Multiple choice

If oils or other liquid lubricants cannot be used to reduce friction in a machine, then which of the following statements is TRUE?

  1. An air cushion between the moving parts is used to reduce friction.

  2. Gun powder is sprinkled between the moving parts of a machine.

  3. The moving parts of the machines are made rough.

  4. Both (1) and (3).
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A Correct answer
Explanation

In some machines, it may not be advisable to use oil as lubricant. In such cases, an air cushion between the moving parts is used to reduce friction.

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