Monday, March 19, 2007

Force

A force is a push or pull on an object. It can be what you use to push a box across the floor, the gravity that pulls things down when they fall, or what keeps a maglev train floating above the track. An object can either use force directly like you do when you push the box, or as a field force like gravity and magnets. The difference is that the object that’s pushing has to touch the object that’s being pushed, but the field force acts from a distance. You’re probably expecting a formula, well here it is:


F=ma


…And here’s what it means: To find the force acting on an object, you multiply the mass of the object times its acceleration. That means force has a magnitude (size) and a direction.

Yes, there’s a special unit for force, too. If you multiply the units for mass and acceleration, you get Kg•m/s2 and


1Kg•m/s2=1N


If you have a 1 kilogram object and it’s accelerating at 1m/s2, a force of 1 Newton is acting on it.

But there’s always more than one force acting on an object. Say you were making a 1 Kg weight accelerate upward at 1m/s2. Here’s a helpful number:


9.81m/s2


That’s gravitational acceleration near sea level on Earth. The Earth’s gravity is pulling every kilogram down with a force of 9.81N. You’re actually pushing the weight up with a force of 10.81N. Both those forces together make a net force of 1N upward, so the 1 Kg weight can accelerate up at 1m/s2.


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