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Re: car acceleration



If a ball is thrown against a horizontal spring, the spring compresses and
then extends. The ball is then sent back in the other direction. As the
spring constant k goes to infinity, the spring appears to act like a wall.
Does it? Does the physics change? Is energy stored in the k=infty spring
when it is compressed, even though the amount of compression is
infinitesimal?

____________________________________________
Robert Cohen; rcohen@po-box.esu.edu; http://www.esu.edu/~bbq
Physics, East Stroudsburg Univ, E. Stroudsburg, PA 18301

-----Original Message-----
From: John S. Denker [mailto:jsd@MONMOUTH.COM]
Sent: Wednesday, February 06, 2002 12:09 PM
To: PHYS-L@lists.nau.edu
Subject: Re: car acceleration


Rick Tarara wrote:
...
During the push
there MUST be some deformation of the wall.

Some deformation? Yes.
Significant deformation? No, not for realistic
walls and realistic hands.

That deformation may be very small,

yes.

but then the forces are very large.

No, the force is specified in the statement
of the problem. The amount of deformation is
given by the specified force divided by the
stiffness of the wall, and the divisor is
usually very large.

Energy is stored in the deformed
wall BUT came from the person.

Is there the slightest evidence that this
energy is significant? I haven't seen any.