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### Mechanical Principles

When you use a machine, even your fingers, you can see two forces at work: the applied force, called effort (E), and the resisting force, called resistance (R).

As an exercise, lay your pencil on your desk, and then pick it up using your forefinger and thumb. Watch your hand and arm carefully as you slowly reach down, squeeze the pencil, and pick it up. You have just witnessed several physical and mechanical principles at work: gravity, Newton's first law of motion, conservation of energy, and lever action with a mechanical advantage. In this case, the pencil was the resistance force, and your fingers and arm were the effort force.

In many cases, machines help you to use more force than simple strength will allow; this is ...

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