(iii) The friction between two surfaces decreases with the increase in the weight of a body. (iv) Tho friction offered by the wheels is called sliding friction.
Answers
Answer:
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 below
Friction between the graphite in a pencil and a sheet of paper leaves a mark on the paper.
Friction between a bicycle brake pad and the rim of a wheel causes the wheel to stop turning.
Did you ever rub your hands together to warm them up, Why does this make your hands warmer? The answer is friction.
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 below. The aluminum foil is so smooth that it's 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.
Factors that Affect Friction
Rougher surfaces have more friction between them than smoother surfaces. That's why we put sand on icy sidewalks and roads. Increasing the area of surfaces that are touching also increases the friction between them. That's why you can't slide as far across ice with shoes as you can on the thin blades of skates. The greater surface area of the soles of the shoes cause more friction and slow you down.