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Boomer likes to be cryptic.

It's his modus operandi.

"Freedom is never more than one generation away from extinction"

Ronald Reagan

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Boomer likes to be cryptic.

It's his modus operandi.

"Freedom is never more than one generation away from extinction"

Ronald Reagan
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Mexactly

The reason is "inertia".
"An object at rest tends to stay at rest, and an object in motion tends to stay in motion". When the feather and hammer are dropped the feather SHOULD accelerate faster and reach it's terminal velocity more quickly than the hammer due to the hammers greater inertia.

"We sleep safely in our beds because rough men stand ready in the night to visit violence on those who would harm us". George Orwell

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The reason is "inertia".
"An object at rest tends to stay at rest, and an object in motion tends to stay in motion". When the feather and hammer are dropped the feather SHOULD accelerate faster and reach it's terminal velocity more quickly than the hammer due to the hammers greater inertia.
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As much as you think it SHOULD, it doesn't happen like that <img src=icon_smile.gif border=0 align=middle>

Why?

Because gravitational and inertial mass, m_g and m_i respectively, have the same value. Gravitational mass is measure of the strength of an object's interaction with gravity. Inertial mass is a measure of an ojbect's inertia (resistance to change in motion). From the law of gravity and newton's 2nd law we see for an object in a gravitational field:

m_i*a = m_g*g,
m_i and m_g are equal therefore a = g.
Therefore, the acceleration for any object, regardless of mass, is gonna be the gravitational acceleration. Feather and hammer will reach the ground at the same time, if dropped from the same height.

So compactly, all objects in the same gravitational field fall at the same rate if and only if the ratio of gravitational and inertial mass is always the same. All experiment's have found this to be the case. Einstein's General Theory of Relativity depends on this also.

2nd point. There is no such thing as terminal velocity in vacuum. Terminal velocity happens on earth because of drag. Now the moon, for most practical purposes, has no atmosphere. Hence is pretty close to a vacuum, so the astronauts didn't see anything reaching terminal velocity there.



Edited by - feynman on Aug 16 2004 5:35 PM

Just thought I'd add a simplified version to what I'm saying above.

You are right that the hammer has more inertia then the feather, which means it will be harder to accelerate. However, the hammer experiences a larger force from the gravity than the feather (because gravity "pulls" stronger on more massive things), and this is what counter acts the fact it has more inertia, and why they both end up having the same acceleration.

Details are in the above post though.

Ah, but the hammer WOULD take longer to deccelerate!



"Freedom is never more than one generation away from extinction"

Ronald Reagan

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Ah, but the hammer WOULD take longer to deccelerate!


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That all depends on various details <img src=icon_smile.gif border=0 align=middle> But ya I can think of some circumstances where it would take longer to deccelerate. I could think of some instances where it would take the feather longer to deccelerate also though.

Are you trying to be cryptic like boomer? <img src=icon_smile_wink.gif border=0 align=middle>

Ok maybe I was being a little cryptic in my statement too

So since my pizza has a little longer to cook, I'll be more specific.
the rate of decelerration of an object (meaning accelerating in the opposite direction of motion, or as commonly thought of..."slowing down") is totally dependent on the forces applied to the object, and the mass of the object.

So, with a given force, say 10 Newtons or something, if you apply that force opposite how the hammer is falling, and also apply it in the same way to the feather, than yes, the hammer will deccelerate slower.

However you could just as easily make them deccelerate at the same rate, or make the feather deccelerate slower. See how?

It's all in newtons 2nd law, F = ma. or put in another form

a = F/m. If you make the ratio F/m the same for both objects, they will decellerate at the same rate. You can make the feather deccelerate slower by making sure the following inequality holds:

F_feather/m_feather < F_hammer/m_hammer

Yes, but left to their own devices(in this case gravity and air density), the hammer would take longer to deccelerate, yes?



"Freedom is never more than one generation away from extinction"

Ronald Reagan

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Yes, but left to their own devices(in this case gravity and air density), the hammer would take longer to deccelerate, yes?
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Ahhh, are we out of the vacuum? Ok. Yes I would agree that statement.

I don't live in a vacuum, so i'm not particularly concerned with how fast things 'fall' in one, lol.

"Freedom is never more than one generation away from extinction"

Ronald Reagan

lol. True. True. But trying to understand the real world in all its compexity all at once is very hard So you break it into smaller parts and simpler cases. Getting rid certain things so you can focus on underlying concepts is very helpful. Then you can add in the air resistance and whatever later once you have a good understanding of whats going on. I'm sure you see this. I'm just pointing out why I was talking about vacuum, etc, just so we could focus on main points without being distracted by other complications.