Rolling Resistance vs Speed

[e2m2a]

I have conducted an experiment which involves measurements of the velocities of a carriage moving in a straight line which has 4 polyurethane caster wheels attached to it. (The kind you can get a hardware store.) In one phase of the test the carriage is pushed at about .1 meters per second. In the second phase the carriage is pushed about .3 meters per second. The carriage is rolling over a level smooth surface of Masonite. The mass of the carriage including the wheels is 2.3 kg.

My question is will the rolling resistance between the wheels and the Masonite be significantly different when the carriage is rolling at .1 meters per second vs rolling at .3 meters per second or would the rolling resistance be pretty much the same at both speeds?

 

[jack action]

At those speeds and with this type of wheel, you can assume the rolling resistance to be independent of speed. Only the normal force will matter.

 

[Merlin3189]

Jack's probably right. But if you're doing the experiment, I'd have thought you'd find out. Experiment trumps assumptions. If you need to assume speed doesn't matter, by all means do so. If your experiment can measure any difference, why assume?

 

[kuruman]

Question: Do you assume rolling without slipping? Polyurethane on masonite sounds slippery to me. Here is what I understand by rolling resistance.

 

[berkeman]

4 polyurethane caster wheels

the rolling resistance between the wheels and the Masonite

IMO, there is very little rolling resistance due to the interface between the wheels and the Masonite floor. Both are hard and do not deform much (unless your load is crazy heavy). The "rolling resistance" will be mostly bearing friction in the wheels, IMO, and should not vary much with velocity. Please do share your test results with us so we can check how it went. Thanks.

 

[berkeman]

4 polyurethane caster wheels attached to it. (The kind you can get a hardware store.)

In one phase of the test the carriage is pushed at about .1 meters per second. In the second phase the carriage is pushed about .3 meters per second.

BTW, were these caster wheels free to yaw from side-to-side, or were they fixed in the direction of movement? If they can yaw, then the rolling resistance can change with velocity due to oscillations in the direction that they are pointing as you push the cart. Just think of a shopping cart with one bad front wheel caster...

 

[e2m2a]

At those speeds and with this type of wheel, you can assume the rolling resistance to be independent of speed. Only the normal force will matter.

Thanks for your answer.

 

[e2m2a]

Jack's probably right. But if you're doing the experiment, I'd have thought you'd find out. Experiment trumps assumptions. If you need to assume speed doesn't matter, by all means do so. If your experiment can measure any difference, why assume?

Yes. Experiment is the final say on anything.

 

[e2m2a]

BTW, were these caster wheels free to yaw from side-to-side, or were they fixed in the direction of movement? If they can yaw, then the rolling resistance can change with velocity due to oscillations in the direction that they are pointing as you push the cart. Just think of a shopping cart with one bad front wheel caster...

Thanks for your answer. The carriage moved in a straight line. The wheels were the stationary kind. No wobbling.

 

[e2m2a]

IMO, there is very little rolling resistance due to the interface between the wheels and the Masonite floor. Both are hard and do not deform much (unless your load is crazy heavy). The "rolling resistance" will be mostly bearing friction in the wheels, IMO, and should not vary much with velocity. Please do share your test results with us so we can check how it went. Thanks.

Someday I might be able to share the full test results on this site.

 

[sophiecentaur]

My question is will the rolling resistance between the wheels and the Masonite be significantly different when the carriage is rolling at .1 meters per second vs rolling at .3 meters per second

Something that you may actually be able to measure is the amount of distortion that the load causes to the wheels. The particular material combination may make it hard to do but measuring the amount by which the axle drops when the load is applied may be possible, using a camera or a sensitive micrometer perhaps. The amount of drop is the equivalent of the wheel going uphill by that amount each rotation and a lot of that energy could be lost (depending on the hysteresis, which could also be measured). The Power lost in that way would be proportional to the speed. Soft car tyres get much hotter because of this distortion effect.

It has been suggested, above, that you should experiment as much as possible and this could be worth considering.

Rolling resistance on railway tracks: I saw a travel programme on the TV last week about a long, rural railway line in Sri Lanka. They showed a guy walking the line, oiling it with a mop (every day?) on the grounds that it reduced corrosion, wear on the bends and resistance. It made me wonder if it was actually necessary (keeping someone employed, perhaps) or why that couldn't be done by all trains as they went along the track. The tiniest spray of oil would cost very little. I had never heard of this practice anywhere else,