Extended Free Body Diagrams

Torque and the Second Condiction of Equalibrium

Page 3

This text is meant to accompany class discussions. It is not everything there is to know about static equilibrium. It is meant as a prep for class.

BEAM forces

Where beams attach to the wall there exists a pin hinge. The pin hinge exerts a reaction force. This force is broken down into two smaller forces we are calling the vertical force, “V” and a horizontal force “H.” The vertical force, “V,” keep the beam from sliding down the wall. The horizontal force, “H,” keeps the beam from punching through the wall into the building. Identify the reaction force on your free body diagrams and extended free body diagrams two forces.

The weight of the beam is located at the center of mass of the beam. If you were to hold the beam up with one finger, you would lift at the center of mass with a force equal to the weight of the beam. If a beam is described as, "homogeneous," then the center of mass is located in the middle of the beam.

Extended Free Body Diagrams

An extended free body diagram is used to show forces and distances on the same diagram.

This YouTube video can be found at https://youtu.be/hgpmFYXMcW8

Info
Show notes

This information shown below is the non-video, abbreviated,version of the YouTube video above. Click on the, "Snow notes," tab.

	This is what a typical problem might look like. It will have some forces that do not all act at the same location.
	This is the diagram that shows more than the picture that was given. The cable indicates a tension on the beam. The fact that the beam has mass indicates that is has weight pulling it down. The "R" force is new. It is the reaction force of the wall. This force does two things. If pushes to the right to keep the beam from puncturing the wall and it holds the left end up.
	This is the first diagram you write on the paper. Make it large! Notice that is missing all force components. The body is no longer a dot. It is now a line that shows horizontal distances.
Click here to see the solution to the example problem.	This is the second diagram you write on the paper. Make it large. Use about half the width of the paper. To highlight the differences in the two diagrams the components are shown in red.

To have any value, you need to try the example problems before looking at the solutions.

Question
Paper Solution

Draw an extended free body diagram of the beam for the diagram shown below. The beam is homogeneous and has mass.

Solution

Question2
Paper Solution

Draw an extended free body diagram of the beam for the diagram shown below. Each mark on beam stands for 1 foot of distance.

Setup image

Here are two possible solutions. There are more... The difference is where the pivot point is placed. The top solution places it on the right. The bottom solution places it on the left. Both solution will work.

The solution below shows the distance as being measured from the other left instead of the right. The distance's starting point can be anywhere.

by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)

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