"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?



Newton's law states that the action (FORCE) is equal (but in opposite
direction) to opposing action (force). Note also that acceleration is
proportional to force (another newton's law, a = F/m). From here, you
would quickly see that any interaction between two bodies changes
their momentums by the same amount, only of the opposite direction.

I understand this part.



The law of conservation of energy is a fully different law. It means
that energy cannot be created from nowhere. It keeps oil prices
high.

Yep, I get this part.

In the case of shooting guns, the energy of bullets is given to
them by the burning gunpowder. Once the bullet flies out, gunpowder is
spent and burned.

Yep, still with ya.

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? 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?