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Posted by MEC (Member # 2968) on :
 
I was wondering about instantanious changes today and I had a thought. when an object at a high velocity hits a stationary object, and the stationary object is emmbedded in the moving object. does the stationary object's velocity increase instantaneasly?
 

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Posted by T. Analog Kid (Member # 381) on :
 
no...

the distance over which the acceleration happens is the distance it sinks into the moving object. Once you know the distance and Vf (Vi=0, right?) you should be able to calculate the (very small) time.

edit to add: this works for all collisions, too, in real life, where there is *no* such thing as a perfectly elastic collision. The distance is given by the amount deformity druing the collision, or , alternately, you can just measure the time that the two objects are stuck together...

[ March 22, 2004, 09:57 AM: Message edited by: T. Analog Kid ]
 

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Posted by MEC (Member # 2968) on :
 
That's what I thought.
 

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Posted by Hobbes (Member # 433) on :
 
It's an interesting question because common sense says that at some point, the object velocity must increase from zero to another number. Seeing as how at time t = 0 the velocity is 0, and at some future time t = n the velocity is equal to a very high number (assuming relativley in scale masses). However, conventional physics (Newton and on) says that actually there are an infinite number of instants of time between time t = 0 and t = n, no matter how small n is. So you can create a range in which the velocity changes, but the word "instantly" becomes impossible to define since there is no instentanous "now" that exists in the current world of physics.

Hobbes
 

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Posted by mr_porteiro_head (Member # 4644) on :
 
At least, not without an infinte force.

But once you get those, what happens if the terrorists get one too?
 

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Posted by Bob the Lawyer (Member # 3278) on :
 
You could sink lots of money into a Global Infinte Force Defense system.
 

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Posted by T. Analog Kid (Member # 381) on :
 
Unless you are in a Classical Mechanics class with a sadistic instructor, you are much more likely to be given a Force and asked to solve this by Momentum and Impulse.
 

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Posted by T. Analog Kid (Member # 381) on :
 
Hobbes, I have a friend that is very into the idea that time and space *are*, in fact, in individual units and that the universe is *not* a continuous line, but a number of discrete points so close together that they appear continuous. The idea is that this is the reason for the heisenberg uncertainty priniciple: that we can only measure down to a certain point because nothing smaller exists. He has, much to my chagrin, largely built his life around this theory.
 

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Posted by Hobbes (Member # 433) on :
 
Is that person me? Seriouly though, I'm a big believer in the discrete universe theory, in fact, I wrote a Cousin Hobbes on it once... I'm not sure I really want to dig it up because it was rather poor writting as I recall, but if you want to search for it be my guest.

Hobbes
 

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Posted by T. Analog Kid (Member # 381) on :
 
I think I remember that, now... yeah...

He just thinks that Discrete Universe implies a perfectly material one as well... he is a natural determinist based on that and I have seen him make some damned poor decisions because he doesn't feel like he has any choice in the matter. It's a terrible thing to watch a friend abdicate their will.
 

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Posted by mr_porteiro_head (Member # 4644) on :
 
When I was at school taking a beginning engineering class, the professor was at the board going through a problem. "So you have a massless rope and two massless, frictionless pulleys...", just the same as we had done dozens of times.

He suddenly stopped, turned around and said "Massless and frictionless pulleys are a little expensive, but here at the University we believe that your education is worth it."

We were kinda stunned because he was not the type to crack jokes. I think that getting married again (he had been a widower for a *long* time) helped him loosen up a bit.
 

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Posted by rivka (Member # 4859) on :
 

quote:

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"Massless and frictionless pulleys are a little expensive, but here at the University we believe that your education is worth it."

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I am so going to use that line!

quote:

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I think that getting married again (he had been a widower for a *long* time) helped him loosen up a bit.

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