Direction of reaction of a roller

[werson tan]

Homework Statement

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?

Homework Equations

The Attempt at a Solution

 

[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.

 

[werson tan]

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.

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

 

[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.

 

[haruspex]

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

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.

 

[insightful]

for no 5 , why the recation force acts upward only ? why not also downards?

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.