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Re: car acceleration



At 11:06 06 02 2002 , you wrote:
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?

Why do we make things so difficult? Say it correctly and things make sense:

Someone/thing does _work_ on a ball and thereby increases the ball's
property of energy.

The ball strikes a malleable object of some sort (spring, soft wall or
whatever)

The ball does _work_ on the object and thereby increases the property of
energy of the object and in addition decreases the property of energy of
the ball. Delta total E=0.

If the ball strikes a non-malleable object then the Earth (or maybe the
entire Solar System) moves -- well, the Earth moves in any case -
but.... The property of energy of he Earth increases and the property of
energy of the ball decreases The delta total energy =0

Now this language is awkward and may not be needed, but if the associated
mental process is not followed, we get into some pretty silly discussions.

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen