Changes

By Supergeek(http://www.airsoftretreat.com/reviews/showproduct.php?product=59&title=retreat-challenge-3a-physics-is-your-friend&cat=51)

Way back in the day, Aristotle thought that things move through space because of an inherent property of impetus. It wasn't until the enlightenment and the 17th century that the true nature of motion was conceived by Galileo and formulated by Newton. The most basic concept is this: things are moved by force - every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it (law 1). What is force? That's the second law - essentially '''f=ma ''' (force = mass * acceleration). This is the most basic equation in physics. Force is solely dependent on the mass of an object, and how much it is accelerating. Acceleration is change in velocity - it can be positive (going faster) or negative (going slower). Velocity itself has nothing to do with force.

Think about it this way - you're sitting in a car that's driving at 60 miles per hour. You don't feel anything, because the velocity is constant. But then, let's say that the car crashes into something. That's going from 60 to 0 in... let's say .1 seconds for simplicity. Converting 60 mph to meters/sec in metric (everything in physics is metric) and dividing by .1s, we get 268.2m2 m/s2s^2. That's the acceleration. Say you weigh 150 pounds. That's about 68 kilograms. That means that a force of over 18,000N is applied to you. That's quite a bit of force. So, in short - you feel it, whereas you don't feel anything when the car is just going steady.

So now that we know about force, we can talk about motion. Kinematics is the study of motion. We can simplify the path a BB takes by ignoring air resistance (which is a real pain to calculate) making two dimensional - we don't care about sideways motion. All we care about is the BB going forward and the BB going down to the ground. Another key principle - in this simplified two dimensional view, the two dimensions of motion are independent. What does this mean? It means that something will fall at the same speed no matter how fast it's going forward. Stand on a cliff over an ocean. Shoot a bullet perfectly straight over the water and drop a bullet at the same time the first bullet leaves the barrel. Negating the curvature of earth, any affects of rifling, and terminal velocity, both bullets will hit the ocean at the same time. So, while the first bullet is flying out at very high speed, it's also dropping at the same rate of acceleration that the second bullet is because of gravity. Near the earth, this acceleration is 9.81m81 m/s2s^2. Which means that every second, you're going 9.81m/s faster.