 In this video, I'm going to be talking about some alternative units for rotational motion. I'm assuming you already have seen my other videos on rotational motions, if not, the links to them should be somewhere below. Let's just quickly review, in rotational motion we're going to give the position as an angle in radians, the angular velocity in radians per second and the angular acceleration as radians per second squared. So basically our SI units are all based on radians. We also have the period, which is the time to go around a circle once, which is either the circumference 2 pi R divided by the linear speed V or the whole circle 2 pi in radians divided by the angular velocity. Now what are the alternatives? The main alternatives are the following. We could have one rotation, could say this is equal to well in radians, let's first look at the SI standard units, so as radians a full rotation is 2 pi radians. Alternatively, we could give it in degrees, you could say this is 360 degrees, or another rather popular unit is revolutions, so one revolution. This one is the SI, the other ones are the alternatives. Now just to make problems more complicated, often angular speeds are given in revolutions per minute, so what is an RPM? One RPM is equal to one revolution per minute. Now if you want to play it safe, you will convert this into the SI standard unit based on rads and seconds. So how do we do that? First I want to get rid of one revolution, so one revolution goes down here and I want to replace it with its equivalent in rads, so 2 pi rads. This way the revolutions are cancelled and replaced by radians. Now I do the same with minutes, you might remember that this is standard unit conversion that I showed you in a video at the very beginning of this series on mechanics. So minutes, I want to go to seconds, so I have minutes on top, I want to eliminate minutes, one minute is equal to 60 seconds. So in the end, if you need to go from RPM, revolutions per minute into rads per second, your SI standard units, you multiply this by 2 pi and you divide it by 60 and you will get rads per second.