# Rolling Fricition, Kinetic Friction

1. Jan 7, 2016

### Prannoy Mehta

Does rolling friction depend on the surface area? In other words, the size of the object placed? If I had a block and sphere of the same mass. Without static and kinetic friction coming into play. Which would experience greater rolling friction if they were on the same incline and of the same material and mass?

If I had a similar scene with a cube and cuboid (The base area of the cuboid is more, they are made of same materials and have the same mass.). Which would go down first if kinetic friction is considered? Assuming no toppling.

2. Jan 8, 2016

### Staff: Mentor

Are you picturing your block smoothly rolling down the incline?

3. Jan 8, 2016

### Prannoy Mehta

Yes. Toppling over and over again. (With a good speed) Giving a picture that it is rolling.

4. Jan 8, 2016

### Staff: Mentor

That sounds like a combination of sliding and rolling, at least.

5. Jan 8, 2016

### Prannoy Mehta

Yes, very true. I forgot about it. So I will reframe my first question.

Does rolling friction depend on the surface area? In other words, the size of the object placed? If I had two spheres (With radii r1 and r2. r1>r2) of the same mass. Without static and kinetic friction coming into play. Which would experience greater rolling friction if they were on the same incline and have similar forces between the atoms of one another? (I mentioned the latter condition to simply ensure that there is nothing to do with the interatomic forces between the atoms of the spheres with that of the plane. As the materials will be different. If not appropriate please modify the condition to convey the same message.)

6. Jan 11, 2016

### Staff: Mentor

If the wheels on a railway freight car were swapped with wheels similar but of a greater diameter, how will its rolling resistance be expected to change? .... does that say what you seek?