opposite in direction to the force of gravity, pulls back on the Earth then? But because the Earth is so massive, the Earth doesn't move under that force?
 
  • #18
inertiaforce said:
If you accelerate an object to the left, it will resist your attempt to accelerate it. By resisting your attempt to accelerate it, a force is produced against the accelerating force. This force against the accelerating force is equal in magnitude to the accelerating force and opposite in direction to the accelerating force.
It sounds like you are talking about Newton's 3rd law here, not his 2nd law. A 3rd law reaction force acts on a different body, and it is not due to the first body's inertia. It is due to the interaction force between the two bodies.

inertiaforce said:
This force that is equal in magnitude and opposition in direction to the accelerating force is produced by the object's mass resisting acceleration (its inertia).
I have never seen that characterization of the 3rd law. Specifically, I have never heard it as being due to the inertia of the other object. Do you have a reference for this?

inertiaforce said:
Since gravity is a downward accelerating force, this means that the object would produce a force equal in magnitude but opposite in direction to the downward accelerating force, the same way it produced a force equal in magnitude but opposite in direction to the leftward accelerating force, rightward accelerating force, forward accelerating force, or backward accelerating force.
It does. The object pulls up on the Earth with an equal and opposite force to the force of the Earth pulling down on the object.

inertiaforce said:
Is there such a force, produced by an object's inertia, equal in magnitude but opposite in direction to the force of gravity?
No, it is caused by the object's gravity, not its inertia.
 
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  • #19
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.
 
  • #20
DaleSpam said:
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?
 
  • #21
I am :smile:.

Here are some references for each force being caused by gravity:
http://www.school-for-champions.com/science/gravitation_force_objects.htm
http://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation
http://www.regentsprep.org/Regents/physics/phys01/unigrav/default.htm
http://faculty.wwu.edu/~vawter/physicsnet/topics/Gravity/NewtonLawGravity.html [Broken]
http://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#grav

Can you produce any reference that one force is caused by gravity and the other is caused by inertia?
 
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  • #22
It's both gravity and inertia. Take either one away and you have no force.
 
  • #23
DaleSpam said:
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.
 
  • #24
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.
 
  • #25
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.
 
  • #26
sophiecentaur said:
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.
 
  • #27
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?
 
  • #28
voko said:
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".
 
  • #29
TurtleMeister said:
It's both gravity and inertia. Take either one away and you have no force.

This is interesting. Without inertia there is no gravity?
 
  • #30
sophiecentaur said:
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.
 
  • #31
inertiaforce said:
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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1. What is the relationship between acceleration and falling objects?

According to Newton's Second Law of Motion, the acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to its mass. This means that as the force of gravity pulls an object towards the ground, its acceleration increases until it reaches a constant speed known as terminal velocity.

2. Why do objects resist acceleration when falling?

Objects resist acceleration when falling due to the force of gravity acting on them. This force is counteracted by the object's mass, which determines how much resistance it will have to acceleration. Objects with larger masses will have more resistance to acceleration than objects with smaller masses.

3. How does air resistance affect the acceleration of falling objects?

Air resistance is a frictional force that acts in the opposite direction of the object's motion. As an object falls, it experiences an upward force from air resistance that increases as its speed increases. This force eventually balances out the force of gravity, causing the object to reach terminal velocity and resist further acceleration.

4. Does the shape of an object affect its resistance to acceleration when falling?

Yes, the shape of an object can affect its resistance to acceleration when falling. Objects with larger surface areas, such as a parachute, experience more air resistance and therefore have a lower acceleration compared to objects with smaller surface areas, such as a ball.

5. Can an object ever completely resist acceleration when falling?

No, an object cannot completely resist acceleration when falling due to the force of gravity acting on it. However, as mentioned before, the force of air resistance can balance out the force of gravity, causing the object to reach a constant speed known as terminal velocity. At this point, the object is not accelerating anymore but is still falling due to the force of gravity.

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