Not just in a car’s context, but more generally. Like what about a curved surface makes things roll better? I’m so confused
In: 1
Take a block. Sharpie the center of the block. Roll it.
The point that you marked moves up and down, and its motion is very jerky. Large sudden forces act upon the block to make this path possible, and at higher speeds those forces grow very quickly.
The same is not true for a rolling circle. The center moves in a perfectly straight line, but even the non-center points follow nice and smooth sinusoidal curves. No jerky motion, no strong forces, and so very little energy lost.
There are 2 important features of a circle that make them roll so well on flat surfaces. And the flat surfaces part is very key, as what I’m about to say is not exactly the case for less uniform surfaces.
One key feature is that circles are continuous and differentiable, meaning there are no gaps in a circle and that any single point along the circle has only one possible tangent line. This is important because the ground will always lie tangent to whatever part of the circle is touching it. This means there’s always a smooth transition from point to point along the circle’s edge as it moves forward, given that there is no sharp angle around which the shape would have to “pivot” as it rotates.
The next is that each point along the perimeter of a circle is the same distance from the center, meaning there would be no jarring up and down movements for a person using the circle as a wheel as it rolls ahead (because they would always be the same distance from the ground).
Again, both of these points rely heavily on the premise that the surface the circle is rolling on is flat. There are lots of cool examples of non-circular wheels that make for a totally smooth ride on different surfaces! Tricycles with square wheels is a classic – https://youtu.be/LgbWu8zJubo
Edit: added “continuous” along with differentiable for extra specificity
<Sorry for my English (I’m dyslectic non-English)>
Build a small wagon with square wheels and push it along a road for one mile. You will notice that at the beginning that wagon will jerk up and down. After one mile you will notice that the jerking is less pronounced, and pushing the wagon forwards is easier.
A close at the wheels will reveil that the corners of the wheels got rounded.
After more miles the pushing gets easier and easier, until the wheel is completly round.
I got that idea from: *The Flying Sorcerers by David Gerrold& Larry Niven*
The wheel can make constant contact with a flat surface because all points are at the same distance from the center, so your center stays at the same height. But a wheel will not do as well on a non-flat surface. So for example your road surface is a series of bumps of an exact shape. The surface of each bump is the same length as a side of your square (yes, square) wheels. You will ride nice and evenly over that surface, while you’d be bumping like crazy with round wheels. This is because the surface plus the square wheels kept your center at the same height.
Latest Answers