Friction: A Force That Opposes Motion

Friction: A Force That Opposes Motion

The Source of Friction

Friction occurs because the surface of any object is rough. Even surfaces that look or feel very smooth are actually covered with microscopic hills and valleys. When two surfaces are in contact, the hills and valleys of on surface stick to the hills and valleys of the other. This contact causes friction even when the surfaces appear smooth. The amount of friction between two surfaces depends on many factors, including the roughness of the surfaces and the amount of force pushing the surfaces together.

Rougher Surfaces Create More Friction

The rougher the surface, the more microscopic hills and valleys there are on that surface. Thus, the rougher the surface, the greater the friction. Pavement is much rougher than grass, so more friction is produced when you slide on it. The increase in friction helps stop your sliding, but it is also very painful! Contrary, if the surface is smoother there is less friction.

Types of Friction

The friction you observe sliding books across a tabletop is called sliding friction. Other types of friction include rolling friction, fluid friction, and static friction. The name of each type of friction is a big clue as to the conditions in which they can be found.

Greater Force Creates more friction

Friction Types

The amount of friction also depends on the force pushing the surfaces together. If force is increased, then the hills and valleys can come in even closer contact. This causes the friction between the surfaces to increase. Less massive objects exert less force on surfaces than more massive objects do. However, changing the amounts of the surfaces that touch does not change the amount of friction.

• Sliding Friction- If you push an eraser across your desk, the eraser will move a short distance and then stop. This is an example of sliding friction. Sliding friction is very affective at opposing the movement of objects
• Rolling Friction- If a heavy dresser were put on wheels, you would have an easier time moving it. The friction between the wheels and the floor is an example of rolling friction. The force of rolling friction is usually less than the force of sliding friction.
• Fluid Friction- On wet floor, the sliding friction between your feet and the floor is replaced by fluid friction. The term fluid includes liquids and gases.
• Static Friction- When a force is applied to an object, but the object doesn't move it is called static friction. The object doesn't move because the force of static friction balances the force applied

Friction Can be Harmful or Helpful

Think about how friction affects a car. Without friction, the tires could not push against the ground to move the car forward and the brakes could not stop the car. Without friction, cars are completely useless. However, friction can also cause problems in cars too. Friction between moving engine parts increases their temperature and causes the parts to wear down.

Some Ways to Reduce Friction

One way to reduce friction is to use lubricants. Lubricants are substances that are applied to surfaces to reduce friction between them. Some examples of common lubricants are motor oil, wax, and grease. Friction can also be reduced by switching from sliding friction to rolling friction. Another way to reduce friction id to make that surface rub against each other smoother.

Some Ways to increase Friction

One way to increase friction is to make surfaces rougher. For example, sand scattered on icy roads keeps cars from skidding. Baseball players sometimes wear textured gloves