2. Simple Machine Each one makes work easier to do by providing some trade-off between the force applied and the distance over which the force is applied. That is, a simple machine changes the magnitude or direction of the force.

3. Levers Examples: Hammer, Crow Bar, Bottle Opener, Scissors, pliers, fingernail clippers, wheelbarrow A lever is a stiff rod that rotates around a pivot point. Downward motion at one end results in upward motion at the other end. Depending on where the pivot point is located, a lever can multiply either the force applied or the distance over which the force is applied.

4. Inclined Plane

5. Wheel and Axle In this machine a wheel or spoke is locked to a central axle so that when one is turned the other must turn. A longer motion at the edge of the wheel is converted to a shorter more powerful motion at the axle. In reverse, a short powerful force at the axle will move the wheel's edge a greater distance.

6. Screw Jar lid, light bulb, stool, key ring A screw is a central core with a thread or groove wrapped around it to form a helix. While turning, a screw converts a rotary motion into a forward or backward motion.

7. Wedge Chisel, nail, fork, ax, knife A wedge converts motion in one direction into a splitting motion that acts at right angles to the blade. Nearly all cutting machines use the wedge. A lifting machine may use a wedge to get under a load.

8. Pulley A single pulley simply reverses the direction of a force. When two or more pulleys are connected together, they permit a heavy load to be lifted with less force. The trade-off is that the end of the rope must move a greater distance than the load.

9. Output Work of a machine can never be greater than input work. Simple machines don’t “amplify” the amount of work. Mechanical Advantage: the resistance force (the force exerted by the machine) divided by the effort force (the force exerted by the person on the machine) MA = F r ÷ F e. If F e = F r, then MA = 1.

10. Ideal Mechanical Advantage, IMA = d e ÷d r, or displacement of effort (your) force divided by the resistance (machine’s) force. Efficiency of a machine = (W o /W i ) x 100 = (MA/IMA) x 100

11. Practice Problem Using a 90.0% efficient lever, what input work is required to lift an 18.0-kg mass through a distance of 0.50m?