# Tag Info

### Solving a problem regarding a block sliding down a ramp

For both ascent and descent the positive axis for displacement, velocity and acceleration is taken as down the slope. So $a$ is positive in both cases. (We expect the value of $a$ to be different for ...
• 26.6k
Accepted

### Solving a problem regarding a block sliding down a ramp

Friction opposes the actual or impending motion of the body it acts upon. The effect can at first seem counter-intuitive. For example, when your foot (or a wheel) pushes on the ground to move ...
• 7,036

### Solving a problem regarding a block sliding down a ramp

Friction does not always act in direction opposite to motion. When car accelerates, nothing can act on it but friction force acting on wheels. Or when you move on your legs it is friction force which ...
• 137
Accepted

### Friction forces in an idealized model of hydroplaning

I suspect the idea is to consider that the water film is experiencing Couette flow, with boundary constraints such that the flow speed is $u$ at the point of contact with the tire and $0$ on the point ...
• 3,055
Accepted

### A Friction Problem (Experimentation)

Friction between the die and the ground is almost entirely irrelevant to this phenomenon. If the die has enough energy after the collision with the ground to lift its center of mass high enough to ...
• 9,840
Accepted

### Why static friction is necessary for pure rolling instead of kinetic friction?

My confusion is that why is static friction necessary for pure rolling instead of kinetic friction. The short answer has already been given to you in some of other answers. Pure rolling involves no ...
• 58.3k
Accepted

### Role of static friction in rolling

I’m not sure what you mean by “move angularly”, but the static friction force, when present, acts perpendicular to the radius of, say, a wheel at the point of contact with the surface producing a ...
• 58.3k
Accepted

### Does the Hubble expansion cause apparent friction?

The effect is real, and happens for the reason you describe, but it is a kinematic process, not frictional. Peebles mentions it in Principles of Physical Cosmology and calls it "velocity sorting&...
• 19.4k
1 vote

### Does the Hubble expansion cause apparent friction?

The relativistic momentum $p=mv\gamma$ relative to a local observer comoving with the Hubble flow is inversely proportional to the growth of the scale factor $a$: \frac{p_0}{a(t)} = \frac{p(t)}{a_0}\$...
• 8,753
1 vote
Accepted

### Centripetal Force Acting on a Belt and Pulley System

The circular motion applies to the part of the belt that is in contact with the motor pulley (there is a similar section undergoing circular motion on the drum pulley also). the centripetal force is ...
• 1,806

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