# Why is this Joint in Tension

1. Nov 30, 2013

### NoobeAtPhysics

1. The problem statement, all variables and given/known data

Determine whether each joint is in tension or compression

2. Relevant equations

sum of force = 0

3. The attempt at a solution

On Joint I, I don't understand why IH is in tension. The pin is exerting a horizontal force and therfore IH should be in compression to oppose the Joint force. This should be the same for Joint IA right since the pin is also exertng a vertical force?

If we look at Joint A, this logic (sorta) makes sense. The roller joint is exerting only a horizontal force and therefore Joint AB must be in compression to oppose this force.. but then there's joint AH which should be in tension to oppose Joint AB...

Any help would be soo great

2. Nov 30, 2013

### Simon Bridge

Build the stricture with drinking straws and blue-tack as see what happens.
As it sits, the whole structure wants to pivot about point A right? (Well, if we hold A.)
So that means that IH is being pulled away from I.

3. Dec 1, 2013

### haruspex

Sure, but which way?