Hard Torque Problems That Combine Torque with Linear Forces (& Multiple Objects)

General Advice on Fancy Torque Problems

The hardest thing about crazy torque problems with masses hanging off of each other: where to start? Since the problems in the other videos in this chapter take so long to solve, sometimes the forest gets lost for the trees, so in this video I slow things down to look at "the view from 30,000 feet" to see what all these problems have in common and the two or three tricks then all require.

Initial Angular & Linear Acceleration of Beam Falling when Pivot On One End

In this video we calculate the acceleration that would be felt by a small spider or lady bug who happened to be hanging out on a hinged beam if it suddenly starts swinging downwards towards the floor.

Find Acceleration of Mass Hanging From String Wrapped Around Solid Disk

In this problem, worlds collide... The mass will fall in a straight line like any other hanging mass and will therefore need ΣF=ma to calculate its acceleration. The wheel is in its own world of rotations and moments of inertia, so its world is governed by ΣΤ = Iα. How can these two worlds unite to allow us to solve for acceleration?

Find Spin Rate of Gyro Toy Pulled By A String

This problem only has one mass, thank goodness, but it's pretty tough because it also unites the worlds of linear and rotational physics: How does the linear pull of a string turn into rotational velocity? And how do we convert between the length of the string and the corresponding angular quantities? Is it even possible?*

*just kidding, I explain it in the video

Find Tensions In Strings When Two Different Masses Hang From Wheel

This is the toughest one! THREE objects, so you need THREE free body diagrams, each with their own coordinate axes that need to match up and use the right hand rule. And worst of all, one of the objects is rotating. Start with a fresh sheet of paper for this one!

Find Final Velocity of Falling Beam Using Energy

We return to the beam problem, but instead of looking at the instantaneous acceleration at the moment of release, we instead calculate final velocity after the beam has rotated downwards. If you aren't sure what potential energy and kinetic energy are, skip this video for now because there will be lots more rotational energy videos later in physics.