## Falling in a vacuum

Discussions on classical and modern physics, quantum mechanics, particle physics, thermodynamics, general and special relativity, etc.

### Falling in a vacuum

A large rock and a small rock will fall at the same speed in a vacuum. I find that a hard concept to accept but Galileo said it. So, must be true. Just one question. In a vacuum, will the falls of the rocks - or anything else - be instantaneous? If no kind of force (air, etc.) is restraining them, it seems it might be a pretty fast drop.

Thank you.
vivian maxine
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### Re: Falling in a vacuum

If the two rocs fall on one another, they will not accelerate at the same rate. The moon is less accelerated towards the earth than the inverse, reason why they do not have to travel at the same orbital speed. When the mass of the rocs is negligible compared to a planet, they thus only seem to accelerate at the same rate towards it. Massive bodies accelerate towards one another because of gravitation, and by definition, it takes time to accelerate. For an acceleration to be instantaneous, the force would have to be infinitely strong, which is impossible since there would always be a distance between the two bodies, a distance that would necessarily weaken the force because it is originating from them. Am I right professor?

Now if we extrapolate a bit, when we move a massive body inertially, it also takes time to accelerate, what we call resistance. Could that resistance be partly due to the time it takes for the force to be transmitted? In other words, could mass originate from the transmission gap? Sorry professor, I couldn't resist forcing the gap a bit! :^)

Inchworm
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### Re: Falling in a vacuum

Inchworm » April 14th, 2016, 9:21 am wrote:If the two rocs fall on one another, they will not accelerate at the same rate. The moon is less accelerated towards the earth than the inverse, reason why they do not have to travel at the same orbital speed. When the mass of the rocs is negligible compared to a planet, they thus only seem to accelerate at the same rate towards it. Massive bodies accelerate towards one another because of gravitation, and by definition, it takes time to accelerate. For an acceleration to be instantaneous, the force would have to be infinitely strong, which is impossible since there would always be a distance between the two bodies, a distance that would necessarily weaken the force because it is originating from them. Am I right professor?

Now if we extrapolate a bit, when we move a massive body inertially, it also takes time to accelerate, what we call resistance. Could that resistance be partly due to the time it takes for the force to be transmitted? In other words, could mass originate from the transmission gap? Sorry professor, I couldn't resist forcing the gap a bit! :^)

Inchworm, I am not ignoring you. Mr. MacHQ has been here fixing lots of things on my new computer. That interrupted everything. Now I am trying to understand your reply. One question at a time:

It's the first part I don't understand. Are you disagreeing with Galileo's statement that the rocks will both land at the same time? Actually I was just accepting that he was right and they would fall at the same rate in a vacuum. It wasn't my question but now it is.

As for my question - in a vacuum, will something fall almost instantaneously? - I think you are saying "no" because of a "force". What is this force and is causing resistance - if that is what you mean? I am not too well informed about force.

Thank you.
vivian maxine
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### Re: Falling in a vacuum

vivian maxine » Thu Apr 14, 2016 4:29 pm wrote:Actually I was just accepting that he was right and they would fall at the same rate in a vacuum. It wasn't my question but now it is.
They will both be accelerated at the same rate. Therefore, if they are released at the same time, their speed will always be identical.

vivian maxine » Thu Apr 14, 2016 4:29 pm wrote:As for my question - in a vacuum, will something fall almost instantaneously? -
the moment an object is unsupported, or released then it will begin to fall. That is instantaneous.
Eclogite
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### Re: Falling in a vacuum

Eclogite » April 14th, 2016, 12:49 pm wrote:
vivian maxine » Thu Apr 14, 2016 4:29 pm wrote:Actually I was just accepting that he was right and they would fall at the same rate in a vacuum. It wasn't my question but now it is.
They will both be accelerated at the same rate. Therefore, if they are released at the same time, their speed will always be identical.

vivian maxine » Thu Apr 14, 2016 4:29 pm wrote:As for my question - in a vacuum, will something fall almost instantaneously? -
the moment an object is unsupported, or released then it will begin to fall. That is instantaneous.

I don't mean begin to fall. I mean hit the bottom. Thanks.
vivian maxine
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### Re: Falling in a vacuum

How long they take to fall will depend upon two things: the strength of the gravitational field and the distance they have to fall. Unless the fall distance is infinitely small then the event will not be instantaneous.
Eclogite
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### Re: Falling in a vacuum

Vivian Maxine wrote:As for my question - in a vacuum, will something fall almost instantaneously? - I think you are saying "no" because of a "force". What is this force and is causing resistance - if that is what you mean? I am not too well informed about force.
The force that forces bodies to change direction or speed. If you force a ball to move forward, it forces you to move backward. If you were in space, the ball would get a speed forward, and you would get a different speed backward. How old are you Vivian? Didn't you learn that at school?

Inchworm
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### Re: Falling in a vacuum

Hi Vivian,

If you drop a feather from the same height as a bowling ball on the moon (no air) and they are released at exactly the same time, the feather and ball will land at exactly the same time. The weight doesn't matter. Neither will fall instantly, but rather accelerate over time. On the Earth the acceleration rate is: For every second traveled an object (ball) will pick up an additional 32 feet per second of speed (in a vacuum of course).

So at the end of 1st second the ball is traveling at 32 feet per second. At the end of the 2nd Second just add another 32.. so now it is falling 64 feet per second. At the end of the 3rd Second is it falling at a rate of 96 feet per second.. and so on. This will continue until the object hits something and stops.

This rate of acceleration is dependent on the level of Gravity. So an object on the Moon accelerates more slowly than an object on Earth and an object on Jupiter is about 7 times more than on the Earth.

This all is measured in a Vacuum because air will hinder this acceleration because air has to get out of the way for the object to pass through. You can feel this hindrance by putting your hand out the window of a car traveling at say 60 MPH. A skydiver takes advantage of this by spreading out his limbs and keeping his falling speed around 100 Mph or can maneuver himself into a diving posture, thus reducing his surface area to the thick air and get up to about 170 Mph.

Gravity used to be thought of as a force because it requires a force (push/pull) to be applied to an object to get it to move or change its direction of travel. You still sometimes hear the term "the Pull of Gravity". Well Gravity doesn't pull at all. A gravitational field is required. This field has a Density aspect, a bit like air near the ground is Denser than air above the clouds. It's this difference in Density that causes an object to accelerate towards greater Density. Typically, this Density is called Curvature. The greater the Curvature (density) the faster an object will accelerate on its own.

I could explain why, but that would fall into the category of Personal Theory, which is not entirely forbidden here because no one has a good explanation for exactly how Gravity works. Granted we have tons of great Math that allows us to make perfect predictions about Gravity and Gravitational Accelerations vs. Mass and Distances etc, but no accepted explanation for the Mechanics of Gravity currently exist.

Interesting sidebar note: There is Gravity up in local Outer Space, like around the Space Station.

See.. the Space Station actually is falling, all the time. But it is traveling at high speed roughly parallel to the Ground below. Because the Gravitational Field Density is constant at a constant distance from the Ground, there is no acceleration. And because the Earth is curved, the ground is always tilted away and down such that the falling never gets the Space Station any closer to the Ground. This is called Free-Fall or being in orbit.

If you could run a ladder up to the same height as the Space Station and stood on top the ladder, you would find only about 6 percent of your weight has disappeared due to the distance between you and the Ground.

Note: You will need protection from the environment in outer space and a really, really, really strong guy to hold the ladder ;^P

Hope this helps.

Best wishes,
Dave :^)

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### Re: Falling in a vacuum

Ah, there we are. Gravity is still present even in a vacuum and therein is my problem. Thank you very much, Dave. I do appreciate this.
vivian maxine
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