Why is rolling friction less than sliding friction?
Question
December 18, 2008
why rolling friction is less than sliding friction?explain with figure
Anup - Nepal
16975
Answer
The easiest explanation why rolling friction is less than sliding friction is to consider when you rub things together. There is a resistance against rubbing since the surfaces grab on each other. With rolling friction, there is only one small area in contact with the other. Plus the rubbing is at a minimum. This rolling friction is less.
An automobile is travelling with constant foward acceleration,which point of a tire has a greatest absolute acceleration relative to the ground.
kidia - Tanzania
16775
Answer
The top of the tire is moving forward twice as fast as the automobile is moving. The bottom of the tire is on the ground and is not moving with respect to the ground.
why do the tyres of racing bikes make very thinly? the reason shouldn't be the friction as i understand. because the friction doesn't depend on the square area of the tyre. please send the answer as soon as possible.
Paramee - Sri Lanka
14271
Answer
With tires, the friction is a function of the area of contact on the ground, because of the distortion of the tire. Racing bicycles have thin tires with rounded bottoms to reduce the amount of tire on the surface. They also are under high pressure to further reduce the amount of distortion. Another minor factor for the thin tires and wheels is the lower the weight of the bike.
See our lesson on Rolling Friction at: http://www.school-for-champions.com/science/frictionrolling.htm
In a train engine, what types of friction is acting in drive wheeles and in which direction. What type /direction of friction acting in the rolling wheels of the add on compertments. Since frictional force is directly proportional to normal reaction, how tractive force generated in engine drive wheels are able to pull add on compertments whose cumulative weight is much more than engine weight. Regards
Sanjay Mitra
Sanjay - India
14228
Answer
The train or locomotive engine wheels use static friction to move the train forward. If they go too fast, they start to slide and kinetic friction is must less than static friction, so it is difficult to move forward. See the lesson on the Role of Friction in Starting Rolling Motion at: http://www.school-for-champions.com/science/frictionrolling_start.htm for an explanation.
The rolling friction of the steel wheels in the other train cars on the steel track is very small. There is more friction in the axles of the wheels.
The weight of the cars or compartments does not affect the resistive force of friction very much, since the rolling friction is so small. The initial movement of the driving wheels must be such that they do not slide, and they will be able to overcome the inertia of the numerous compartments.
I am trying to build a pedal power car that weighs approx 3300 lbs. I will be pedaled on a very flat dry lake bed. There will be 4 people pedaling and I am trying to figure out the gearing. If you can provide any help that would be greatly appreciated.
Erick
Erick - USA
13452
Answer
I'm not sure I could help you with the gearing, but you might check out the work done on many of the fastest bicycles:
Could you help me solving the following problem: A car is driven at constant speed v along x -axis. All wheels are rolling without slipping. If we look a rim point of one wheel, it's speed varies from 0 to 2v with respect to ground. Does this rim point have any x or y -axis acceleration with respect to ground or the center of wheel. For me, it seems obvious that the rim point should have acceleration but so far I have not found any equations or evidence from literature that this is the case. Could you explain that what is the truth?
Thanks and Best Regards,
Ari - Finland
12462
Answer
If you marked a spot on a wheel rim and observed it as it rolled by, you would see the spot follow a sine wave or cycloid with respect to you. A point on the outer surface would follow a sine wave, while the point on the rim of the tire would be a flattening out distortion of that sine wave. A point on the axis would follow a straight line.
Thus, a point on the rim accelerates in an oscillating manner in the y-axis or vertical axis with respect to the ground. In the x- or horizontal axis, it also accelerated according the the motion of the sine wave in that direction.
The view from the center of the wheel is that the point on the rim is moving at a constant speed, but it is accelerating with a change of direction, up and down, forward and backward.
Dear sir I need your help in the following question. Lets assume a wheel of a car weighs 500kg while is rolling on the pavement at one point compresses a hydraulic cylinder, when this cylinder is fully compressed is the same level as the pavement, the cylinder to be fully compressed needs 300kg of vertical pressure, the wheel is 500kg. My question is would the compression of this cylinder will make the vehicle to consume more energy or is it energy transfer of the weight of the wheel to the cylinder like if we stepped onto weight scale, If the vehicle needs extra energy fuell due to rolling friction because will compress the cylinder how can we calculate this.
Stefanos - Canada
12161
Answer
You need to know the height of the cylinder above the ground and the radius of the wheel.
When the wheel strikes the cylinder only a component of it will be pushing downward, while the cylinder will act as resistance to the forward motion of the wheel. As the wheel and rolls forward more and more force will be pushed down on the cylinder and less resistance will be seen by the wheel. Using a drawing with vectors is a good way to visualize the situation.
It seems the resistance of rolling friction should increase with velocity because there is more deformation per unit of time. Or is it that more power is required, e.g. force times distance? Please clarify. Thank you.
Frank - USA
11961
Answer
With softer materials like tires, the friction should increase with velocity.
If the speed is constant, the resistive force of friction is constant and the work required (force times distance) is dependent on the distance the tire rolls. The power relates to the energy expended per unit time.
dear sir, i would like to congratulate you on coming up with such a wonderful site for students. it has been of immense help to me ... i ve a doubt regarding the acceleration of an automobile. my doubt is how to find out the time reqd for any vehicle to reach a specific speed starting from rest..? i thought like this: assuming mass of the vehicle as 'm' and the specified speed as 'v'. the KE of the vehicle is .5*m*v^2. call this value as 'a'( in kilo joules) now the vehical manual or tech-specifications says that the vehicle can generate a max of 'b' horsepower at some rpm. converting 'b' to b1(kilo watt). now if t=a/b1 then is 't' the time i was looking for .there will be some losses definatley, but is this approach right?? i request you to answer my question. thanking you Rakshit.Shetty India
Rakshit - India
11691
Answer
If an automobile has a constant acceleration "a", then the time it takes to achieve a velocity v is t = (v - vi)/a, where vi is the initial velocity. Since vi = 0, t = v/a.
This is the common problem given in physical science classes.
But you are looking at a solution of a more complex situation, where you need to know the weight and friction of the vehicle, horsepower and such. Unless some of those variables were given in the problem, the solution is the simple one.
Wants to study rolling friction with different materials
Question
March 11, 2006
Dear Sir, I have been navigating the web trying to find information about rolling friction but have been unsuccessful. My question is the following: Supposing I have a metal wheel mounted on an axle in a device that can determine rolling coefficients. Now, installing flat bands of different synthetic materials around the wheel's rim of said wheel, I want to know: what rolling coefficients would I find for each material? I can imagine these coefficients would have an intermediate value between that of steel-on--steel systems (0.001), and that of car tyres, which are close to 0.015. What I want to find out is whether some synthetic rubbers have a regenerative behaviour whereby the rolling coefficient lowers sharply. If this happens, then the questions would be: what is this material and what is the thickness of this band relative to wheel's diameter at which this phenomenon takes place? Thanking you in advance, I shall be looking forward to hearing from you soon,
Daniel - Argentina
10406
Answer
Getting a device to on the axle to measure rolling coefficients or friction may not be that easy. But measuring rolling friction can be done similar to that of sliding friction. Using a vehicle with the wheels to be tested, you can push or pull the vehicle with a sensitive scale. The force required to maintain a constant speed would be the rolling friction plus the friction of the axles. The wheel or tyre materials are varied, while the axle friction remains a constant that can be calculated out.
Note that the surface that the wheels roll on must be the same for all tests.
Rolling friction for various rubber materials probably are a function of speed, temperature, weight of the vehicle, thickness of the material, and the diameter of the wheel. You need to keep all but one constant for a series of tests.
I don't have any data on materials or what would happen in these tests. It sounds like an interesting experiment, and I would be curious to see what results you get.
Do you have any questions, comments, or opinions on this subject? If so,
send
an email with your feedback. We will try to get back to you as soon as possible.
Feel free to establish a link from your website to pages in this site.
