rolling friction

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engineering frictional resistance to rotation or energy losses in rolling bearingsCompare sliding friction
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012


What does rolling friction mean?

Rolling friction is the force that resists rolling objects.

Friction is the resistance present when two surfaces rub against each other. Friction is caused by multiple factors, such as attraction between molecules or uneven surfaces coming into contact with each other.

Besides gravity, friction is the main force that causes something to stop moving if you stop pushing it. For example, if you try to slide a heavy box across the floor, friction will make it harder to move the box. If you stop pushing, the box will most likely stop moving almost instantly (depending on weight). The type of friction opposing your sliding the box is called sliding friction.

But what about objects that roll? Rounded objects, such as wheels, spheres, and cylinders, don’t move across surfaces the same way sliding objects do. The movement of these objects is opposed by rolling friction. The force of rolling friction is much smaller than that of sliding friction, which is why a heavy box on wheels is much easier to move than a heavy box on the floor.

The main cause of rolling friction is the energy lost when surfaces indent when contacting each other. If you sit on a bicycle, for example, the bottom of the tires flatten a little as your weight pushes them against the road. As the tires turn, they will expand out again. At the same time, the road will also indent very slightly as the weight of you and the bike pushes against it. This causes a very small, uneven surface, which allows for friction. All of this combines to result in a small loss of energy as the bike moves, which results in rolling friction.

That’s why if you roll a ball down an endless hallway, it will eventually stop rolling. Rolling friction will resist it the entire time and will gradually slow the momentum of the ball until it stops moving completely.

Why is rolling friction important?

The first records of the term rolling friction come from around 1839. People have understood the existence of rolling friction for much longer, though, perhaps all the way back to the 1400s.

The mathematical formula to calculate rolling friction is:

Fr = μrN

Fr is the force of rolling friction. N is the force of the object being moved. In simple scenarios, N is equal to the combined weight of the wheel and the object on top of the wheel. μr is the coefficient of rolling friction. This dimensionless number varies widely and depends on many factors, including the dimensions, surface shape of the wheel, and surface of the ground. Rolling friction, then, will change depending on multiple factors, such as a treaded tire versus a smooth tire and pavement versus ice.

Did you know … ?

The study of friction is known as tribology. The man credited as the founder of tribology, and one of the first people to study rolling friction, was Leonardo da Vinci. Da Vinci was a Renaissance man who was as fascinated by engineering and science as he was by art.

What are real-life examples of rolling friction?

While the term rolling friction is often used in physics classrooms, the concept is also important when designing cars and other things that involve rolling.


What other words are related to rolling friction?

Quiz yourself!

True or False?

In general, the force of rolling friction is much smaller than sliding friction.

How to use rolling friction in a sentence