the moon doesn't crash into the earth because there is no gravity in space
The net force on the moon, which supplies its centripetal force, can be approximated by the gravitational force by the Earth on the moon. This force is directed towards the centre of the Earth, which is also the centre of the moon's orbit. Thus, the moon is in uniform centripetal motion around the Earth.
I'm going to be incredibly pedantic about this one: (don't take this personally; university makes people pedantic because you lose marks otherwise)
The moon doesn't crash into the Earth not just because the centripetal force is supplied by the Earth, BUT also because the moon's perihelion (closest point to Earth) is more than one Moon radius away from the surface of the Earth. This sounds like a trivial point, but for obvious reasons, if the moon came too close to the Earth, then the Earth's gravitational force would no longer stop the Moon from hitting the Earth. Indeed, gravity would then accelerate the Moon towards the Earth and actually increases the explosiveness of any collision.
Also, just because the force is directed radially inwards, does NOT mean there is uniform circular motion. There is a direction AND a force requirement; if the force magnitude isn't right, the Moon's distance from the Earth will change.
If I unplug an extension cord quickly from a powerpoint and plug it into itself it'll store electricity forever The extension cord doesn't store energy. It just transmits energy; the energy comes from the wall, so if you unplug it from the energy source, you're not getting any electricity.
In circular motion, an object is pushed away from the center of a circle It may feel like it, but in circular motion, objects are pulled towards the center of the circle. Imagine you're travelling in a car about to turn in a clockwise circle, and you're currently at the 9 o'clock position. You're going up, but you're being pulled to the right to move clockwise. Where does the feeling of a force going to the left come from?
Well, as the car turns, you don't turn immediately. Newton's first law says that before any force acts on you, you still want to move up. Yet the car turns right. Therefore, from your perspective, you're moving to the left inside the car and get squished against the left door of the car. Normally, when doors push on us, we interpret this as being pushed onto the door, so being squished against the left door of the car feels like something from the right is pushing you into the door. Except, of course, nothing is actually pushing you.
Here are some of mine:
If you're on a plane, you can put a wind-turbine on the plane to get free energy from the relative motion of the air against the plane. If you jump out of a plane, you're going to be flung backwards really quickly because you're no longer flying on the plane. If you hear two balls hitting each other, the lost energy is mostly attributed to sound and heat. (I am referring to one of these not being important) You get heavier as you move faster. This is a pet peeve of mine.