Coefficient Of Friction (Circular Motion)

AI Thread Summary
The discussion focuses on the coefficient of friction in circular motion, distinguishing between static and kinetic friction. Static friction applies when an object is stationary relative to another surface, while kinetic friction occurs when there is relative motion. The confusion arises when static friction is used to calculate maximum speed in circular motion, despite it typically being associated with stationary objects. It is clarified that in cases like a car tire, the contact surface can remain stationary while the object moves, necessitating the use of static friction. Additionally, the topic of rolling resistance in ball bearings is introduced, highlighting the need to treat it as a separate type of friction.
Air
Messages
202
Reaction score
0
This is the concept that I am understanding for coefficient of friction. Static coefficient of friction is one which refers to friction which is considered when the object is stationary relative to the other contact object. Kinetic coefficient of friction is one which refers to the friction which is considered when the object is in motion relative to the other contact object.

But, I've come across many question in circular motion which talk about static coeffient of fricition even though it's asking about calculating maximum speed. If static coeffient of friction is when the object is stationary then why is it used to calculate speed, acceleration in circular motion (Surely, we consider coefficient of kinetic friction)? Does the concept differ in circular motion?
 
Physics news on Phys.org
Kinetic friction only occurs when contact surfaces slip against each other--thus the surfaces are in relative motion. Sometimes an object as a whole can be moving, yet the contact surface will not move with respect to the ground. For example, a car can move while the part of the tire in contact with the ground is always at rest with respect to the ground. As long as there's no slipping (or skidding) the only friction you need to worry about is static friction.

Feel free to give a specific problem that we can look at in detail.
 
As for a specific problem, what about a ball bearing for example. I have a wheel rim attached to an axle via a ball bearing. How would I calculate the friction between the bearings? Is that Kinetic friction?
 
The ball bearing will roll on the axel and on the housing - no slipping so it is STATIC friction.
 
Right. So if the wheel rim is free spinning (in the air), what are the forces acting against it? I now assume there is static friction between the housing and axle, I would also think there is some form of rolling resistance between these 2 components as well?
 
ZachGriffin said:
As for a specific problem, what about a ball bearing for example. I have a wheel rim attached to an axle via a ball bearing. How would I calculate the friction between the bearings? Is that Kinetic friction?

Bearings are pretty different from the OP question. Ball and roller bearings have to be treated in terms of their rolling resistance, which is best treated as a separate kind of friction. See, for example,
http://evolution.skf.com/zino.aspx?articleID=14959
 
Last edited by a moderator:
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

A problem from a physics national competition
Replies
13
Views
1K
Why is the direction of kinetic/static friction up a ramp?
Replies
7
Views
1K
How can we model a rolling truck on an incline using rotational motion analysis?
Replies
24
Views
2K
Does coefficient of kinetic friction depend on speed?
Replies
16
Views
5K
Is friction really always related to the normal force?
Replies
5
Views
2K
Finding the time it takes for two stacked blocks to travel
Replies
18
Views
3K
Truck carrying a box, friction problem
Replies
10
Views
5K
Having a hard time learning Newton's 2nd law
Replies
5
Views
2K
Physics help to measure friction
Replies
23
Views
3K
Car that undergoes non-uniform circular motion
Replies
1
Views
1K

Hot Threads

Recent Insights

Back
Top