 Mechanical Advantage Let's examine how to apply lever ratios to calculate the mechanical advantage in basic mechanisms. Every time you open a door, you are using a Class II lever to multiply force. This multiplication of force is called mechanical advantage. The formula used to calculate mechanical advantage is F2, the output force, divided by F1, the input force. The nutcracker is another example of using a Class II lever to multiply force. You can calculate this multiplication of force by substituting the values of F1 and F2 into the mechanical advantage formula. But before doing this, you must determine the values of F1 and F2 using the lever ratios. Where F1 equals input force, F2 equals output force, L1 equals input length, L2 equals output length, S1 equals input displacement, and S2 equals output displacement. Mechanical advantage, or MA, equals F2 over F1. Given L1 equals 4.5 inches, L2 equals 1.5 inches, and F1 equals 5 pounds, we calculate F2 by cross-multiplying. In this example, F2 equals 15 pounds. You can now calculate mechanical advantage by dividing F2 by F1. 15 pounds divided by 5 pounds equals 3. In this example, a Class II lever was used to multiply the 5 pound input force by 3 to exert a 15 pound force on the nut or output force. Here the mechanical advantage equals 3. Let's do a quick review before we move on. Mechanical advantage equals F2 divided by F1, which equals the output force divided by the input force. In this example, applyers, which is a Class I lever, is used to multiply force. The procedure to calculate mechanical advantage in a Class I lever is the same as shown previously with the Class II lever. Given the information above, use the lever ratios and the mechanical advantage formula to calculate mechanical advantage. Given L1 equals 5 inches, L2 equals 2 inches, and F2 equals 50 pounds, we calculate F1 by cross-multiplying. Here F1 equals 20 pounds. The mechanical advantage equals F2 divided by F1. So here the mechanical advantage is 50 pounds divided by 20 pounds, so the mechanical advantage equals 2.5. Applying lever calculations to rotational devices. Besides making it easier to grip, the handle on a screwdriver also multiplies the force exerted when turning a screw. The picture to the left shows the inside of a drill that is being used as a powered screwdriver. The shaft inside the screwdriver serves the same purpose as the handle on the manual screwdriver. The fulcrum of the lever is centered on the handle, on the shaft and on the flathead screwdriver piece. If the force exerted by the shaft is 15 pounds, calculate the force at the tip of the screwdriver and the mechanical advantage. We know F1 equals 15 pounds, L1 equals 0.3125 inches, and L2 equals 0.09375 inches. We can calculate F2 by cross-multiplying. The mechanical advantage equals 50 pounds divided by 15 pounds, so here the mechanical advantage is 3.3. Congratulations! You have completed this learning activity on mechanical advantage.