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We learn in beginner science classes that all objects fall to the ground with the same acceleration; i.e. discounting air resistance, 2 objects with different masses, if dropped simultaneously from the same height, will hit the ground at the same time. But wouldn’t the heavier object also pull at the earth with greater force than the lighter object? If so, doesn’t the heavier object land slightly earlier?
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If I understand correctly, when visible light hits a solid opaque object, some of it is absorbed and some is reflected. This is what gives us colors. The absorbed light is now trapped in the object, correct? Does this make the object slightly more massive?
For 2, mostly the absorbed colors of light heats up the object. So it becomes hotter rather than more massive. Touching the top side of a dark car after it has sat in a parking lot on a sunny summer day will easily prove this.
For (1), sure the Earth accelerates towards the more massive object, but, since the two are dropped side-by-side, they still land at the same time. But, just like all of Physics 101, the thought experiment is simplified and approximated - the Earth is assumed to be fixed in space, have a uniform gravitational field normal to it’s surface, the balls are dropped in a vacuum, etc.
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Considering both masses to be point masses and classical mechanics, both hit the earth’s surface at the same time. You can consider the larger mass to be made by joining a lot of smaller masses.
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Yes. Anytime the temperature of a body goes up, the resulting energy increase also increases the body’s mass by E=mc2
The short answer to both of your questions is “yes, but to such a negligibly small degree that you’d never detect it”.
The first was the topic of an old, old thread, the very one which convinced me to be active on this board (though not quite the first I participated in). There are a lot of subtleties to it, though, and you can be sure that Dopers found them.
On the second, I wouldn’t say that the light is trapped in the object, since that suggests that it’s still light. The energy is trapped, but it’s converted to thermal energy. But yes, that increase in energy does mean a (very slight) increase in the object’s mass.
Thanks everyone.
Side question: Is it the photons from the light that create the thermal energy? If so, why wouldn’t it be accurate to say that light is trapped?
Create the thermal energy, no.
Converted to. Which is why it’s not accurate to say the light is trapped , it’s not light anymore, nor is it trapped. It is radiated as heat (assuming the object has already established thermal balance with it’s surroundings before the light hits it)
I guess in a way you could say it if the object is colder than it’s surroundings since then some of the converted energy is stored in the objects mass, but again it’s not (visible) light anymore.
Saying it’s trapped implies it could be released and re-emitted. While the energy could be eventually re-emitted, it won’t be as the same wavelength light. Instead it’ll be at a much longer wavelength, one deep in the infrared. But it won’t have to be re-emitted. The object is warmer because of the light, but it could cool down via conduction or convection.
So I’d say calling it “trapped” is not a very good way to describe the situation.
Because after it’s been absorbed and converted into thermal energy, it’s no longer a photon.
You can get very nit picky. The vibrational energy of the warmed mass is composed of a continual exchange of kinetic energy and potential energy in the form of repulsive forces between the atoms. Those repulsive forces are in part mediated by photons, and there will be more energy in them. No longer a single photon, but not fully dead yet.