# How do bearings lower friction?

Hi,
The first time I really encountered object with bearings and was wondering about what they really are was about 3 years back when I was on inline skates with a classmate. There was a nice long and smooth downhill and we both drove down without much beforehand added speed. Soon he was going way faster and was still moving many seconds after me. At that point when we started to talk about it, I thought than my inline skates do not have any ball bearings, which I now think is not true, he only had clean ones since his skates were new. Probably without bearings the skates would not work.

Ball bearing. See how they do not slide, they rotate.

Ball bearings are small balls (often from metal) enclosed between two spaces that are supposed to rotate, for example on some axis. It is possible to just leave the two surfaces touching but then they just rub against each other which causes high friction. The important part is that the balls as you can see on the left, rotate, they do not slide and when circular object is only rotating instead of sliding it does not experience much of a resistance. Try it yourself. Take a pencil and toss it across table so that it does not start to turn (parallel with the direction of the movement). Remember the distance where it got and try the same thing but this time perpendicularly and see how far it gets, that is exactly what the bearings are doing.

There are lot of types made for different purposes. Since the bearings have much lower area with which they are touching they do not distribute pressure so well, also they might need cleaning often or lubrication. In fidget spinners you will of course find bearings. The ones that spin very long time are the ones with ceramic bearings.

Dragallur

# Why do formulas look like this?

Hi,
today I want to explain the formula cars and why they look like how they look like, because they have something very special, upside down wings!

Wow, ok, what is that? Well in the picture above you can notice two particular parts which you would not maybe expect when driving as fast as possible since they make the friction with air higher.

There is one infront of the car and one behind it. It is turned towards the motion of the car so that the air pushes the car back and down.

I could seem that it is not very efficient and that it only slows the driver, but lets see the physics behind it!

Formulas have one problem, they have to slow down in curve. Why? Well if they would not slow down it would throw them out of it because of the cars inertia (not centrifugal force). At the same time the driver wants to drive as fast as possible to finish the race first. When he is driving in the curve the only thing that holds him in place is the friction from tires, here it has the role of centripital force and the equation for friction is:

F=Nf

Where N is the downward force and f is the ratio between asphalt and tire. To get the highest possible centripetal force, or friction here, you need to have bigger N.

You would have big N if you would have heavy car but you do not want to have that since it would slow you a lot in straight line. So you put on your car those wings and it looks like this:

The brown arrow is the direction in which the formula drives. Blue arrows are the flow of air this pushes the black part down (red arrow) and little bit back. The simple blue arrow shows where the air goes afterward.

This red arrow helps the car stay on the road because it does not fly away thanks to this even in high speeds, otherwise you would have to slow down because of the inertia.

Dragallur

# How to! 3) Sail against wind

Hi,
if you have ever been on a sailing boat you know this one. How can you sail against wind without using paddles when the force will move you back? There is a way, and it is pretty neat!

Below you can see the picture of boat which is pushed by wind, but what if it wants to go up? There is way called: crossing.

Below you can see how boat can move to up and left. Here the wind is shown by these brown arrows. Blue arrows are friction from water. The thing is that when the sail is like this, wind is trying to push it mostly to left. Have you ever tried to push boat from one of the sides? It is way harder then pushing it from front or back, this is because you need to push the great amount of water that is right behind the boat and also because of friction. So the boat has one more way to go and that is forward, amazing.

If your destination is actually right against the wind you can do the same every once a while but on the other side so you are “crossing”, making your way longer but still effective.

Picture of how the sails must be turned so you can sail in desired direction, you can see that there is a direction in which you can not sail but by changing the direction you can achieve the same thing.

Dragallur