Coefficient of rolling friction question

In summary: I don't know, accuracy?Personally I might want to choose something that relates initial velocity and distance to stopping to try to eliminate time as something that has to be measured with...I don't know, accuracy?
  • #1
Draggu
102
0

Homework Statement



Describe how you could use the procedure from this experiment to measure the coefficient of rolling friction between the tires of a car and the road surface for different pressures of air in the tires?

Procedure =
1. Slide a mass along the surface of a lab desk and release the mass at a preselected "starting point"
2. Use a stopwatch and record time/dist taken for the mass to come to a complete stop.


Homework Equations





The Attempt at a Solution



I really have no idea. Any hints would be nice :(
 
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  • #2
Draggu said:

Homework Statement



Describe how you could use the procedure from this experiment to measure the coefficient of rolling friction between the tires of a car and the road surface for different pressures of air in the tires?

Procedure =
1. Slide a mass along the surface of a lab desk and release the mass at a preselected "starting point"
2. Use a stopwatch and record time/dist taken for the mass to come to a complete stop.

I really have no idea. Any hints would be nice :(

All things being equal, if different pressures produce different stopping distances what can you say about acceleration? And if there are different accelerations - that would be due to what?
 
  • #3
Err, the car tires with more pressure will accelerate faster than the one's with less pressure.
 
  • #4
Hi Draggu! :smile:

Assume it's the same as ordinary friction …

what equation relates the stopping distance (from a particular speed) to the coefficient of friction?
 
  • #5
Well, I read the question over and over and I guess it's trying to say that if we put more/less pressure in the car, it can help measure the coefficient of friction?? If the tires have more pressure they weigh more (more air) but they also would roll faster than tires with less pressure, and less weight. But! Newtons law states that Force= mass* acceleration

Or, Force of Friction = coefficient of friction * mass * gravity

I just don't get it! and I have no idea what equation relates to that, tiny-tim. I'm just crappy at physics I guess
 
  • #6
Draggu said:
… I guess it's trying to say that if we put more/less pressure in the car, it can help measure the coefficient of friction??

Perhaps I'm missing the point :redface:,

but I don't think they're asking you to theorise about how the pressure affects it …

just to measure the effect :wink:
 
  • #7
Draggu said:
Err, the car tires with more pressure will accelerate faster than the one's with less pressure.

So long as you are keeping in mind greater acceleration here means less deceleration. What you are measuring of course is negative acceleration - i.e the slowing down kind of acceleration. Firmer tires will roll longer yes? (Consider the extreme case of flat tires for instance.)

From kinematics then you can determine what each distance means wrt the slowing deceleration and isn't that then a result of your friction?
 
  • #8
LowlyPion said:
So long as you are keeping in mind greater acceleration here means less deceleration. What you are measuring of course is negative acceleration - i.e the slowing down kind of acceleration. Firmer tires will roll longer yes? (Consider the extreme case of flat tires for instance.)

From kinematics then you can determine what each distance means wrt the slowing deceleration and isn't that then a result of your friction?

I understand in theory how it works, but I do not know how to calculate it... I just don't get it.
 
  • #10
LowlyPion said:
You're looking for a kinematic equation then:
https://www.physicsforums.com/showpost.php?p=905663&postcount=2

One that yields a from distance and velocity perhaps?

Ok, so I would roll tires with different pressures, measure the distance they each covered and the time it took, then use d=v2t-(1/2)at^2 to calculate a. The force of friction (Ff) will be the MASS of the tire times the acceleration. Fn will be the force of gravity times the mass (9.8)(x)

then the coefficient of friction will be Ff/Fn , and it will be negative, or positive?
 
  • #11
Draggu said:
Ok, so I would roll tires with different pressures, measure the distance they each covered and the time it took, then use d=v2t-(1/2)at^2 to calculate a. The force of friction (Ff) will be the MASS of the tire times the acceleration. Fn will be the force of gravity times the mass (9.8)(x)

then the coefficient of friction will be Ff/Fn , and it will be negative, or positive?

Personally I might want to choose something that relates initial velocity and distance to stopping to try to eliminate time as something that has to be measured with precision.
 
  • #12
LowlyPion said:
Personally I might want to choose something that relates initial velocity and distance to stopping to try to eliminate time as something that has to be measured with precision.

In the original experiment we used time anyway. But that being said, is my formulae correct?
 
  • #13
Draggu said:
In the original experiment we used time anyway. But that being said, is my formulae correct?

Sure. If you have the time and distance and know the initial velocity then you can figure the a.
 
  • #14
As to whether μ is positive or negative ... it will always be positive (and usually less than 1 ... usually). It's basically a ratio of 2 weights right?
 

1. What is the coefficient of rolling friction?

The coefficient of rolling friction is a dimensionless quantity that represents the resistance to motion of an object rolling over a surface. It is defined as the ratio of the force required to keep the object rolling to the weight of the object.

2. How is the coefficient of rolling friction determined?

The coefficient of rolling friction can be determined experimentally by rolling an object of known weight over a surface and measuring the force required to keep it rolling at a constant speed. This process is repeated for different weights and the coefficient is calculated as the average of these values.

3. What factors affect the coefficient of rolling friction?

The coefficient of rolling friction is affected by several factors, including the type and roughness of the surface, the weight and shape of the object, and the speed at which it is rolling. Other factors such as temperature and the presence of lubricants can also impact the coefficient.

4. How does the coefficient of rolling friction compare to other types of friction?

The coefficient of rolling friction is typically lower than other types of friction, such as static or sliding friction. This is because rolling motion involves less surface contact and therefore less resistance to motion. However, the coefficient of rolling friction can vary greatly depending on the factors mentioned above.

5. How is the coefficient of rolling friction useful in real-world applications?

The coefficient of rolling friction is an important parameter in many engineering and industrial applications, such as designing tires for vehicles, calculating the energy efficiency of rolling objects, and predicting the wear and tear on machinery. It is also used in sports equipment design, such as in determining the optimal surface for a golf ball to roll on.

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