Fig. 3 shows very magnified pictures of two surfaces in contact. In the first (A), a shoe is resting on the ground. The surfaces of the shoe and the ground can slide over each other relatively easily. In the second image (B) the shoe is being pushed down onto the ground. This makes the grooves on the surfaces lock into each other more making it more difficult to slide. In the third image (C) the shoe has many more deep grooves on its sole. This also makes the surfaces lock together more, and movement is difficult. Friction can be reduced by using a lubricant to fill the gaps in the grooves on the surfaces, making them smoother as shown in Fig. 4 below.
Fig. 4 A lubricant reduces friction by filling the gaps in the grooves of the two surfaces.
Fig. 5 Engine oil lubricates parts of the engine to reduce friction and wear and tear.
There is also some friction between surfaces in contact with liquids and gases, however. For example when a space shuttle returns to Earth there is a lot of friction between the shuttle and the gases in the atmosphere. This force of friction slows the space shuttle down.
Fig. 6 The surface of snow tyres, which may be used in winter, increases friction and therefore gives a better grip on icy roads.
Advantages of friction
1. Allows a good grip between car tyres and road.
2. Brakes in a car use friction to stop. 3. Warms hands when they are rubbed together.
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Fig. 7 A meteor burns up as it passes through the earth’s atmosphere. This is due to friction between the meteor and the gases in the atmosphere, converting motion energy to heat energy.
Disadvantages of friction
1. Causes moving parts in an engine to wear away.
2. Causes burns when climbing ropes. 3. Friction with the air slows down vehicles reducing fuel efficiency.
