How to Reduce Friction

What You Need to Know

Force is a push or pull on an object. Friction is the force that opposes the motion of objects whose surfaces are in contact with each other. A ball bearing is a sphere that not only supports but also rotates in order to reduce friction between moving parts. A lubricant is a substance used to reduce the friction between two solid surfaces.

How Does Friction Work?

Friction is a force that resists motion. The amount of friction depends on how an object is moved, such as by sliding it or rolling it. When two things slide, the friction between them is greater than if they roll over each other. For example, it would be much more difficult to pull a wagon on grass if it had skis instead of wheels. In the figure on page 115, muscle force is used to pull the wagon. At the same time, the force of friction between the skis and the surface they move across, the grass, is trying to make the wagon stop. As the force of friction increases, more force is needed to move the wagon. The amount of friction also depends on how rough or smooth the surfaces of the objects moved are. The wagon with skis would be much easier to pull on snow because the surface of the snow is smooth. When things in contact move, the rougher their surfaces the greater the friction.

What Does This Have to Do with Ways to Reduce Friction?

There are many ways to reduce friction between objects. Lubricants, such as oil, reduce friction by filling in surfaces, making them smoother. Ball bearings rotate to reduce friction between objects by changing sliding friction to rolling friction.

Fun Fact

The osprey is the only hawk that hunts in water. It looks for fish that feed at the surface of the water. When the osprey is airborne, it turns the captured fish headfirst, which reduces air friction as it flies. Its claws also have spiky Velcrolike pads that increase friction and help the bird keep a firm grasp on a slippery wet fish.

Real-Life Science Challenge

Even though friction opposes motion, it also helps objects to start moving. For example, friction between a bicycle tire and a road helps the tire to grip (to hold onto) the road. If the road is covered with ice, there is so little friction between the tire and the ice that the tire slips and spins freely, and the bicycle is not able to move. Engineers are challenged to design tires with many features, including high static friction (the bonding of two objects at rest) and low rolling friction (the friction between a rolling object and a surface). The tires must also flex to fit road irregularities and yet be rigid enough to minimize heat buildup. These are accomplished by choice of materials, tire design, tread design, inflation pressure, and many other factors.

Experiment

Now, start experimenting with friction. How can it be reduced?

Hints

• Design a method for measuring friction such as:
  • The rate at which objects move.
  • The amount of force it takes to move objects using a spring scale or a scale you designed.
• Test different methods for reducing friction on a specific object.

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