Friction Direction on Rolling Ball: Am I Missing Something?

In summary, the conversation discusses the direction of friction on a ball that is initially skidding and eventually starts rolling on a flat plane. It is determined that the friction acts to the left on the bottom of the ball, slowing its translation and increasing its angular speed in a clockwise direction. The concept of Moment of Inertia is mentioned, and it is explained that the ball will eventually come to a stop due to rolling resistance and air resistance. The amount of rolling resistance depends on the surface the ball is rolling on.
  • #1
Rmehtany
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2
My question is the following. A ball is initially skidding and eventually starts rolling on a flat plane with friction, and later comes to a halt. Which direction does friction act? (see diagram)

If friction acts to the right, then the translational speed will go up, and that's not right.

If friction acts to the left, then the angular speed goes up, and that's not right as well.

Am I missing something? It seems too simple and I feel like a fool to have to ask this.
 

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  • #2
Rmehtany said:
My question is the following. A ball is initially skidding and eventually starts rolling on a flat plane with friction, and later comes to a halt. Which direction does friction act? (see diagram)

If friction acts to the right, then the translational speed will go up, and that's not right.

If friction acts to the left, then the angular speed goes up, and that's not right as well.

Am I missing something? It seems too simple and I feel like a fool to have to ask this.

If the ball is thrown to the right, and skids and then slowly starts to spin up, it is because the friction is acting to the left on the bottom of the ball. That slows the translation to the right, and spins up the angular speed of the ball in the clockwise direction.
 
  • #3
But then if the angular speed is going up, how can the ball reach static equilibrium
 
  • #4
Rmehtany said:
But then if the angular speed is going up, how can the ball reach static equilibrium

Just like at a bowling alley -- the equilibrium is the ball rolling down the alley floor with some angular velocity and with a translational velocity that is less than it had when first thrown. Losses due to friction is one reason the linear velocity is slower, but there is also the energy that is transferred into the angular momentum of the ball as it spins up. Are you familiar with the Moment of Inertia (MOI) concept yet?
 
  • #5
Yea, I am... Ah, I see, but I still have a problem, if the angular momentum is increasing, how does the ball stop? Does it stop decreasing, and when? I understand that angular momentum increases in the beginning
 
  • #6
It is mainly rolling resistance (and air resistance) that will slowly bring the ball to a stop. If it's rolling on carpet, then the rolling resistance is high, so it stops sooner. If the rolling resistance is low (like on hardwood flooring), then the ball is going to roll a *long* way...:smile:
 
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1. What is the purpose of studying friction direction on a rolling ball?

The purpose of studying friction direction on a rolling ball is to understand how friction affects the motion of a rolling object. This can have practical applications in fields such as engineering and physics, as well as helping to improve our overall understanding of the laws of motion.

2. How does friction affect the direction of a rolling ball?

Friction can affect the direction of a rolling ball by providing a force in the opposite direction of the ball's motion. This can cause the ball to slow down or change direction, depending on the surface it is rolling on and the amount of friction present.

3. Are there any factors that can influence the direction of friction on a rolling ball?

Yes, there are several factors that can influence the direction of friction on a rolling ball. These include the type of surface the ball is rolling on, the weight and shape of the ball, and the speed at which it is rolling.

4. How can studying friction direction on a rolling ball be applied in real life?

Studying friction direction on a rolling ball can be applied in real life in various ways. For example, understanding the effects of friction can help engineers design more efficient machinery and vehicles, while physicists can use this knowledge to analyze the movement of objects in different environments.

5. What are some common misconceptions about friction direction on a rolling ball?

One common misconception about friction direction on a rolling ball is that friction always opposes the direction of motion. While this is often the case, it is not always true and can depend on various factors, as mentioned in question 3. Additionally, some people may think that friction only slows down the motion of a rolling ball, but it can also cause it to change direction or speed up in certain situations.

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