I vaguely remember the concept of inertia from physics class in school, a long long time ago – where things that are in a state of motion stay in motion, and things that are at rest stay at rest until a force is applied… something to do with a body’s resistance to change, and friction and transference of energy and momentum. Oh, and I also remember that momentum equals mass times velocity – the heavier the object and the faster it is travelling, the greater the motion it has.
And I remember the fun we had as kids playing with a Newton’s cradle, a rigid frame with five metal balls hanging from it, suspended taut in a row like small swinging pendulums with only a left-to-right or right-to-left motion possible, where letting the first ball swing onto the next with a satisfying click would cause only the last ball to swing out at the opposite end while the three central balls stayed steady. Swinging two balls together would make the corresponding two at the other end of the row swing out with only the central ball staying still, and swinging three would make the central one move back and fore in almost in a state of perpetual motion.
I say almost because there is always a tiny loss of energy in each transference of energy between the balls (isn’t that where the friction bit comes in?) that eventually causes the movement slowly to reduce and then finally stop. Hmmm… I’ve maybe not remembered any of my physics lessons correctly, but I think I might have to apply some serious force in order to achieve the momentum needed to get myself going again to find mysef a new Newton’s Cradle to play with… 🙂