Chapter 8 Machines
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Friction helps us in many ways. Without friction, cars would skid off
the road and nails would pop out of walls. Friction also enables us to
walk on most surfaces without sliding. But it can also slow us down and
produce unwanted heat. When you pedal your bicycle, you are working
against friction.
The moving parts of mechanisms do not have perfectly smooth
surfaces. The tiny projections on the surfaces rub on one another. This
creates friction and results in heat. The friction between the moving parts
must be minimized so that:
• Less energy will be needed to work the machine
• Wear and tear will be reduced
• Moving parts will stay cooler
Motion Application Symbol
Linear
Rotary
Reciprocating
Oscillating Os Os ci ci ll ll at at in in g g g g
gure 8-58. Mechanisms are used
to create different kinds of motion.