# Homework Help: Direction of reaction of a roller

1. Oct 23, 2015

### werson tan

1. The problem statement, all variables and given/known data
for no 4 , why the reaction force also act downwards ? as far as i know roller can only support the surface perpendicular to it upwards .... but not downwards...
for no 5 , why the recation force acts upward only ? why not also downards?

2. Relevant equations

3. The attempt at a solution

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2. Oct 23, 2015

### AndrewHolowack

From what I read it looks like figure 4 is describing a roller or a pin. The pin would be the one with the downward force. The figure isn't that clear but I think that's what it's showing.

3. Oct 23, 2015

### werson tan

why The pin would be the one with the downward force?? i thought the support is 'stucked' betwwen 2 surfaces so , depending on the situations , there will be times that the force act downwards , and also there will be time that the forces act upwards

4. Oct 23, 2015

### AndrewHolowack

Your right I wasn't looking at the figure properly. It's a pin and roller between two surfaces so yes depending on the situation the reaction force could be either.

5. Oct 23, 2015

### haruspex

You seem to have answered your own original question here. Do you still have a question regarding no. 4?
I'm not at all sure what mechanism is depicted in no. 5. The image is not very clear.

6. Oct 23, 2015

### insightful

The "rocker" can be thought of as a section of a roller pinned to the end of the rod, so same result as no 3.