# Tag Info

### Should the coin be heavier or lighter in the coin drop experiment?

Most of the answers here are missing the fact that the mass of the coins alters how much force has to be applied to the card in order for the coins to fall into the glass. If the force applied to the ...
• 6,516

### Calculating stopping distance of a car on an inclined plane with friction

From this point, you can just utilise the kinetic equation to find the stopping distance such that: $$v^2_f=v^2_i + 2ax$$ $$0 = v^2_i+2ax$$ And solving for $x$ we get: $$x=-\frac{v^2_i}{2a}$$ ...
Accepted

### What does Feynman mean here about static and sliding friction?

In the lubrication case, in the real world as two surface slide over each other there are hydraulic effects that cause the coefficient of friction to drop signicantly with velocity before gradually ...
• 5,020
Accepted

### Rolling resistance uphill

The rolling resistance depends on the normal force on the plane, wich is $W*g*cos(\alpha)$ with $\alpha$ the angle of the inclined plane.
• 6,440

### How does a vehicle's brake affect the friction between the vehicle and ground?

While answering another question, I found a neat way to think about this problem. What you are essentially asking, is how does the force applied by the brakes reach the ground. I think that root ...
• 12.5k
1 vote

### Braking distance vs. mass of the vehicle

You may think of wheels as an extension of the road, on which you can grip more comfortably and apply the brakes indirectly. On each of the wheels during braking, two forces are acting. One between ...
• 12.5k
1 vote

### Braking distance vs. mass of the vehicle

A really simple model which assumes no air resistance and using newton's laws and work energy theorem will give you a formula for braking distance of $d = \frac{1}{2} v_{final\,velocity}^2/ \mu g$. ...
1 vote

### Direction of friction of a block moving down a plane

Kinetic friction will always oppose motion, not other forces. A good tip is to always remember friction (kinetic or static) as a force that tries to prevent motion as its only purpose. So, the ...
• 51.6k
1 vote

### Direction of friction of a block moving down a plane

friction will oppose the component of gravity acting along the ramp That's not a given. That's just a consequence of some situations where that force is "trying" to move the block, but ...
• 41.3k
1 vote
Accepted

### Direction of friction of a block moving down a plane

If it’s kinetic (sliding) friction the friction force will act parallel to the surface and opposite to the motion of the block already underway. If it’s static friction the friction force will again ...
• 74.2k

### A paradox while explaining the equilibrium of books

Not all friction forces labeled $f$ in the sketch are identical. I fact, they become smaller as you move towards the centre on the stack. Realizing this removes all of the mentioned issues. The ...
• 51.6k
Accepted

### A paradox while explaining the equilibrium of books

You are correct, in a scenario with an even number of books there will be no friction acting between the pair in the middle. To see this, take the simplest case - two books. The force $F$ applied by ...
1 vote

### Tension of rope over frictionless edge obstructing block

I would consider each bent part a point of interest. Starting at the last bend before the hanging mass, let's fix the rope on the edge and calculate the tension for this segment. Call it $|T_2|=mg$. ...
Accepted

### In an ideal situation, why should no friction exist when an object rolls?

Imagine a small car sitting on flat pavement. The car is in neutral, and the wheels are straight. The goal is to push the car as far as possible in one minute time. You would likely choose to push the ...

### In an ideal situation, why should no friction exist when an object rolls?

The "point of contact" is a mathematical concept. It does not have any mass, so it is not, strictly speaking, a physical object. Two other things relevant that you didn't ask but are ...
• 1,028