04-05-2002 20:36									#121
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Cool, if somewhat destructive. It looks like they should form a bigger single galaxy afterwards!

	04-05-2002 20:47									#122
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Not as destructive as you might think.

It looks vicious but that time sequence was sped up from 1/2 billion years to 16 seconds (of action)

	05-05-2002 04:10									#123
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Here is my latest trivial question:


What do they mean by a four-head VCR??

	05-05-2002 04:57									#124
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I would guess that that's the number of read/write magnetic heads the VCR uses...

	05-05-2002 05:06									#125
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Is it true that a fly flying inside a car doesn't get squished to the windows because the car's velocity isn't (over) 1 g? (or was it capital G) If not, then what is the reason?

	05-05-2002 05:07									#126
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The quick answer is that you're talking bollocks.

	05-05-2002 05:08									#127
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Especially neither g nor G are measured in the same units as velocity...

	05-05-2002 05:09									#128
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quote: Originally posted by Sandman Why are dodgy medical doctors called 'quacks'?

"Quack" is a short form of the now obsolete "Quacksalver", from C16th Dutch "quack salf", meaning "To Hawk Ointments". Which is what a Quack does, really.

	05-05-2002 05:12									#129
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I thought of this problem once when I was driving into Salt Lake City. I saw a sign that said "SLC 70 miles" and I was going 70 mph so I figured I would be there in an hour. About 55 miles out of town I saw a sign that said "SLC 55 miles" and a speed limit sign that said "slow to 55 mph". Later when I was about 30 miles out of town the speed limit sign said "30 mph". So I had apparently travelled all of that way for nothing because I was still an hour away from town.

My question is, should I break the speed limit or spend the rest of my life traveling to Salt Lake City?

	05-05-2002 05:13									#130
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Depends on the placement of the signs...

	05-05-2002 05:16									#131
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Okay, I new I was probably skating on thin ice there. But then what the hell is it that keeps the fly from facing a horrible death splattered all over the back window?

	05-05-2002 05:19									#132
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You mean when the car is accelerating?

His ability to flap his wings fast enough to keep up to the increased "gravity" experienced inside the car.

	05-05-2002 05:22									#133
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Increased gravity? As in the pull towards the back of the car? This is starting to make sense, gradually.
But the pull disappears when the car's speed remains constant?

	05-05-2002 05:26									#134
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You've got it. To maintain position in an accelerated frame of reference, the fly has to provide both upwards lift to counteract gravity and forward lift to keep up with the car. Total acceleration needed is the vector sum of g (direction downwards) and acceleration (directed whatever way the car's accelerating).

In a steady-velocity car, the fly feels like it's standing still, since it's in an inertial frame. Note that it's important the car's enclosed, since otherwise the fly also has to deal with a 100 kilometer-an-hour headwind...

	05-05-2002 05:31									#135
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Does that hold true even if the car does not contain a vacuum? Surely air effects will reduce the force the fly needs to remain stationary.

	05-05-2002 05:31									#136
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All right... so the fly can keep it's life as long as the pull isn't so strong that it can't resist it. I figured it had something to do with inertia too... Case closed?

	05-05-2002 05:36									#137
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quote: Originally posted by Chowlett Does that hold true even if the car does not contain a vacuum? Surely air effects will reduce the force the fly needs to remain stationary.

Only in terms of its buoyancy (negligible, and ratio of this to total force does not change with acceleration, unless acceleration is sufficient to create pressure gradient). Force exerted due to air resistance is directly proportional to square of the speed of the fly wrt the air, so if it is to remain stationary then this can be ignored.

	05-05-2002 05:38									#138
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fair enough.

	05-05-2002 05:45									#139
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quote: Originally posted by KrazyHorse Depends on the placement of the signs...

More formally, if Salt Lake City is a limit point of the signs, then yes, it will take forever to get there.

It's frightening what a little analysis does to you...

	05-05-2002 05:48									#140
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However, given most road authorities can't make signs arbitarily thin or place them arbitrarily close together, you will eventually reach SLC unless they impose a speed limit of 0 or less.