Simple Machines and Their Functions

2. Many machines operate by multiplying the input force, thus increasing the output force. The amount that this force is increased is called the machine’s mechanical advantage. MA = output force **When the resulting force is greater than 1, a machine is said to have a mechanical advantage. input force Other machines work by only changing the direction, not the strength of the force while yet still others decrease force while increasing distance at the same time. CONFUSED? Let’s take a look at a few examples.......

3. LEVERS A lever has the ability to translate a small movement into a large movement (decrease in force) or a large movement into a small movement (increase in force) using a fulcrum, or pivot point A 1st class lever has the fulcrum in between the load (output force) and the input force. This changes the direction of force. The closer the fulcrum is to the load, the greater the mechanical advantage is. A 2nd class lever has the load in between the fulcrum and the input force. This does not change the direction of force. The closer the fulcrum is to the load, the greater the mechanical advantage. A 3rd class lever places the input force in between the fulcrum and the load. Unlike the other 2 levers, this provides no (<1) mechanical advantage, but increases the distance of the force. Direction is not changed.

4. PULLEYS Like levers, Pulleys either change the direction of force, or magnify the input force to make lifting easier. Increasing force requires increasing the distance the input force is applied. A single fixed pulley simply changes the direction of the force. Pull down, and the load goes up. With a MA of exactly 1, it does not increase the force applied. A single movable pulley doesn’t change the direction of force, but magnifies the force applied. With a MA of 2, it makes lifting easier, but you have input twice the distance! A combination of fixed and movable pulleys called a compound pulley, or block and tackle, changes direction and increases force. But force must be applied over a much greater distance to take advantage of the high mechanical advantage.

5. A wheel and axle can either magnify the distance of force while decreasing it, or magnify force while decreasing distance. You would have to turn the axle with a lot of force to move the wheel once around. But your 1 inch spin applied to the axle would translate a 24 inch spin in the wheel. Likewise, turning the wheel instead would be far easier but the a 24 inch movement applied to the wheel would only result in a 1 inch rotation at the axle. 24” 1” If its greater distance you are after, apply your force to the axle. If its greater force you want, apply your force to the wheel. Either way, the same amount of work is done! An Inclined Plane or Ramp works the same way. You can apply a lot less force if you are willing to travel a greater distance! In the end, however, the same amount of work is done.

6. A wedge takes input force and focuses it over a smaller area. Because it is essentially two inclined planes back to back, it acts to force apart as it is pushed into a material. The force applied here is directed into the edge. When a force is focused over a smaller distance, it has a greater impact. Who will have an easier time entering the water? Using this same concept, how is this man able to lay down on a bed of sharp nails without hurting himself?

7. Think of a screw as a inclined plane wrapped around a cylinder. But....With a inclined plane, we move the object over the distance. With a screw, however, we move the inclined plane, which in turn, moves the object! Most of us use “screws” to secure 2 objects together. In this task, a wood screw will use yet another simple machine in itself. Which one??

8. A compound machine is a combination of several simple machines working together to carry out a specific function. What simple machines does a modern fishing pole incorporate?