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Kinetic Energy

Teacher/Instructor Matt Jones
Matt Jones

M.Ed., George Washington University
Dept. chair at a high school

Matt is currently the department chair at a high school in San Francisco. In his spare time, Matt enjoys spending time outdoors with his wife and two kids.

The energy of an object in motion is called kinetic energy. Kinetic energy is defined as the energy needed for an object to accelerate from a resting position to its current velocity. To calculate kinetic energy, we use the formula kinetic energy = 1/2 mass x velocity^2.

Kinetic energy is the energy of motion, so any moving objects have kinetic energy okay so kinetic energy the formula we use for kinetic energy is one half times the mass of the object time the velocity of the object squared. Okay, so if you can remember one half mv squared that is the kinetic energy an object has at anytime. If the object is not moving 0 kinetic energy, if the object has a mass of 0, 0 kinetic energy, okay so let's look at a couple of problems that you might be asked to solve involving kinetic energy. Okay first off, what is the kinetic energy of a 5 kilogram bowling ball moving at 2 meters per second? Okay so again the formula for kinetic energy is one half mass times velocity squared okay and in this case we're solving for kinetic energy so we just say one half times 5 kilograms times in this case 2 meters per second squared. Okay so to solve for that 2 squared is 4 meters squared per second squared times 5 kilograms equals 20 and one half of that equals 10 and remember energy units are always in joules. So 10 joules of energy in that bowling ball okay?

Let's look at another problem, let's say we have a 4 kilograms bowling ball and it has 20 joules of kinetic energy what's its velocity? Okay so this looks similar right but we've changed the mass a little bit and we can still solve it with the same formula, alright so let's say kinetic energy equals one half and mv squared okay this time what do we have? We have the kinetic energy right there 20 joules and it's going to equal one half times our mass 4 kilograms but we don't know our velocity squared, that's what we're solving for in this problem okay? So once we set that up again pretty straight forward problem to solve so I've got 20 joules equals 2 one half times 4 is 2 kilograms velocity squared okay. And now I want to divide by 2 and I'm going to get 10 joules equals my velocity squared so this is going to be just over 3, 3.1 so my velocity equals 3.1 meters per second alright. So again 2 different ways to use this idea of kinetic energy, number 1 given the amount of energy what's the velocity, we could also solve for the mass or we could just take the mass and the velocity and calculate the amount of kinetic energy in an object. As long as that object is moving it has got kinetic energy.