Direction of static friction between a vehicle and circular dome

[alyssam042]

Homework Statement

Someone is riding a motorcycle in horizontal circles inside the surface of a large dome with radius R. They have a constant velocity v, and are located at angle θ above the ground. Draw a free body diagram including static friction.

Relevant Equations

None

So the only problem I am having is determining the direction of static friction. I did the same problem but while they were going in a vertical circular motion instead, where the static friction force was in the direction of centripetal force (pointing to the center of the circle).

Would it be the same in this case as well? Since the motorcycle is not going in a horizontal circular motion at the center of the dome, I have the normal force pointed perpendicular to the surface like normal. But what about the static friction?

 

[haruspex]

going in a vertical circular motion instead, where the static friction force was in the direction of centripetal force (pointing to the center of the circle).

I fail to see how the static friction, which is necessarily tangential, could ever point radially.

determining the direction of static friction

Please be specific about what possibilities you think you have narrowed it down to.

 

[alyssam042]

I fail to see how the static friction, which is necessarily tangential, could ever point radially.

Please be specific about what possibilities you think you have narrowed it down to.

From what I understand, the static friction is usually what "supplies" the centripetal force, and causes radial acceleration.

I do not have it narrowed down to much unfortunately, I'm not sure if it would be normal to the path or just completely parallel to the path of the dome possibly.

 

[alyssam042]

Here is a diagram if that helps

 

[jbriggs444]

Here is a diagram if that helps

That is a diagram. It is not a "free body diagram" since it does not show any forces.

 

[kuruman]

I did the same problem but while they were going in a vertical circular motion instead, where the static friction force was in the direction of centripetal force (pointing to the center of the circle).

I think you are confusing the normal force and the force of static friction. In the vertical circle problem it is the normal force that provides the centripetal acceleration. By definition, the force of static friction is always parallel to the surface and the normal force is perpendicular and away from the surface. Can you add these two forces plus gravity in your drawing to address the issue that @jbriggs444 brought up in post #5? Drawing gravity and the normal force first should help you figure out how to draw the force of static friction.

 

[alyssam042]

That is a diagram. It is not a "free body diagram" since it does not show any forces.

I know. That is just a diagram the HW problem gave me, which is why I called it a diagram, not a free body diagram.

 

[haruspex]

From what I understand, the static friction is usually what "supplies" the centripetal force, and causes radial acceleration.

I can think of a situation like that, but I don’t think I've ever seen it in a physics exercise.

I know. That is just a diagram the HW problem gave me

This forum requires that you show some attempt, so draw a free body diagram of the motorcycle-and-rider 'rigid' body, then try to answer as many of these questions as you can:

What forces act on it?
What are the directions of those forces, as far as you can determine?
If the motorcycle were on a level road, what would be the possible directions for friction between tyre and road?
What is the body’s acceleration (magnitude and direction)?

Please post your FBD.

 

[kuruman]

I can think of a situation like that, but I don’t think I've ever seen it in a physics exercise.

Car going around in a circle on a flat horizontal surface at constant speed?

 

[haruspex]

Car going around in a circle on a flat horizontal surface at constant speed?

Doh!