What's your basic understanding of gravity?

[packoman]

[CarewsEyebrowDesigner]

They aren't of the same size and shape

[mjmooney]

Of course, according to Zeno's paradox, neither object would ever hit the ground at all, it would merely get closer and closer to it, by ever decreasing distances.

[TheDon]

TheDon's wrong, though.

If I'm wrong then so is NASA.

Are you going to argue with NASA?

The bit you're wrong about is your explanation.

What you want is one of the most well known equations, f = ma, the force acting downwards on the heavier object is going to be higher than the lighter object due to the higher mass....The drag on both objects is going to be the same at the start....Each object will stop accelerating when the drag is equal to ma, which happens far faster for the lighter object.

In a vacuum, you said (rightly) that they will both hit the ground together.

In a vacuum drag =0. Taking the F=Ma equation you mention, your explanation implies that as the drag on both objects is the same (zero) and that the force on the object with the greater mass is greater, and that it will not stop accelerating and therefore will, because of the greater force have greater acceleration and therefore greater velocity....hit the ground first, but this is inconsistent with your assertion that they will both hit the ground together (in the vacuum).

I just think it's poorly explained. The acceleration for both will be identical at 9.8 m per second per second, the drag will be the same (zero) therefore their rate of change of position will be the same, and that's why they will hit together in the vacuum.

In the real world (paddy's desk) the downwards forces will be as per the vacuum scenario, the drag will be the same for each object, as they are the same size and shape, but for the object with more mass there will need to be more force from drag acting against it to stop it accelerating, so it's terminal velocity will be greater, though this will have negligeable affect unless the objects are dropped from a great height, as neither will reach terminal velocity before hitting the desk/floor.

I don't quite understand your issue with what I said.

I said in a vacuum they'll hit the ground together because there's no drag.

I'll go through what I said to explain it a bit better:

The drag on both objects is going to be the same at the start.

Each object will stop accelerating when the drag is equal to ma, which happens far faster for the lighter object.

Nice and simple, zero drag at the start (as they're at rest) and they'll stop accelerating when the drag counteracts the gravitational force.

The heavier object will also accelerate quicker, as as soon as they start moving the drag counteracts a larger portion of the force due to gravity on the lighter object.

When you release them drag starts building up straight away, counteracting the gravitational force. The drag is only the same at the moment of release, after that it's different (actually the larger object gains more drag, due to the fact it'd be moving faster)

Now due to the fact they have the same drag co-efficient at the moment in time immediately after release they both have the same aerodynamic drag acting on them counteracting gravity, but the same drag on both objects doesn't equal them slowing down the same, the lighter object slows down more as it's counteracting a larger proportion of the gravitational force. If one object is 10x denser than the other it will require 10x the drag to slow it down an equal amount.

This means that at any moment in time after release the acceleration of the larger object is going to be higher.

It's not just about terminal velocity, but right from the outset the smaller object slows down faster than the larger.

I don't think that explanation is wrong, just far too concise in that it doesn't explain itself well.

[TheDon]

I must commend TheDon on his use of 'retards' in his previous post. I had no idea it could be used in that context.

I had to put it in there, many a physics lesson was spent giggling like a fool at the teacher saying retards. I narrowly avoided detention for asking "so as you're sitting down at your desk, does that mean you're completely retarded?" after he introduced us to the concept.

[leemond2008]

nerds

[JulieB]

The heavier item because the force of gravity is always stronger on a heavier item in normal atmospheric conditions...

I'm presuming that's correct from memory of O level Physics... or am I having a blonde moment?!

[TheSufferingVilla]

There we go I just dropped a balloon full of water and a balloon exactly the same size and shape but filled with air out of my offices 20th story window onto 5th Avenue below. The big angry bloke who got hit square in the head by the water balloon was able to climb 20 flights of stairs and punch me in the face before the other balloon hit the ground somewhere across the river in New Jersey. True story, I swear.

:winkold:

[dont_do_it_doug.]

The heavier object.

I almost felt a bit of an idiot after reading the first few posts, until someone pointed out that the missing word "vacuum" is all important.

[ender4]

read the whole thread & now i'm confused.

whats the actual correct answer to the opening question?

[CarewsEyebrowDesigner]

There is no correct answer.

Everything is an illusion.

/thread.

[Wol.]

I went Heavier before reading on. The last time I read up on gravity I stopped when I got to Quantum Mechanics, and then decided it was all probably just Gods will holding us together.

[CVByrne]

The concept that gravity slows perception of time is very interesting. Also that every person experiences the passage of time differently is another interesting idea.

Though my actual practical knowledge of gravity only goes as far as big G and little g, Gravitational Constant and the Acceleration due to gravity on earth (9.8m/s^2).

I do know that the weight of an object is due to gravity, gravity gives weight to mass.