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Power 8,197 views

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.

Power is the rate at which work is done. It is related to energy, which is the quantity used to measure work. Power can be calculated by the ratio power = work / time and is usually measured in Watts (1 Watt = 1 Joule/second).

You probably know what power is and when we study Physics when we talk about power we're talking about work done over time. So remember the unit for work is joules, the unit for time is second, so now we have power and the unit we use for power is watts name for James Watt the guy that invented the locomotive engine a lot of power in a steam engine okay, so unit is watts and often when we're generating power, we're generating lots of power and in like a power plant of something. So we have some units that are quite common and one of them is if we have a thousand watts okay and to simplify that we can just call that a kilowatt okay or sometimes we just abbreviate that little k big W. But let's say we're generating even much more power than that well if we have maybe not a thousand but let's go to the next unit which is a million which also equals 10 to the 6 or a 1 with 6 zeros behind it okay.

Well the unit we use for that much power is a megawatt and sometimes we'll abbreviate that big M, big W. So these are all units for power, megawatts, kilowatts or just the regular watt okay. Let's look at some examples that you might be asked to solve involving power and its relationship to work time okay? Let's say for example you're pedaling your bicycle and you want to know how much power is required to exert 100 joules of work on a bike pedale for 5 seconds okay. So the formula again power equals work over time so this is a pretty straight forward problem we're going to, our work is 100 joules, our time is 5 seconds or I'm just going to abbreviate that s okay and so our power here 100 divided by 5 is going to equal 20, in this case 20 watts. So 20 watts of power is required to exert that force, I'm sorry that work on the pedal for that number of seconds.

Let's look at another example of where you're given a unit of power and you need to figure out how much work is involved in that. Again, so let's say how much work is required to power a 40 watt light bulb for 1 minute? Okay, so here we're given the power unit 40 watts okay but I want to know how much work is required to power it for 1 minute. Now remember here the unit is minutes and the unit we talked about for power is work per second okay. So let's remember that this is actually 60 seconds alright. And then we just have to setup our problem. We've got 40 watts equals the work x over seconds which is 60 seconds okay and again to solve for x I'm going to say x equals this number times this number, the number in the denominator times this number which is going to equal 240. And in this case the unit is watts I'm sorry watts times seconds is going to give us our number in joules. And so these are 2 types of equations that you'd typically be asked to solve involving power and its relationship to work.