Explain how lubricating the wheels of the skateboard can increase the speed of the girl

Less friction to stop the wheel from turning

When oil, grease or graphite is applied

between the moving part of a machine,

a thin layer is formed there and moving

surfaces do not directly rub against each

other (Fig. 12.13). Interlocking of

irregularities is avoided to a great extent.

Movement becomes smooth. The

substances which reduce friction are

called lubricants.