Kill my curiosity - Rolling a ball down a ramp, friction or no friction?

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Hello people,
I have 2 scenario's. One is a ball rolling down a ramp with friction, onto pavement with friction. The other is a ball rolling down a ramp without friction, onto pavement with friction. Everything between them is the same except for the friction.

I think that having no friction will mean the ball will go further. I say this because you won't lose any energy to friction. The ball will only have translational energy, until it hits the pavement then a torque will be introduced, and this will cause it to start rolling.

On the other hand, with friction it will start rolling on ramp, and rolling things go further. But we will lose more energy due to friction. I don't know why, and i guess part of what i want to know is why do things that roll go further. We will lose more energy due to friction. SO i'm not sure how this affects each other.

What i want to know is which ball will travel further, and will there velocities at the bottom be the same?

I am not a physics student, but i have a taken 2 mechanics courses, and i know about angular momentum, moments of inertia, and angular velocity. I am really curious about this.

Thank you for your time.
 

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  • #2
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Hello people,
I have 2 scenario's. One is a ball rolling down a ramp with friction, onto pavement with friction. The other is a ball rolling down a ramp without friction, onto pavement with friction. Everything between them is the same except for the friction.

I think that having no friction will mean the ball will go further. I say this because you won't lose any energy to friction. The ball will only have translational energy, until it hits the pavement then a torque will be introduced, and this will cause it to start rolling.
Yes, The ball #2 will only have translational energy and in the process of its rotation speed increasing from 0 to [tex]\omega[/tex], much energy lose.
On the other hand, with friction it will start rolling on ramp, and rolling things go further. But we will lose more energy due to friction.
No. If it(#1) just roll and dont slide on ramp, then NO energy will be lost. it is because of static friction doing no work.

I don't know why, and i guess part of what i want to know is why do things that roll go further. We will lose more energy due to friction. SO i'm not sure how this affects each other.

What i want to know is which ball will travel further, and will there velocities at the bottom be the same?
the smoth one's translational velocity is larger than the first ball at the bottom. As for the rotation velocity, they reversed. and their energies are same at the bottom.

I am not a physics student, but i have a taken 2 mechanics courses, and i know about angular momentum, moments of inertia, and angular velocity. I am really curious about this.

Thank you for your time.
In THEORY, they can roll for ever on plane with friction, because when the translational speed match up the rotation speed ( [tex]\upsilon=\omega R[/tex] ), there are no friction between the rolling ball and the rough plane.

if someone would do the experiment, I prefer the first ball (on rough ramp) will go further.
 
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  • #3
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So from what the previous person said, i think it comes down to, how do we determine how far something goes with X amount of kinetic energy, and with an Y amount of rotational energy.
 
  • #4
The second ball cannot purely roll as the point of contact of the ball with the ramp has an acceleration
 
  • #5
While purely rolling a ball does not lose energy to friction as the point at which friction acts loses contact instantaneously and hence displacement is zero. Rolling objects lose energy for some other reason, which I am unable to recall.
 
  • #6
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Fiction causes loss of energy, simple as that. If you were to give a rotation to the ball on the frictionless ramp it will continue to rotate without loss of energy.

You can think of fiction as if the ramp was sticky. As the ball is rolling it sticks(slightly, it doesn't stop the motion) to the ramp. This is what allows the ball to start rolling in the first place.

If there is enough fiction the ball will come to a stop quickly and possibly even just stick there. A rolling ball has inertia though which will help it continue rolling.

You don't need a ramp for your experiment. Just roll two balls with one having some part of it's path being frictionless.

It's obvious that the the ball on the frictionless path will travel further because that is the whole point of friction. Friction resists the motion. If it resists it then it slows it down and if it slows it down then there must be a loss of energy.

@ashishsinghal: The point of contact is very complex and it is not instantaneous. It's not even well defined. Basically like minute Velcro. The fact that it has friction though means that you are losing energy.

Can you think of something that has friction and doesn't lose energy due to the friction?

From wiki
"
Friction is not a fundamental force but occurs because of the electromagnetic forces between charged particles which constitute the surfaces in contact. Because of the complexity of these interactions friction cannot be calculated from first principles, but instead must be found empirically."

So unless you can beat the electric force your "Contact" point isn't instantaneous(because this force doesn't need contact to act).
 
  • #7
When a sphere rolls ,the surface in contact with the sphere &horizontal is depressed and the surface just in front of it is raised ,so when the rolling sphere strikes this raised surface the normal reaction instead of passing from center of mass ,passes through a little bit away in the forward direction of the motion.It therefore opposes the motion of the body.

Torque produced by friction is in the direction of angular velocity. How can it stop it?
 

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