Unrealistic Biome after Planetoid impact ...

What`s a KEW?

Kinetic energy weapon.

Something with mass travelling at speed.

Think about a ball bearing travelling at 90% of the speed of light.

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The answer was already covered pretty well, but basically you're confusing Newton's laws with the conservation of energy, and misapplying the principal of the conservation of momentum.

Conservation of momentum assumes that the system is closed.

No. And ignore Timberwolf, he is incorrect.

When you start accelerating the car, you apply a force to the surface of the moon. Specifically, you apply a force to a particular set of atoms.

They apply the same force on your car. That causes your car to accelerate forwards. Your car gains velocity. It therefore gains momentum.

Conservation of Momentum does not apply. You had an initially stationary car which transformed chemical potential energy into kinetic energy. The car still has the same amount of energy, but now there is more kinetic energy and less chemical potential..

There is friction between your atoms and their neighbours. That friction causes energy to be lost as heat. Each neighbouring atom therefore receives less force than the original atoms you applied a force to.

With friction - to start something moving you have to apply more force than the frictional force. You know that. It's how glue works. Glue increases the "friction" between two surfaces. Otherwise, slip occurs, and the particle moves

Assume you are accelerating to the left. The first particle you applied force to is on your immediate right.

By the time the force has travelled around the entire moon to the particle on your immediate left, all the energy will have dissipated as heat through friction, and the force applied to it will be smaller than the friction required to achieve slip. It will not move.

There is no application of rotational momentum. The moon isn't rotating. There is an application of force.

When you brake, you remove the force that your car applies to the surface of the moon (in the "forwards" direction). The frictional force remains unchanged. You also increase the friction between the wheels and the brake pads. You decelerate. The car loses momentum. The total energy of the system remains unchanged - you have transformed your kinetic energy into heat.

If you tap a tuning fork in space, ignore Timberwolf's explanation. Graphene has a perfect lattice structure. The more correct explanation is that over time, your Graphene tuning fork will transform its kinetic energy into heat through radiation.

Yes, eventually. I'm kind of now disagreeing with the above explanation.

Think about a train. If you shove a train carriage, you don't move the train carriage. Your shove wasn't enough to overcome the friction force opposing the trains motion.

If you get a couple of hundred people to shove the train, it moves. The force was larger than the friction force.

The thing that is important about kinetic energy is that it depends on your frame of reference. When you say that something is at rest you have determined this to be your frame of reference.
If you have 2 cars traveling at the same speed in the same direction there is no kinetic energy that can be traded between them. In order for the cars to be able to build up kinetic energy to each other you need to accelerate the cars to different speeds and this can be done by either braking one of the cars or pushing the gas on one of them. In either case the car will trade kinetic energy with the ground to build up kinetic energy to the other car.
Newtons Third law of motion: "When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body."
There is a very real trade of momentum between the ground and car and it will spin the planet. It doesn't matter if the car have the same mass as the planet or if the car is much lighter.
Even light carry momentum.
http://en.wikipedia.org/wiki/Beam-powered_propulsion#Direct_impulse
When you start a laser pointer it exerts a very small force in the opposite direction of the laser beam.
Radiating heat is light so heat also carries momentum.

In a non-classical sense, kinetic energy is never lost, it just transferred to another object or wave.
You could say that heat leaves the system without applying any force when it radiates from the system uniformly. If I understand this correctly it means that whenever 2 objects trade kinetic energy and the excess energy leaves the system uniformly the 2 objects always have an even trade of kinetic energy.

I'm not sure how this is relevant to the discussion. Pushing a train carriage before it moves is basically like loading a spring. You load the spring and build up potential energy. Once the force from the spring is large enough to overcome the friction from the carriage the potential energy will be transformed into kinetic energy and the carriage will start to move.

.. Oh sod it.

@maxpowerz ; @menchfrest - Engineers, Unite!

Well. I just learned more reading these 2 pages of forum posts then I did in school.