0.14 Phy1110: force -- moments, torque, couple, and equilibrium  (Page 2/13)

Supplemental material

I recommend that you also study the other lessons in my extensive collection of online programming tutorials. You will find a consolidated index at www.DickBaldwin.com .

General background information

Creation of tactile graphics

The module titled Manual Creation of Tactile Graphics explains how to create tactile graphics from svg files that I will provide.

If you are going to have an assistant create tactile graphics for this module, you will need to download the file named Phy1110.zip , which contains the svg files for this module. Extract the svg files from the zip file and provide them to your assistant.

Also, if you are going to use tactile graphics, it probably won't be necessary for you to perform the graph board exercises. However, you shouldstill walk through the graph board exercises in your mind because I will often embed important physics concepts in the instructions for doing the graph boardexercises.

In each case where I am providing an svg file for the creation of tactile graphics, I will identify the name of the appropriate svg file and display animage of the contents of the file for the benefit of your assistant. As explained here , those images will be mirror images of the actual images so that your assistant can emboss the image from the back ofthe paper and you can explore it from the front.

I will also display a non-mirror-image version of the image so that your assistant can easily read the text in the image.

Also in those cases, I will provide a table of key-value pairs that explain how the Braille keys in the image relate to text or objects in the image.

Conditions for equilibrium

You learned in earlier modules that the vector sum of all forces acting on a body must be zero in order for that body to be in equilibrium. There is asecond, equally important condition for equilibrium:

The sum of all torques acting upon a body in equilibrium measured about any axis must be zero.

A see saw toy

When I was a child, virtually every playground meant for children had one or more tows commonly called see saws. I never see them any more. They haveprobably been banned as a safety hazard along with swings and other toys.

Hopefully you have had the privilege of riding on a see saw, because riding on a seesaw can provide several different physics lessons.

A simple device

A see saw is a simple device. It can be as simple as a long board balanced on a fulcrum near the center. A child sits on each end. As one child goes down, theother child goes up. Each child uses their feet to propel their end of the board upward. When one end goes up, the other end goes down.

It's the negative acceleration that hurts

Even under the worst of conditions a see saw can prove to be a good physics lesson for a child. The lesson begins when the child on one end jumps off whilethe child on the other end is high in the air. The remaining child suddenly begins a free fall toward the center of the earth with an acceleration ofapproximately 32.2 feet/sec^2.