Thread: Falling Objects in A Vacuum

A lot of people know of the experiement where two objects are dropped from an equal height while inside of a vacuum chamber. Regardless of the mass, size and shape of the objects the objects fall at the same rate which is approx 9.8m/s.

Excluding the apparatus variables, such as the the size of the chamber, or the height the objects are dropped from, there are four variables relating directly to the objects themselves: mass, size, shape, and *temperature*.

My question is:

Has anyone ever found any reference to anyone testing how the fourth variable; by dropping objects of equal mass, size, and shape with one cooled and one heated so as to be at vastly different temperatures; effects the rate at which the objects fall, if at all?

I can only find reference to experiments that alter the first three variables: mass, size, and shape -- but all of them completely ignore the temperature of the objects. I can't find any references to experiments where the fourth variable is tested.

And just to clarify, I'm interested in knowing whether or not anyone has ever ACTUALY TESTED THIS, NOT whether or not people think it will or will not have an effect, regardless of what physics theory states.

I would do the experiment myself, but currently do not have the required tools available to do so.

I'm very interested in knowing if anyone can answer this question.

Thanks,

Rai

How do you think temperature influences the acceleration of an object in vacuum. There's no convection and no bouyancy in vacuum. Do you assume if there's a sgnificant influence. I remember there was one of the astronauts from Apollo XV or XVII that dropped a hammer and a feather on the moon. This looks pretty impressive as it goeas against anything you have experienced so far. This was during the lunar day, so I guess this takes care of the temperature thing. This was just a show experiment, no data recorded as far as I know.

The point is that what you or I think is irrelevant. Unless those specific circumstances have actually been tested experimentally, we have only conjecture and assumption as to the results. I'm asking what the demostrated results of such an experiment have been, if it has actually been tested.

Rai

A very intersting question. I am not aware of any such test. I suspect that it has been tested, but not within the last two centuries. Finding reports on the experiments will be difficult and the rigour of the experimental method may also be highly questionable.
I would be amazed if any influence of temeprature was found, but you are absolutely correct that that has nothing to do with what would actually be revealed by carrying out the experiment.

The closest experiment I can think of is Crooke's radiometer. It doesn't involve falling objects, but it does demonstrate that a heated object in a hard vacuum does not appear to behave differently from a cool object, but this is only when the temperature difference is relatively small. (In a Crooke's radiometer with only a partial vacuum the result is different, because different effects are acting.)

Post-googling correction – there is an effect, due to photon reflection, but it’s extremely small. In the case of uniformly heated objects the photon emission would be equal from all sides so there would be no net thrust. An object heated more on one side would experience a reaction from the emitted photons so its velocity would be affected, (but this is only a thought ).

that that has nothing to do with what would actually be revealed by carrying out the experiment.

Ophiolote, surely it is much more than likely that the exact results could be predicted by what we know about the laws of physics. Galileo did not drop his balls off the Leaning Tower, he did a thought experiment which proved to be right.

Originally Posted by Bunbury

Ophiolote, surely it is much more than likely that the exact results could be predicted by what we know about the laws of physics. Galileo did not drop his balls off the Leaning Tower, he did a thought experiment which proved to be right.

I think the point that rai.auge is making is that science should not be dictated by assumptions. I would happily bet £5,000 that temperature would have no effect. I would not however bet more than this.
Science advances by making surprising discoveries; by people asking strange questions, to which the answer is thought to be obvious - after all, the expected answer matches the laws of physics as we understand them, why should we even investigate. In 99.999% of cases there will be no surprise. Ah, but the wonder of that remaining 0.001%.

If hot bodies behaved differently than cold bodies then the orbits of bodies around the Sun wouldn't behave the way that they do. As it is, we can use the same laws of gravity to predict Venus' orbit as we do to predict Pluto's and get equally accurate answers.

I'm still trying to figure out the most effective way to communicate a light mood through text without resorting to smiley faces (which I must admit have been a crutch I've relied on for several years at the expense of my writing skill). So please don't think I'm all serious and haven't a smile on my face when I say this, but...

...what you or I think is irrelevant. Anything other than a direct observation of the described experiment is nothing more than conjecture or assumption no matter how much theory or math seems to support it. This is the exact opposite of what I'm trying to accomplish -- which is to find out the results of an experiment that would be very simple for anyone with the correct equipment to carry out.

Knowledge comprises of known fact, not postulated theory. Facts are direct observations of events that take place in the real world. So far as I can tell, based on the demostrated experimental evidence, this is known fact:

Objects within a vacuum, dropped from equal distance from the earth will fall at the same rate of accelaration regardless of size, shape, or mass.

Thus, until I can find any demostratable experimental evidence (ie observed results) that shows how the fourth variable of temperature effects this specific experiment, if at all, as far as I can tell the effect of this variable on this specific experiment is still unknown regardless of how many other theories exist or how temperature effects *other* experiments.

It actually suprises me though, as it would be expected that in the interest of being thorough *someone* must have tested this. If not just for the heck of it.

So can anyone find any instance where this experiment was conducted using objects of equal mass, size, and shape but vastly different temperatures? I still haven't been able to.

Cheers,

Rai

The answer to your question is no, simply because temperature has no bearing on gravitational acceleration.

• * F is the magnitude of the gravitational force between the two point masses,
  * G is the gravitational constant,
  * m1 is the mass of the first point mass,
  * m2 is the mass of the second point mass,
  * r is the distance between the two point masses.

Note: There is no temperature variable anywhere in this equation. This, by the way, is observed in nature every day. Yes, I know it's the classical model, but is sufficient in this case.

Thought experiment:

Imagine two balloons. One filled with nitrogen gas, one filled with an equal amount of liquid nitrogen. Despite the considerable volume gain of the first balloon (relative to the second), both would still accelerate equally (in a vacuum).

It's not a hard concept to grasp.

If you're still hell-bent to prove centuries of Physical "Theory"; Try it with two water bottles, and some frozen water (in one). Be sure to stand under them for a more 'intuitive' experience when they're released.

I think the point that rai.auge is making is that science should not be dictated by assumptions. I would happily bet £5,000 that temperature would have no effect. I would not however bet more than this.

What part of the Theory of Gravity, and General Relativity would you consider an assumption? There are many people that bet their lives on these "assumptions".

Yes, science is advances by making surprising discoveries; by people asking strange questions, to which the answer is thought to be obvious. However, these people, also take the time (and respect) to learn the fundamentals...

Originally Posted by spirytus

The answer to your question is no, simply because temperature has no bearing on gravitational acceleration.

This is true only according to theory based upon observation, said observation at no time examining the effect of temperature. This is circular reasoning par excellence. I am disturbed that no one else seems able to grasp the fundamental point that rai.auge is making.

Originally Posted by spirytus

Imagine two balloons. One filled with nitrogen gas, one filled with an equal amount of liquid nitrogen. Despite the considerable volume gain of the first balloon (relative to the second), both would still accelerate equally (in a vacuum).

It's not a hard concept to grasp.

And would you direct us to the published results of this experiment. If you cannot you are merely arguing that if conventional physics theory is correct that this must be the case. rai.auge is, quite correctly, saying 'show me'. From his(her) comments he has little doubt that temperature has no effect. He simply wishes to know, has this ever been experimentally demonstrated?

Originally Posted by spirytus

If you're still hell-bent to prove centuries of Physical "Theory"; Try it with two water bottles, and some frozen water (in one). Be sure to stand under them for a more 'intuitive' experience when they're released.

I think you meant to type disprove, rather than prove. If so, this is not what rai.auge is trying to do.

After somebody tests the effect of temperature, then maybe they should paint the objects green or yellow and see if that does anything. Then they should try it at the North Pole and see what that does.

The point is that what you or I think is irrelevant. Unless those specific circumstances have actually been tested experimentally, we have only conjecture and assumption as to the results. I'm asking what the demostrated results of such an experiment have been, if it has actually been tested

If you are interested to know if such an experiment has ever benn conducted then the answer is: Not to my knowledge. But I still would like to know what you think about this and what makes you assume (not believe) that T actually has an influence.

Originally Posted by rai.auge

...what you or I think is irrelevant. Anything other than a direct observation of the described experiment is nothing more than conjecture or assumption no matter how much theory or math seems to support it. This is the exact opposite of what I'm trying to accomplish -- which is to find out the results of an experiment that would be very simple for anyone with the correct equipment to carry out.

Janus is correct - we don't need to do this experiment in a lab because nature has already helpfully set up the experiment for us. If temperature changed the behavior of falling bodies, then Pluto (which is around -230 C) would behave differently than Mercury (which is around 180C). Since they seem to obey the same orbital dynamics, we can be pretty sure that temperature doesn't change anything for an object in freefall.

Originally Posted by Scifor Refugee

Janus is correct - we don't need to do this experiment in a lab because nature has already helpfully set up the experiment for us. If temperature changed the behavior of falling bodies, then Pluto (which is around -230 C) would behave differently than Mercury (which is around 180C). Since they seem to obey the same orbital dynamics, we can be pretty sure that temperature doesn't change anything for an object in freefall.

So you wouldn't want to explain the anomalous behaviour of Mercury's perhelion shift as being a temperature effect then. Much better to continue with the circular reasoning.

Originally Posted by Scifor Refugee

Janus is correct - we don't need to do this experiment in a lab because nature has already helpfully set up the experiment for us. If temperature changed the behavior of falling bodies, then Pluto (which is around -230 C) would behave differently than Mercury (which is around 180C). Since they seem to obey the same orbital dynamics, we can be pretty sure that temperature doesn't change anything for an object in freefall.

Ohooooooo.....let's not even go down this road. I mean there's discussion about the diameter of Pluto (poor li'l thing got demoted from planet to planetoid already) let alone the exact position. This is not even known with enough accuracy to find small deviations for Mercury. And with small I mean minute effects besides the motion of the perihelion. Messenger will hopefully change this. If you want to have exact data you need to controll the environment before you can prove or exclude any possible influence of other parameters. And if there is an influence of temperature I'd suppose it'll be rather small.

So you wouldn't want to explain the anomalous behaviour of Mercury's [perihelion] shift as being a temperature effect then.

Correct; No I wouldn't bother, because it's already been predicted by General Relativity, and proven by radar observations over ~ 30 years. Look it up.

It actually suprises me though, as it would be expected that in the interest of being thorough *someone* must have tested this. If not just for the heck of it.

I’m surprised you're surprised. The equipment needed would have to be sensitive, since the effect if any would be small. If it weren’t small it would already be known. The experiment would be difficult and expensive, not simple and cheap. If it were done cheaply the results would be in doubt, which is why I wouldn’t bet any money at all on it.

I think you’re wrong about how science proceeds. Harold has already summed this up succinctly, but perhaps his message was too subtle. First comes a hypothesis. There’s little point in doing experiments just because the experiment hasn’t been done before. You should have an idea of what you’re looking for, not just a thought that there might be something. A good example is the search for the Higgs boson. Without it the standard model is incomplete (wrong even – I don’t know) so it’s worth looking for and spending millions of dollars on the search. There’s no theory that says hot objects behave differently under gravity than cold ones so no one’s going to bother testing it.

I do agree about trying to keep things light hearted. Absent body language and facial expressions, things can be misconstrued, as I know from experience.

Yes, but there seems more to it than strikes the eye. There is still some doubt about the accuracy and as long as those still exist the jury is still out. I don't say that the explanation from GR is invalid, but those have to be verified by more data from Messenger. Most of the effect (probably all of it) can be explained with GR though.

Originally Posted by spirytus

Correct; No I wouldn't bother, because it's already been predicted by General Relativity, and proven by radar observations over ~ 30 years. Look it up.

But again you miss the point. General relativity is one explanation for a series of observations. It fits the facts. So did the epicycles of the Earth centred universe. rai.auge wishes to establish whether or not the effect of temperature on gravitational attraction has ever been experimentally assessed. If it has not, that is an omission, pure and simple.

And science does not begin with hypotheses, necesssarily, it can begin with observation. Temperature is an important gross property. Definitely worth investigating in relation to gravity. Investigate it now - I rather think not - but it should have been investigated at some point.

Originally Posted by Ophiolite

Originally Posted by Scifor Refugee

Janus is correct - we don't need to do this experiment in a lab because nature has already helpfully set up the experiment for us. If temperature changed the behavior of falling bodies, then Pluto (which is around -230 C) would behave differently than Mercury (which is around 180C). Since they seem to obey the same orbital dynamics, we can be pretty sure that temperature doesn't change anything for an object in freefall.

So you wouldn't want to explain the anomalous behaviour of Mercury's perhelion shift as being a temperature effect then. Much better to continue with the circular reasoning.

No, you wouldn't. In order to explain the shift of Mercury's perihelion through temperature difference you have to assume that it is the temperature difference between Mercury at perihelion and Mercury at aphelion that causes the effect. But the difference in Mercury's temp at these distances are much smaller than say, the difference in temp between Mercury and Mars. If the perhelion/aphelion temperature variation were enough to cause such a measureable effect, then you would see a much larger effect between Mercury's and Mars' orbit. Large enough that Kepler's laws of planetary motion wouldn't even come close to holding true.

Another example of nature doing the experiment for us is the Jovian system. dozens of satellites with every temp. from geologically active Io to frozen balls of ice and rock. All of them nicely follwing Kepler's laws.

I think the fundamental problem of this thread is the confusion of the word "Theory" with the word "Assumption".

Theory is not merely a conceptual idea that happens to neatly explain natural phenomena. Technically, at its inception, yes, but than as it matures - withstanding the constant assault of experimentation/observation, it becomes a hard concrete building block which than is used as a foundation to younger theories.

In the end, all of Physics is just a Theory. Would that than make it a one giant Assumption? By your reasoning; Perhaps. And so, as scientists, shall we spend our lives questioning all of the fundamental blocks that make up Physics? Or accept them to be relatively accurate and move forward?

Simply put, our lives are finite and as such certain concessions need to be made. If we are to make any headway in our lifetime, we need to accept the knowledge passed down by our predecessors, trust their methods, and plow forward. Should we, in our journey, find any new reason as to question their previous discoveries, only that should we stop, ask the questions how/why, and repair any damage it has caused.

Based on my knowledge, I don't see any reason as to how or why Temperature (color, and/or infinite amount of other insignificant variables) will effect our fundamental understanding gravity. No such reason was given and I hope I've clearly explained why nobody bothered ( among others).

epicycles of the Earth centred universe

This was before the scientific method was established. That, indeed, was an assumption not so much based on observation, but divine belief and political censorship. Its contradiction would likely mean excommunication or even death.

I think we're long past that point.

Originally Posted by Ophiolite

I think the point that rai.auge is making is that science should not be dictated by assumptions. I would happily bet £5,000 that temperature would have no effect.

Originally Posted by Ophiolite

I am disturbed that no one else seems able to grasp the fundamental point that rai.auge is making.

The point is transparent enough but you under-estimate the odds. Theories are the basic tools which scientists use for their trade and they routinely bet far more than a measly £5,000 on the predictions of these theories. Given such an opportunity I would bet everything I have. A sure thing like this just doesn't offer itself everyday. You must remember that many of the laws of physics themselves have a probabilistic foundation. 10^100 to 1 against is an accepted scientific definition of impossiblity.

Correct me if I am wrong (probably am), but light hitting an object imparts some momentum to it? Would it then be logical to assume that an object that emits light also gets affected by the momentum of the departing photons in the opposite direction of the emitted light? Then if a body is facing the sun for an extended period (with almost no atmosphere), could the accumulated momentum of the light hitting the object and the light emanating from it (infra red) have at least some effect on its orbit?

Yes, but it's a known effect that can be calculated from known laws. The original post was about looking for unknown effects. Casimir Drag for instance.

Originally Posted by Twaaannnggg

Ohooooooo.....let's not even go down this road. I mean there's discussion about the diameter of Pluto (poor li'l thing got demoted from planet to planetoid already) let alone the exact position. This is not even known with enough accuracy to find small deviations for Mercury.

Replace mercury and pluto with your favorite two well-studied astronomical bodies of different temperature if it makes you happy - I was just going for a dramatic temperature example. Of course we don't have perfectly precise information on mercury or pluto, but we can track them well enough to know that they seem to obey the same fundamental orbital mechanics. If you want to say that this isn't a good "test case" because we can't measure them precisely enough, it raises the question of exactly how sensitive your equipment will need to be before you consider any other experiment acceptably accurate

> In the end, all of Physics is just a Theory. Would that than make it a
> one giant Assumption? By your reasoning; Perhaps. And so, as
> scientists, shall we spend our lives questioning all of the fundamental
> blocks that make up Physics? Or accept them to be relatively accurate > and move forward?

Yes we should continue to question the fundamental building blocks. This is exactly what people like Galileo and Einstein have done throughout history; they've observed that the facts didn't fit the theory and created new theory to explain the newly discovered facts, thus we have theories like General Relativity.

We have to realize that we know more facts now then scientists knew in the past. We may have learned a lot of those facts by testing those older theories, but that doesn't mean that those theories are absolutely correct, because the more facts that are used to create a theory, the more accurate that theory is. But no matter what, a theory is conjecture: "I believe this is the explanation for these observed facts." No matter how much fact supports a theory, a theory by definition is conjecture. And when we assume a theory is correct and use it to make another theory that seconday theory no matter how accurate it seems to be is still conjecture based on an assumption and thus is in itself an assumption "If we assume this theory is correct, then would can assume this other theory is also correct".

Newton didn't know about atoms, he had a theory that any type of matter was made up uniformly of the same component part which was uniformly distributed throughout that matter and if you had twice as much matter you had twice as much uniformily distributed component parts. This is what Netwon refered to as mass, which is NOT the same as atomic mass.

Netwon had no way of knowing the mass (under his definition) nor the atomic mass of the earth, nor the moon.

To Netwon the earth and the moon were each predominantly one type of matter evenly distributed throughout both. This was the model he used to create his original theory of gravity, in which he assumed that the attractive force of an object was relative to the amount of uniformally distributed parts of matter contained within the object. To Netwon gravity was proportional to the volume of the matter (notice I didn't say mass) and the pressure that volume of matter was under, thus an object could have more matter compressed into a smaller space, or vice versa increasing or decreasing it's gravity.

He then used the relative dimensions of the Earth and Moon to calculate the forces acting on one another and calculate their relative gravities, Based on this math he was able to somewhat accurately predict the oribit of the Moon, which he fine tuned using the variable of the pressure the matter of earth and the moon were each under.

When his math was applied to other objects in the solar system to predict their orbits based on their observed volume it didn't actually work.

To resolve this, instead of using an objects expected gravity based on volume to predict it's orbit. It's orbit was used to predict its gravity. This meant that gravity was not dependant on an objects volume as Newton had originally assumed. But the one assumption Newton made, that gravity was a static property of matter was kept, thus gravity became relative to atomic mass instead of volume. Flipping this equation partially led to the discovery of Neptune, because once we used the orbit to assume the fixed gravity of Uranus, we were able use the small variations in it's orbit to postulate that another object was influencing the orbit.

Then of course, more facts came to light and now we have General Relativity. Of course General Relativity is still only a theory, and should be tested and revised as is nescessary as new facts come to light just like any other theory. No matter how many trillions of dollars and careers have been vested on those "building blocks" being correct. Science is supposed to be about furthering understanding, not keeping the old boys from being challenged -- that's what politics is for.

After all how will we ever advance understanding if we make the assumption that all the previous assumptions that have been made by people who knew less than we know now were correct? In the future I would hope that hundreds of years from now science will be questioning the theories that we have created today, because if all goes well they should have significantly more facts avaiable to them then we have now.

Indeed, if the underlying theories are so sacred as to be unchangeable and challenging or testing those theories in new and creative ways is dismissed as unescessary, discouraged or even condemned, then that in fact would make science a religion.

So as it stands right now, no one has ever seen or heard of this version of the experiment being conducted.

Cheers,

Rai