Momentum and Energy


What are examples of levers?

The first-class lever shown above has a mechanical advantage greater than one. How could you arrange the location of the pivot to make the mechanical advantage less than one? Look closely at a pair of scissors. Note that you can adjust the mechanical advantage by moving the region of the scissors you are using to cut. Where would you put the material to be cut if more force is needed to make the cut? You would put it, nearer the pivot. On the other hand, if the material is easily cut, cutting near the tip of the blades provides enough force and speeds up the cutting. What class lever is a can or bottle opener? Locate the pivot point and compare to the three drawings above.

Your forearm is a lever, with the elbow joint being the pivot. Where does the bicep muscle attach? The attachment is close to the elbow, so the forearm is a third-class lever. Are other muscles and bones in your body so easily characterized? Most are not because tendons that transmit the force from the muscle to the bone are long and go through several bends.

Consider sports equipment like baseball bats, tennis racquets, and golf clubs. They are often used as extensions of your arms, so the person plus the bat or club has to be examined together. But note that in every case the system is a third-class lever, where a large distance moved (and therefore greater speed) is favored over an increased force.


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