Help with free body diagram for circular motion

AI Thread Summary
The discussion focuses on visualizing a free body diagram for an object on a rotating disk, identifying key forces acting on it: gravitational force (Fg), normal force (Fn), centripetal force (Fc), and static friction force (Ffs). It is clarified that Ffs acts tangentially to the disk's rotation and is equal in magnitude to Fc, allowing the block to remain at rest relative to the disk. When the disk rotates, the frictional force initially points tangentially but later aligns inward as angular velocity stabilizes. The concept of centrifugal force is introduced, emphasizing the balance between this outward force and the inward frictional force in a rotating frame. Understanding these forces is crucial for analyzing circular motion dynamics.
eggman2001
Messages
2
Reaction score
0
Suppose you have an object (lets call it block A) resting on the edge of a circular rotating disk and sitting static on the disk. I'd like to visualize a free body diagram for this showing forces.

These are the forces I believe are acting on it:
- Fg - Force due to gravity
- Fn - Normal force equal in magnitude to Fg but it the opposite direction
- Fc - Centripital force towards the center of the disk
- Ffs - Force of static friction equal equal in magnitude to Fc in the direction that is tangent to the disk and in the same direction as the rotation of the disk.

Is this correct? I'm also trying to understand why Fc and Ffs would be equal in magnitude as I saw in an example.

Any help would be appreciated.
 
Physics news on Phys.org
It is the frictional force which is the centripetal force. Without friction, the body wouldn't stay at rest with respect to the disk.

When the disk starts to rotate, the frictional force instantaneously will be in the direction tangential to the rotation of the disk, and pointing toward the direction of motion of the block. But once the angular velocity has become constant, the direction of the frictional force is toward the centre of rotation.

This can be visualized by going to the rotating frame. There, the block experiences a centrifugal force acting radially outward, which has to be balanced by the frictional force acting radially inward.
 
That makes sense. Thank you.
 
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
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}...
Back
Top