Why wheels help things move faster

A gentle turning force at the edge of the wheel can be used to make a stronger turning force near the middle of the wheel. An axle is a rod that passes through the centre of a wheel. In a road vehicle such as a car, the engine turns the axle to make the wheels go round. The edge of the wheel moves around more quickly, but with less force than the centre of the wheel. As described in more detail in my comment, you can't use the standard Amontons-Coulomb AC model of friction for rolling resistance.

As far as I can tell from wikipedia , an appropriate relation for rolling resistance can be written in the form.

Four wheels would give a certain amount of friction per wheel, which would be multiplied by four. Therefore the result appears to be that the three-wheeled vehicle would be faster. If fewer wheels give better efficiency, the question would be why we don't all ride around on unicycles. For train locomotives, the large number of wheels is so that the locomotive can be heavy and get good traction without damaging the tracks.

Friction is what keeps the wheels from spinning i. Removing a wheel adds more strain friction to the axes, probably making the car slower keep in mind that the 4rth wheel still has some friction even though it is removed. Each wheel needs to be as lightweight as possible compared to the weight of the car, so all the kinetic energy goes into forward motion of the car, not into rotary motion of the wheels.

That is an argument for fewer wheels. At the same time, larger wheels will have less rolling friction than smaller ones. The wheels need to have a hard outer surface, not rubber, so you don't lose energy flexing the rubber. The wheels need to spin easily with as little friction as possible, and not wobble. Like if you spin them with your finger, they should continue spinning for a while, and not get into a wobbling action that will really create friction.

The weight of the car should be more toward the front, for directional stability. If the weight is toward the rear, the slightest sideways force will tend to turn the car, making the sideways force worse and causing the car to slide against the side of the track.

In airplanes this is called a ground loop. ADDED: As I think about it, it might even make sense to go down to just two wheels, to reduce rotational energy even more. Then have the weight slightly forward of the axle, and have a teflon or low-friction skid in front. Think of it like a dragster car - most of the weight on the wheels in back, very little in the front. In my experience with Pinewood Derby cars, the issue is that there are several sources of friction: the friction of the wheel against the "axle" nail , but also the friction of the wheel against the body of the car, and the wheel against the guide strip on the center of the track.

The retarding torque that the latter two can create can be quite significant. Making sure that the wheels are well aligned and that the point of contact with the car is well lubricated is essential. Similarly, anything you can do to maintain the alignment of the car with the track lateral stability can have a large positive impact.

As for the basic question 3 vs 4 wheels: I suppose that it would be easier to align 3 wheels than 4 - and in that sense the three wheeled solution has a chance of being faster. However, I am pretty sure that any three wheeled solution will have less lateral stability - and if the car has a tendency to shift left and right, the friction from the side of the wheels against the track and against the car all quickly become the dominant force.

As for rolling friction: there is a non-linear factor in "real" friction problems, which argues in favor of spreading the normal force over more wheels. This is because when a wheel deforms, the contact area goes up with force assuming a constant "pressure" inside the tire , but the size of the deformed region volume of tire that is deformed during contact goes up faster than the contact area.

This means that there will be relatively more power dissipation in a heavily loaded wheel vs two more lightly loaded wheels.

This is an effect that is negligible for a pinewood derby car - but it is very real on large vehicles with inflated tires and heavy loads. In those situations, more wheels is better.

Lots of wheels to spread the load. This limits the force per wheel, and thus the distortion of not only the wheels, but of the road surface. Fewer wheels means each wheel "sinks deeper" into the road below, and tho would mean that the wheel is always "rolling uphill" - a significant factor in rolling friction for heavier objects. Friction at the axles would work in favor of the 4 wheeled vehicle more friction per axle while wind resistance would work in favor of the 3 wheeled vehicle more surface area.

The funny thing about wheels is that we are used to seeing them in use all around us but they are a man-made thing. Before the invention of the wheel people had to pull or push things along the ground. It is thought the possibly the original wheels were actually round branches from trees and that humans later perfected the concept of the wheel and then the wheel and axle. The earliest civilization that is known to use the wheel was found as evidence in an area known then as Samaria in 4, B.

They had a very sophisticated culture and archeological evidence shows that they were just beginning to relocate and live in cities.

The original wheels were circular only, with the development of the addition of spokes later. Wheels bring a mechanical advantage by allowing you to turn something heavy through the use of an axle that is attached to the heavy item.