Guys, let's check out this problem here. We're given some information about windmill blades. We're told that they spin at a rate of 20 revolutions per minute. And what we want to do is, at this rate, how long, which is really just a time, does it take for a windmill blade to complete one full rotation? So let's check this out. If you're ever unsure what variable that is, just go ahead and write it down.
How long a time is really has a unit of a second. So we're calculating the number of seconds to complete a full rotation. So that's number of seconds per number of cycles or rotations, whatever that have you. And remember that seconds per cycle is actually the period. So that's what we're trying to find here. What is the period if we have these blades spinning at 20 revolutions per minute?
So if you take a look at our equations, we know that there's a shortcut to calculate the period. You could just take one over the frequency. Remember that these things are basically just inverses of each other. All you have to do is flip the fraction. So what happens is we want to calculate the period and then we're going to have to calculate the frequency. So the frequency, remember, is just the opposite, the inverse fraction of that, which is really just the number of cycles divided by the number of seconds.
So if we take a look at our problem here, do we have cycles per second? And we actually don't. We actually have 20 revolutions per minute. So basically what happens is that whenever you're given revolutions per minute, which is an RPM, it's a pretty common unit that you'll see in these problems, all you have to do is just to get the frequency, you're just going to divide that RPM by 60. The revolutions per minutes, if you want it in revolutions per second, all you have to do is just divide by 60 seconds. Right? Because that's how many are in minutes.
So, really, what happens here is to get the frequency, we're going to do 20 RPMs, so this is RPM, divided by 60, and you're going to get 1 over 3. So that's basically 1 third, and remember the units for that are hertz. Now remember the reason we calculated this frequency is because once we get this as a fraction or whatever number it is, all we have to do is just take one over that number. So now we can figure out the period. The period is really just well, if we're taking 1 third, that's our hertz. Once you flip the fraction, it really just becomes 3 over 1, and that's just 3 seconds. And so, basically, it just takes 3 seconds for these blades to complete a full rotation. Alright? So that's really all there is to it. Let me know if you guys have any further questions.