# Homework Help: Moment at 2 ends of beam

1. Jul 6, 2016

1. The problem statement, all variables and given/known data
in the first diagram , i notice that the moment is constant throughout the beam...

why in the second notes, for the moment 20kNm at 2 ends of beam, why the moment varies from -20kNm to 0 from one end to another end?

2. Relevant equations

3. The attempt at a solution
Which is correct? Which is wrong?
i'm confused....
another thing that i noticed is why no matter moment is clockwise or anticlockwise, the moment is always -20kNm??(as we can see ,moment is anticlockwise on the left , clockwise on the right....)

2. Jul 6, 2016

### SteamKing

Staff Emeritus
You can't compare beams willy-nilly. The support conditions influence how the forces and moments distribute within the beam.

In the first case, you have a cantilever beam, with the left end fixed and a couple applied at the opposite end. In order to maintain static equilibrium, there will be a constant moment present along the length of the beam, as shown in Fig. (b). The fixed end of the cantilever has a reactive couple, which combines with the applied couple to make a zero net moment for the beam.

In the other two beam cases, the beam is pinned at each end and a couple of magnitude 20 kN-m is also applied at each end. Pinned connections cannot support a moment, so the moment diagram shows the magnitude of each couple where it is applied and a zero moment at the opposite end of the beam, with a linear slope in between.

3. Jul 6, 2016

why moment at the opposite end of the beam will be 0 ??? why not positive 20kNm ???

4. Jul 6, 2016

### SteamKing

Staff Emeritus
I explained that in my post.

If you are not going to read the replies to your questions, what are you doing on this site?

5. Jul 6, 2016

why not positive 20kNm ??? why it's 0 ? we can see , the moment 20kNm at the left ( anticlockwise) is opposite to the moment on the right (clockwise)