# Method of virtual displacement

1. Dec 28, 2011

### ham_revilo

http://img267.imageshack.us/img267/9636/qw5e64a2d1sda54.png [Broken]

Hi guys. i have a question that needs verification. Referring to the above diagram,

Please determine the Moment, M (Nm) needed in order to hold the mechanism in equilibrium state as shown above by using "Method of Virtual Displacements" or also known as "Method of Virtual works".

I'm referring to this book, Engineering Mechanics:statics. i cant seem to use its formula and concept to apply into my question because im not really good in that particular chapter.

FYI, i already tried using free body diagram ("Total Moment=0" concept) to resolve it but I need some other method to verify my answer. The only other method i found is Virtual Works. if you have any method to calculated it, do comment.

Thanks :)

Last edited by a moderator: May 5, 2017
2. Dec 29, 2011

### Studiot

God, morning, Ham

The rules here need you to show/explain some working even if wrong before obtaining help.

One thing puzzles me.

Your diagram appears to show two links connected by three pinned joints to each other, to a roller at the right hand end, and to a fixed support at the left hand end.

It also shows a moment M applied at the pinned joint between the fixed support and the first link.

3. Dec 29, 2011

### ham_revilo

so sorry. didnt notice there are rules like that here. my intention was getting new ideas or ways to look at this thing and calculate it.

anyhow, following the book, i manage to come out with a equation but im kinda stuck now.
http://img16.imageshack.us/img16/2465/1231245794.png [Broken]
can anyone here differentiate x and θ. a, B, H are constant. i need to derive it into δx in respect of δθ

about your question, im not sure if i understand you correctly, but this mechanism is very similar to the crank mechanism. the first link on the left which is fix to the support is the crank. and the link bar on the right is the linkage. so, yes, there will be a moment in between both bar.

i need to calculate the moment at point "M" is because there will be a motor mounting on point M to drive the whole mechanism. Hence, i need to know the moment/torque in order to select and buy a correct motor.

Last edited by a moderator: May 5, 2017