# friction

## factors that affect friction

Rougher surfaces have more friction between them than smoother surfaces. Thats why we put sand on icy sidewalks and roads. You cant slide as far across ice with shoes as you can on the blades of skates (see Figure 1.4). The rougher surface of the soles of the shoes causes more friction and slows you down. Q: Heavier objects also have more friction. Can you explain why? A: Heavier objects press together with greater force, and this causes greater friction between them. Did you ever try to furniture across the floor? Its harder to overcome friction between a heavier piece of furniture and the floor than between lighter pieces and the floor.

## friction produces heat

You know that friction produces heat. Thats why rubbing your hands together makes them warmer. But do you know why? Friction causes the molecules on rubbing surfaces to move faster, so they have more energy. This gives them a higher temperature, and they feel warmer. Heat from friction can be useful. It not only warms your hands. It also lets you light a match as shown in the Figure 1.5. On the other hand, heat from friction between moving parts inside a car engine can be a big problem. It can cause the car to overheat. Q: How is friction reduced between the moving parts inside a car engine? A: To reduce friction, oil is added to the engine. The oil coats the surfaces of the moving parts and makes them slippery. They slide over each other more easily, so there is less friction.

## what is friction

Friction is a force that opposes motion between any surfaces that are touching. Friction can work for or against us. For example, putting sand on an icy sidewalk increases friction so you are less likely to slip. On the other hand, too much friction between moving parts in a car engine can cause the parts to wear out. Other examples of friction are illustrated in the two Figures 1.1 and 1.2.

## why friction occurs

Friction occurs because no surface is perfectly smooth. Even surfaces that look smooth to the unaided eye make look rough or bumpy when viewed under a microscope. Look at the metal surfaces in the Figure 1.3. The aluminum foil These photos show two ways that friction is useful These photos show two ways that friction can cause problems is so smooth that its shiny. However, when highly magnified, the surface of metal appears to be very bumpy. All those mountains and valleys catch and grab the mountains and valleys of any other surface that contacts the metal. This creates friction.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

only rough surfaces have friction between them.

``````a. true

-->  b. false
``````

factors that affect friction between two surface include the

``````a) smoothness of the two surfaces.

b) area of the two surfaces.

c) amount of force pressing the two surfaces together.

-->  d) all of the above
``````

heavier objects have less friction with the floor than lighter objects.

``````a. true

-->  b. false
``````

``````a) exert less force on the ice.

b) make you weigh less on the ice.

-->  c) have less surface area in contact with the ice.

d) none of the above
``````

friction produces heat because it causes molecules to move faster and have more energy.

``````-->  a. true

b. false
``````

engine oil reduces friction between the moving parts in a car engine by

``````a) cooling the engine.

b) reducing the forces on the parts.

-->  c) making the parts slippery.

d) two of the above
``````

## diagram questions

No diagram questions associated with this lesson