# Solving Problems with Rolling & Slipping: Help for Friction Confusion

• dev70
In summary: If the sphere is sliding without rolling, then friction is not acting and only the linear acceleration is caused by gravity and the normal force.In summary, the conversation is discussing the concept of friction in classical rotational mechanics. It is stated that if a body is rolling without slipping and its velocity of center of mass remains constant, there is no friction acting on the body. This can be observed in real-life examples, such as a train with solid steel wheels maintaining a constant velocity. However, in certain situations, such as a sphere rolling and sliding down an inclined plane, friction may or may not be acting depending on whether the sphere is rolling without slipping or sliding without rolling.
dev70
hi pf, the more i think i have understood classical rotational mechanics the more it turns out to be clumsy? i am just not able to understand the slipping and rolling of bodies? somewhere friction comes into play and somewhere dont?
"if a body rolls without slipping such that velocity of COM doesn't change then no frictional force acts on the body" how? why would a body roll if there is no friction?

dev70 said:
why would a body roll if there is no friction?
It's not about how it started rolling. Once it is rolling at constant speed no friction is necessary.

What AT said.

It actually says that in the quote...

"if a body rolls without slipping such that velocity of COM doesnt change then no frictional force acts on the body"

Consider a train that has solid steel wheels (so negligible rolling resistance)... When it accelerates it applies a force on the track in one direction, when it brakes it applies a force in the opposite direction. When it does neither and travels at a constant velocity no frictional forces are acting.

Aside: In a real train this isn't true because of things like wind resistance and rolling resistance isn't totally zero. So some force (and power from the engine) is required to maintain a constant velocity.

ok..if i consider a sphere rolling as well as sliding down an inclined plane? what should i interpret? friction is acting or not?

dev70 said:
ok..if i consider a sphere rolling as well as sliding down an inclined plane? what should i interpret? friction is acting or not?
If the sphere is rolling without slipping down the incline then there must be a friction force to produce the angular acceleration.

## 1. What is the difference between rolling and slipping?

Rolling is a form of motion where an object moves along a surface while rotating, whereas slipping is when an object slides along a surface without rotation. Rolling is usually associated with circular objects, such as wheels, while slipping can occur with any type of object.

## 2. How does friction play a role in rolling and slipping?

Friction is the force that resists motion between two surfaces in contact. In rolling, friction helps to maintain the rotation of the object, while in slipping, friction acts in the opposite direction and slows down the object's motion.

## 3. Can rolling and slipping occur at the same time?

Yes, it is possible for an object to experience both rolling and slipping motion simultaneously. For example, a car's tires can roll forward while also slipping slightly on a wet road.

## 4. How do you calculate the force of friction in rolling and slipping?

The force of friction in rolling can be calculated using the coefficient of rolling friction, the weight of the object, and the radius of the rolling object. In slipping, the force of friction can be calculated using the coefficient of sliding friction, the weight of the object, and the angle of the surface.

## 5. What are some real-world examples where understanding rolling and slipping is important?

Understanding rolling and slipping is important in many industries, such as transportation and manufacturing. For example, engineers need to consider rolling and slipping when designing tires for vehicles or when developing machines that use rolling motion to move objects. It is also important for athletes to understand rolling and slipping when using equipment such as skates or skateboards.

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