 In this video I'm gonna go over why you need shear and bending moment diagrams for beams and how you draw them. Beams can fail due to different reasons. One of them is due to vertical loads. These external vertical loads can cause shear. The shear can then vertically crack those beams. In order to design a beam that can withstand the shear of these vertical loads we need to draw the shear force diagram. This diagram will allow us to identify at which location we get the maximum shear so we can then choose the beam dimensions accordingly. Here we have an example of a load on a beam. The first step is as before we have to find the reaction forces of the supports. The second step is we draw the shear force diagram with the position along the beam on the x-axis and the shear along the y-axis. We start on the left side of the beam and we simply travel towards the right. Before we encounter an upwards force we plot it on the shear force diagram in upwards direction whenever we encounter a downward force in downwards direction. So we start from left to right, we encounter the force on A, then nothing happens for a long while so we just keep traveling and plotting a horizontal line until we encounter the first downward force which in this case is the load, then we go by the amount of that force down and then we keep going horizontally until we hit the next upward force which was the force at the support B and we have our shear force diagram. Now we can use that diagram to find where the maximum shear occurs. Here that was between the load and the right support. Another possible failure of beams is due to torque. External torques can cause internal bending moments which then break the beam. Similar to the shear force diagram we now gonna draw a bending moment diagram to find the location of the biggest bending moment and then once again select the beam dimensions accordingly. The first step of the bending moment diagram is actually to draw the shear force diagram. Once we have the shear force diagram we can start the bending moment diagram by plotting the area under the shear force diagram from left to right. This is the same thing as integrating the shear force along the x axis. So we start on the left and whenever we have a positive area we plot it upwards, so in this case my area is increasing so I keep going up and if we have an area that's below the x axis we go downwards. Note that in the bending moment diagrams unless you have torques on each end of the beam you should be starting and ending at zero so it's a good double check if your diagrams are correct. Now we can easily find where the maximum bending moment happened. Here that was exactly at the location the load was applied. With this maximum bending moment we then go into some lookup tables to find the dimensions of the beam that we need.