This video introduces pi, then it covers how to calculate circumference when you're given radius or diameter. It also covers those tricky problems where they give you circumference (sometimes it doesn't even have a pi in it) and expect you to solve for radius or diameter. Tricky stuff!

Basic Circuference, Pulley & Wheel Word Problems

This video covers word problems involving only one rotating part. Could be a crank that raises water up from a well. Could be figuring the distance or velocity of a wheel given a number of rotations. If you're in geometry you may need this video, but it's mostly for students in more advanced classes, either honors geometry or algebra 2.

Difficult Gear & Pulley Word Problems

This stuff is probably not in your geometry class, it's more for physics students or students in pre-cacl or trig who have really tough teachers, or for students interested in engineering type stuff. Gear ratios are explained as they pertain to bikes, cars, and we'll even learn how to tell how fast your bike is going from the pedal rotations!

Why Bikes & Cars Need Gears

This video definitely falls under the category of "only if you're interested in mechanical stuff", but it's important nonetheless because knowing how little stuff like bike gears work can be really important in other types of science and engineering, or even riding bikes.

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If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)