Uniform Circular Motion (a=v2/r)

The videos below cover the most basic circular motion problems, the ones you get BEFORE your class does forces, Newton's Laws, etc. In the videos below, we're just covering basic centripetal (and centrifugal) acceleration problems, including situations like satellites orbiting a planet, or a roller coaster going over the top of a hill. A later chapter of videos in the Forces section will cover advanced circular motion and F=ma problems.

Centripetal vs Centrifugal (Fictitious) Forces

This video explains the basics of the centripetal acceleration formula (a=v2/r), then it gets into explaining the difference between centripetal and centrifugal forces, also explaining why the latter are referred to as "fictional forces". Cool example: when you're in a car going around a turn, squishing the person next to you, are you squishing him, or is he squishing you?

Tangential vs Radial Acceleration

While most physics classes at least mention this topic, most don't dwell on it too much. The main thing is that you'll want to know what the terms "radial" and "tangential" mean, because those labels are often used in a wide variety of word problems, from rotating bodies to forces to torques to statics.

Centripetal Acceleration & Satellite Orbit Problems

This video covers a variety of centripetal acceleration problems. We start with the basics of the centripetal acceleration formula (a=v2/r). Then we get into common examples: we calculate the speed a roller coaster should go over a 15-m radius hill such that it barely doesn't leave the tracks, and we calculate the velocity a satellite must have to maintain a circular orbit. Fun fact: both examples require setting centripetal acceleration equal to gravitational acceleration(g)!

Centripetal Force vs Centripetal Acceleration

Later in physics, we'll have a bunch of videos on advanced centripetal force problems. This video is only meant to introduce the topic in the way you might see it in the kinematics section of your book, which is where books usually first introduce the centripetal force formula (a=mv2/r). Examples include: how fast you can swing a yo-yo before its string breaks, and the lateral force created by a car going around a turn.

Linear Velocity In Circular Motion

In centripetal acceleration problems, sometimes they just give you velocity (the "v" in a=v2/r). However, often they give you that speed in another form such as RPM (revolutions per minute), Hertz (Hz, revolutions per second), or period of orbit (either orbits per year or years per orbit). This video is about how to convert those funky units into the linear velocity you want (m/s). For more, check out our unit conversion & dimensional analysis videos.