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Offline TomInAustin

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UA and freefall speeds
« on: October 12, 2018, 03:09:46 PM »
This was discussed in an unrelated thread and I feel it's worth asking again.  How does UA account for objects of differing mass falling at different speeds?  Assuming that the air is either being accelerated or being pushed upwards by the ground then freefall speed based on drag is easy to grasp.  But the fact that an object with equal drag but more mass will fall faster is not easy to understand in UA.

An example, in skydiving there is a training aid called a space ball.  It's a tennis ball with lead shot in it and usually has some ribbon streamers as well.  The speed is governed by the weight of the lead shot.   

Thoughts?

Som beautiful shots




Do you have a citation for this sweeping generalisation?

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Offline Pete Svarrior

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Re: UA and freefall speeds
« Reply #1 on: October 12, 2018, 03:17:02 PM »
But the fact that an object with equal drag but more mass will fall faster is not easy to understand in UA.
How so? If the drag is equal, so is the force accelerating the object upwards. An equal force applied to two different masses means that the heavier item accelerates upwards at a lower rate. Thus, relative to the Earth, it's downward acceleration is faster.

Don't forget the Equivalence Principle. By the very rules that govern the RE model, UA must be locally indistinguishable from RET+gravity. If you somehow showed this to be false, you'd be disproving Special Relativity.
Read the FAQ before asking your question - chances are we already addressed it.
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P.S.  All of us illiterate folks understood this the first time.

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Offline TomInAustin

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Re: UA and freefall speeds
« Reply #2 on: October 12, 2018, 03:27:40 PM »
But the fact that an object with equal drag but more mass will fall faster is not easy to understand in UA.
How so? If the drag is equal, so is the force accelerating the object upwards. An equal force applied to two different masses means that the heavier item accelerates upwards at a lower rate. Thus, relative to the Earth, it's downward acceleration is faster.

Don't forget the Equivalence Principle. By the very rules that govern the RE model, UA must be locally indistinguishable from RET+gravity. If you somehow showed this to be false, you'd be disproving Special Relativity.

If I am getting what you mean, all objects are subject to UA based on mass?  Or are you talking about the drag?
Do you have a citation for this sweeping generalisation?