# Friction of spheres & cylinders

• sudhu37
In summary, a spherical wheel has less rolling resistance than a cylindrical wheel, but it also has less contact area with the road, so it can be more difficult to control.
sudhu37
Hi,

I am doing a project involving spherical wheels. I need some help with regards to the role played by friction on motion of spheres and cylinders (normal car wheels) on roads. Will friction act forward or backwards ?? Which type of wheel would be more advantageous ? Would appreciate any help or inputs to make me move ahead. Thanks

It's meaningless to ask whether friction on a wheel acts forwards or backwards. It will act in the direction which opposes movement.

And which type of wheel would be more advantageous depends entirely upon the application. The only reason that I can imagine to use a spherical one would be in a case such as the 'ball-bots' where rotation in all directions is needed. It would have almost no traction due to the minimal contact area with the road.

Advantageous in what respect? It's difficult to provide feedback if you don't tell us what you are trying to accomplish.

Basically i am making a project based on a solid spherical wheel. I am required to show how this wheel is better than a normal cylindrical wheel in aspects such as friction. Couold i please get some help on this topic, to show that the solid sphere is more beneficial than the circular wheel (based on friction). Thanks.

I can't really think of any reasons the solid spherical wheel would be beneficial over the standard circular wheel for conventional applications, but I can think of a lot of reasons why it wouldn't be. Here's a couple:

1) More rolling mass given the same rolling diameter.

2) Solid sphere will supply no give.

3) Mounting it with an axle through it would make it essentially a standard wheel with a bunch of unnecessary weight.

4) Rolling resistance would only be decreased on VERY smooth surfaces, but on irregular surfaces it would be more difficult to roll.

...

wouldn't a sphere have just as much lateral friction as friction in the direction of travel. limiting a sphere to only level ground. any uneviness or slop would make the wheel turn downhill, or if the slope was too great you would slide downhill just as much as you would traverse. (i think).

if at speed the extra mass of the sphere will cause more gyroscopic effects. making control more difficult.

assume the mass and the radius of both the wheels(sphere and cylider) to be the same.(density of the sphere being low)..hence for the same torque applied on both the wheels , the angular acceleration of the sphere would be greater.would this be a right statement. as moment of inertia of a sphere is less than that of cylinder.

also we are considering the sphere to have an outer coating similar to that of a normal wheel.hence by reducing the pressure, one can attain more than just point contact with the ground.

i wanted to know, how friction would effect the rolling of a sphere?

Since rolling resistance is mostly a property of the materials in the road and tire, I don't think t would be relevant here. Ie, a ball bearing on a smooth steel surface has near zero rolling resistance, but then so does a metal cylinder.

It would also hep to know what type of application we're talking about - a car? A ball bearing?

sudhu37 said:
assume the mass and the radius of both the wheels(sphere and cylider) to be the same.(density of the sphere being low)..hence for the same torque applied on both the wheels , the angular acceleration of the sphere would be greater.would this be a right statement. as moment of inertia of a sphere is less than that of cylinder.
Yes. But whether that is beneficial or not is another issue. As someone pointed out earlier, your contact points aren't the same, so your sphere is essentially a cylindrical wheel with a lot of extra, useless material on the sides. Why not just use a narrower wheel?
also we are considering the sphere to have an outer coating similar to that of a normal wheel.hence by reducing the pressure, one can attain more than just point contact with the ground.

i wanted to know, how friction would effect the rolling of a sphere?
Softening a tire is what causes rolling resistance. So the net effect will be that you'll add rolling resistance if you want to soften the tire enough to have the same contact area.

we are using concept of spherical wheels in vehicles for our project. there is no axil running through the wheel. it works with rollers holding the sphere in place. we would like to know if this wheel will have more or less friction when it is put on the road. will more or less friction be adventageous?

would softening the tyres add to the rolling resistance or help to provide more grip when a vehicle is taking sharp turns?

I don't mean this as an insult, so please don't take it as such. Once you've investigated the incredible amount of calculation and experimentation involved in the design of both tires and suspension geometry, I think you'll realize that the concept of spherical wheels is pretty much a waste of time. I know that I would certainly never ride in a vehicle that was equipped with them.

Another point here, which I let go by a couple of times...
If you are indeed using the same sort of drive/control/suspension system as the ball-bots (like a computer mouse ball), then softening the wheels will cause all sorts of control problems. As soon as they're no longer rigid, they're no longer spherical.

Sudhu. How would your spherical tyres actually work? As Danger points out, you won't really be able to control them, but how do they support whatever is inside them? And as for friction, think of your contact patches; a sphere has a tiny contact area compared with a cylinder.

Some severe 'thinking through' is needed here mate.

Softer tyres increase friction and rolling resistance, but how would you soften a spherical tyre?

sudhu37 said:
we are using concept of spherical wheels in vehicles for our project. there is no axil running through the wheel. it works with rollers holding the sphere in place.
Mouse-ball style. Ok. For certain applications there are obvious advantages to that, but we still don't really know what you are trying to do.
we would like to know if this wheel will have more or less friction when it is put on the road.
From what you describe, most likely more (rolling resistance, anyway).
will more or less friction be adventageous?
would softening the tyres add to the rolling resistance or help to provide more grip when a vehicle is taking sharp turns?

Have you managed to create a system to control a sphere wheel or is this a concept design?

Hi ther, Iam also a person in the virtue of producing a conceptual design in the spherical wheel, the best way to design the car is to look at the audi rsq car. it comes in the movie i-robot and it is a conceptual design of the spherical wheel car, the car has 4 spherical wheels and exactly follows the method of mouse ball rollers for producing motion in the spheres. (ie, one in the x-axis, one in the y-axis, and one in the z-axis on each and every wheel) that becomes 12 output speeds, and each roller has to rotate at diff speed to attain the direction of motion and speed on the balls, so we r going to use 2 gear, 2 motors, connected to a single micro-processor which controls every direction of motion, steering is impossible as far as my knowlegde could search and even it is available the cost is high enough to go off the roof, so the steering for our car is goin to be button system over direction and manual control over accerleration and braking as in normal cars.

The advantages of this concept is 1.Very less power is required to drive the vehicle as contact surface of the balls are minimal and very less force is required to rotate a sphere, 2. Evenly loaded with weight can rotate in all direction remaining inline with the vertical axis of the carried weight and speed of motion, 3. Offers most easy change of direction since it doesn't need to re-align to the movement direction, 4. The anti-over turn funtion of spherical wheels is most advantageous since it doesn't have the stopage of the motion perpendicular to the direction of motion as in the cylindrical wheels, therefore the vehicles can be tall and narrow neglecting the ground clearance and centre of gravity, 5.Sphere wheels can work oblique till 15 degrees 6.Due to its shape,the sphere cdan surmout obstacles from any position,both front and lateral, instead of the traditional wheels which cannot the latral obstacles. 7. Spherical wheels can easily move because each wheel cahnges its directoin independently of the other ones. 8.Very less friction over wheel and road so greater speeds with less power. Disadvantages: 1. Control over slopes is difficult, 2. Irregular sphere can cause problems which can happen due to the irregular contact surface over the roads when in motion. 3. Less friction therefore very diffucult when braking (ABS) 4. When traveling in one direction only one rollers of the three in use, for ex. traveling in forward motion uses only the x-axis rollers, but all the other rollers are also in contact, this reduces the friction between the rollers and the balls which is the essence of frictional drive in this concept and the shape of the ball becomes irreglar easily, this is my concept and iam dying to suceed so any of u brainstroms out there read this reply, give us some thoughts...l

spwheel said:
it comes in the movie i-robot
Consider the source. And, by the way, the movie had absolutely no resemblance to the original book by Enio Binder entitled "Adam Link: Robot". The new version of the Twilight Zone did it properly.

spwheel said:
1.Very less power is required to drive the vehicle as contact surface of the balls are minimal and very less force is required to rotate a sphere,

Does the term 'spin-out' ring a bell? Any racer will tell you that while a smoke-show might wow the crowd a bit, it will lose you the race. You want maximum friction between the tires and the road to actually go somewhere.

Yo Man! if u don't understand the concept i don't blame u its pretty tough to understand... but since u don't i will tell u once more that THERE IS FRICTION between the sphere and the Road, only minimal and that is enough to keep the sphere rotating, and for the spin out, it only occurs when the sphere is deformed or out of shape, i know that it won't happen in this high standarad experiment if u do it with precision, if u can't then don't blame me!

Easy, spwheel. As we discussed earlier in the thread, there is a really good reason why car tires are the shape they are. Yes, a smaller contact area means less rolling resistance, but if that were such a good thing, our cars would all already have bicycle tires.

spwheel said:
Yo Man! if u don't understand the concept i don't blame u its pretty tough to understand...

I believe that I understand it well enough; that's why I think that it's a waste of time. And another aspect of your 'minimal friction' idea that you seem to be overlooking completely is that it would have all the stopping power of a greased pig on Teflon. You'd better hope that you never have to slam on the binders. (Or do you plan to heave an anchor out the window?)

One of the largest issues against spherical wheels is in the infrastructure for cars. The roads we have today would absolutely not stand up to cars with spherical wheels. The contact stresses on both concrete and asphalt would be tremendous. I don't even want to think about a large semi with spherical wheels. We would be going through roads in no time flat.

yah u r right, braking becomes ver diffucult when it comes to sp wheels. we'll all i am working on is giving motion to sphere wheel, but the braking concept is out of my reach and some one has to come with somethin like electromagnetic brakes or somethin like tat wher my knowlegde is zero ther. all i want to do is to give motion to 4 sphere wheels with perfect suspention and some basic braking, i think tats difficult enough, and if this works some experts can help me further, i hope!

its a lost cause spwheel. 4get bout braking, u won't have nuff traction 2 accelerate or go roun da corners, dats wot every1 else said, an they was rite. yahh.

In other words, braking isn't the only difficulty. As everyone has pointed out, you won't have nearly enough traction to give adequate acceleration (propulsion) or cornering. I fail to see any benefits this idea has.

Brewski;
I used to only love you for your engineering knowledge (and for guiding me into PF), but your mastery of learning new languages is amazing.

Posted this in another post but the idea is the same
new here but what about treating it like a round mag lev. buy using a center core of iron or some other metal. and and outer layer of what ever material. you could suspend the tire and also rotate it buy means of manipulation of the magnetic field, Near Zero Friction, No Drive to wheel traction issues and very quick response!

## 1. What is friction and how does it affect spheres and cylinders?

Friction is a force that opposes motion between two surfaces in contact. It affects spheres and cylinders by creating resistance or drag, which can slow down or stop their motion.

## 2. What factors affect the amount of friction experienced by spheres and cylinders?

The amount of friction experienced by spheres and cylinders is affected by the type of surface they are in contact with, the weight or mass of the object, and the force applied to the object.

## 3. How is the coefficient of friction calculated for spheres and cylinders?

The coefficient of friction for spheres and cylinders is calculated by dividing the force required to move the object by the weight of the object. This value is then used to determine the amount of friction experienced by the object.

## 4. What is the difference between static and kinetic friction for spheres and cylinders?

Static friction is the force that must be overcome to initiate motion between two surfaces in contact. Kinetic friction is the force that acts against the motion of an object that is already in motion. In the case of spheres and cylinders, static friction is responsible for preventing the object from rolling, while kinetic friction slows down the object's motion.

## 5. How can friction between spheres and cylinders be reduced?

Friction between spheres and cylinders can be reduced by using lubricants, such as oil or grease, on the surfaces in contact. Additionally, using smoother surfaces or reducing the weight or force applied to the object can also help reduce friction.

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