Imagine 2 objects, 1 is a 50kg dumbbell and 1 is a 1g feather, how is it possible that they will fall and touch the ground at the same speed and time assuming they are dropped from the same height?
I must be understanding this completely wrong.
Edit: I definitely understood it completely wrong because I did not know it only applied to objects in space. That makes much more sense.
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First of all, this is only in a vacuum, where air resistance does not exist. Typically it still doesn’t matter *too much*, but with the example of a feather, it definitely matters.
The reason everything accelerates equally, is because for every “extra pull” they get from gravity (for being more massive), they have an equal “extra resistance to acceleration”, which we call inertia.
Gravity pulls *on mass*. Something twice as heavy is pulled twice as hard, but is also twice as hard to move.
These two effects cancel perfectly, however other things like air getting in the way may unbalance the rates and cause one to fall faster.
This phenomenon only occurs in a space completely devoid of air. When released in a vacuum with no air resistance they will fall at the same rate because gravity acts on the two bodies uniformly no matter the weight difference. The reason this cannot occur in an open air environment is because the force of the air resistance on the feather from all direction is enough to counteract gravity. The bowling ball, on the other hand, with a higher weight class can now through the air resistance forces.
It’s possible because acceleration due to gravity close to Earth is mass independent. This can be derived from Newton’s laws, basically the extra force necessary to accelerate a heavy object is exactly cancelled out by the fact that gravity pulls harder on heavier objects.
But your intuition isn’t wrong in the example you gave. A feather will not always hit the ground at the same time as the weight. But it’s not because gravity is working differently on them, it’s because there is *air resistance* that significantly slows down the feather, but doesn’t really affect the dumbbell.
I’m likely wrong on this, so someone please correct me, but:
Gravity isn’t a force and isn’t pulling. They are traveling straight through time and space. If those objects were floating in space, would you expect them to orbit differently given same starting variables?
One way to imagine why they can’t fall at different speeds is to imagine a small thing tied to a big thing. The small thing would fall slower and hold back the big thing that wants to fall faster, but also a small thing tied to a big thing is an even bigger thing that should fall even faster. The only way the whole thing works is if the small thing falls at the same speed as the big thing and the even bigger thing
I think a good way to reason about it is by thinking about what you consider an object. If you have two rocks and drop them next to each other they should fall at the same speed. If you tape a string to both of them so they’re connected, are the two rocks just one big heavier object now that should fall faster? What happens if you glue them together? The only reasonable conclusion is that gravity doesn’t care how much mass there is and everything takes the same amount of time to reach the ground. Unfortunately there is air everywhere that slows things down that move through it. That’s why a feather falls a lot slower than a rock. There is a lot more air that’s in the way compared to how heavy it is. That’s also why a crumpled up piece of paper usually reaches the ground faster than a sheet
To say that it only applies to objects in space (or more generally in a vacuum) is a bit of an exaggeration. Yes, air resistance is an important factor on Earth and not in space. But a feather is an extreme example of an object that has a very large cross section and low mass, and so it is greatly affected by air resistance. For many other pairs of objects, you’ll find that they do fall in almost exactly the same time when dropped from the same height, even on Earth, because there is almost no difference in air resistance. Take two coins of different weights, for instance, or take your 50-kg dumbbell and a 10-kg one, or a sofa and a table, or a tennis ball and a marble. If you drop them from a few meters, the difference in fall time will be negligible. It’s mainly when you consider very light objects (esp. things that have low density, i.e. are light relative to their size, and present a large cross section when falling) that you see any difference, but other than that, in many real-life situations you’ll find that you often can’t really tell if one thing falls faster than another.
> I definitely understood it completely wrong because I did not know it only applied to objects in space. That makes much more sense.
It’s still partially true here on Earth. It was discovered first on Earth after all. In situations where air resistance is negligible (the objects are heavy enough and the drop is short enough), objects will essentially fall at the same speed.
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