How do ball bearings reduce friction? They reduce friction by turning sliding motion into rolling motion.
If you have ever used a fidget spinner, you know that once you give it a spin and let go, it will keep spinning for far longer than you would expect. This is all down to the ball bearings that are inside it and it is because ball bearings reduce the amount of friction on the spinning part. Everything on Earth experiences friction because even if an object is not touching another surface, we still have an atmosphere, and air resistance is a type of friction.
Friction is a force that opposes movement. It is a force between two surfaces that are sliding across each other. Fiction always works in the opposite direction to the direction the object is trying to move in. No surface is completely smooth, and when you try to slide one object across another object, the bumps on one surface come into contact with the bumps on the other surface and catch. To free the one object from the other object requires work, which requires energy. The energy comes from the kinetic energy that the object has and is released as heat. That is why something sliding across one surface slows down, and why you can create heat by rubbing one material on another. The object you are moving only has a certain amount of energy. That might be energy from your hand if you are pushing something. As it moves, the energy it has slowly dissipates until it has no more energy to move. If you want the thing to keep moving, you need to put more energy in.
Sometimes we want things to have friction. We want friction between the soles of our shoes and the floor, for example, so that we can walk. If you have ever tried walking on an ice rink, you know what it is like to have reduced friction between the soles of your shoes and the ground. It is very difficult to stay upright. However, a lot of the time, we want to lower friction as much as possible. If you are driving a car, the friction between the tires and the road surface, along with the friction between the car and the air, means that you have to put in more energy to keep the car moving. If you can reduce friction, objects can move with less energy. There are several ways you can reduce friction. Oil is an excellent way. The oil fills the dents and bumps between the two surfaces, meaning they can slide over each other without needing as much energy. Water works as well. You could also make a vacuum. That doesn’t remove the friction between the surfaces, but it does remove the air resistance. Or, and this is today’s question, you could use ball bearings.
Ball bearings work to reduce friction in a way that not even tires on a car can do. Ball bearings are made of solid steel, and they are polished to have a very smooth surface. They reduce friction because of four things. The first is that they are rolling. If you are sliding one object over another object, all of the energy has to go into pushing the one object while the other tries to stop it. If you have something that can roll, less energy is needed to keep it rolling than if you have something that is flat. That is why cars have wheels. The second thing is that only a small surface area of the ball bearing is in contact with the lower surface at any one time. Because friction is caused when two surfaces move against each other, reducing the size of one surface will reduce the friction. The third reason is that they are very smooth. Ball bearings are precision milled and then polished until they are as smooth as possible. Reducing the number of dents and bumps on the surface will reduce the amount of times it catches on the second surface and will lower the friction. And the fourth reason is that they are very hard. A car tire has many of the same attributes as a ball bearing, but it is not as hard and is compressed by the weight of the car. This increases the surface area that is in contact with the ground and increases the friction. Cars with flat tires are less economical than cars with fully inflated tires. Ball bearings are very hard and don’t compress. Because of all these reasons, ball bearings have very low friction. Then, coupled with those things, they are usually lubricated with oil or grease as well, which further reduces their friction. And this is what I learned today.
Sources
https://blog.slsbearings.com/how-ball-bearings-reduce-friction
https://en.wikipedia.org/wiki/Ball_bearing
https://www.bbc.co.uk/bitesize/articles/zxqrdxs
https://www.twinkl.jp/teaching-wiki/air-resistance
Photo by Marcelo Avila: https://www.pexels.com/photo/silver-bracelet-with-balls-19911427/