On Thu, 03 Nov 2005 14:41:50 GMT, Ignoramus12686
wrote:

On Thu, 03 Nov 2005 14:24:15 GMT, Dave Lyon wrote:

"Ignoramus26745" wrote in message
...
On 2 Nov 2005 21:35:18 GMT, Dave Hinz wrote:
On Wed, 02 Nov 2005 21:27:03 GMT, Dave Lyon
wrote:

My understanding is that every action has an equal and opposite
reaction.
Therefore, the energy that is applied to the bullet must be absorbed by
the
gun and the shooter in the opposite direction.


Snipped the other Dave's comments


OK, today I am actually sober.

Let's not confuse energy with momentum.

Apparently I am (still).


Momentum is mass multiplied by speed. Energy is mass multiplied by
speed squared, divided by 2. Momentum is a vector and has direction
(the direction of movement), and energy is scalar, it is a single
value.

So, momentum is the same thing as acceleration?

No, it is not the same thing. Acceleration is tha rate of change of
speed of movement. Momentum is mas multiplied by speed of movement.

Unless the bullet weighs exacty as much as the gun,
there is no reason to expect energies of the gun and the bullet to be
the same.


This is where I get lost. If the acceleration of both items is proportional
to their weight, why wouldn't their energy be the same?

Acceleration (speed increase) is inversely proportional to the weight.

Energy is mass by speed squared. If one object's mass is 10 times the
mass of another object, that another (lighter) object would fly 10 times
faster than the heavy object. The energy of the lighter object would
be a result of 10 times greater speed, squared (100 times), divided by
the difference of mass, 10, so it would be 100/10 = 10 times greater
than the energy of heavy object.

I understand that
the larger item is moving slower, and the smaller one is faster. I don't
understand why their ability to do a given amount of work would be
different.

If I apply 1000 newtons of force to any size object to get it
moving, assuming we didn't loose anything to friction, won't we need
1000 newtons to make it stop? Doesn't that mean they have the same
energy?

No.

For example, you can accelerate a sledgehammer using, say, 100 newtons
of force. That would accelerate it relatively slowly.

Then the sledgehammer would hit concrete, stopping very quickly. That
could easily produce, say, 10,000 newtons of force, although acting
for much shorter time than it took you to accelerate the sledgehammer.

The time multiplied by force value, though, would be identical for you
accelerating the sledgehammer as well as for concrete stopping it. In
the above example, it would take concrete 100x less time to stop the
sledgehammer compared to the time it took you to accelerate it.

i

I like to use the analogy of the vault door.

With one finger pushing firmly, you can close a several thousand pound
vault door over a couple minutes.

Swing a 16lb sledge at the same door..and you may move it a few
inches, and have the sledge rebound nearly out of your hands.

Gunner


"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the **** out of you
for torturing the cat." Gunner