1. Simple Machines ~ Levers ~

2. Simple Machines Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

3. What is a machine? A machine is a device that makes work easier by changing the size or direction of a force. There are SIX types of simple machines Levers, inclined planes, wheel and axle, wedges, pulleys, and screws Complex machines (like a car) are made up of several simple machines put together.

4. Amount of Work • A machine makes work easier….but remember that is doesn’t take the amount of work away, it changes the way in which you do the work leaving the amount the same. **You change the directionor distance • Input Force – the work you do on the machine….”effort” • Output Force – what is trying to overcome the “resistance”……”Load”

5. Mechanical Advantage • The number of times a force exerted on a machine is multiplied by the machine • Finding the ratio of output force to input force gives you the mechanical advantage of a machine. M.A. = output force input force • The efficiency of a machine is just the percentage of the above formula

6. Mechanical Advantage • Mechanical advantage is the ratio of output force divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one. • If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10. • In machines that increase distance instead of force, the MA is the ratio of the output distance and input distance. • MA = output/input

7. Levers • Made up a bar that pivots, or rotates, at a fixed point called a fulcrum. • The force applied is called the effort and the object being moved is the load, sometimes called the resistance. • Levers make work easier in three ways, giving up three groups of levers

8. The 3 Classes of Levers • The class of a lever is determined by the location of the effort force and the load relative to the fulcrum.

9. To find the MA of a lever, divide the output force by the input force, or divide the length of the resistance arm by the length of the effort arm.

10. First Class Levers • The fulcrum is located between the effort and the load • Example: seesaw, scissors

11. Fulcrum is between EF (effort) and RF (load)Effort moves farther than Resistance.Multiplies EF and changes its direction

12. Second Class Lever • The load is located between the fulcrum and the effort • Example: nutcracker, wheelbarrow

13. RF (load) is between fulcrum and EF Effort moves farther than Resistance.Multiplies EF, but does not change its direction

14. Third Class Lever • The effort is applied between the fulcrum and the load. Example: a fishing pole, a hammer, broom, and a baseball bat

15. EF is between fulcrum and RF (load) Does not multiply force Resistance moves farther than Effort.Multiplies the distance the effort force travels

16. Levers in our Body • What class of lever is our hip?

17. Levers in our Body • What class of lever is our elbow and arm?

18. Levers in our Body • What class of lever is out leg?

19. BrainPop video on Levers • http://www.brainpop.com/technology/simplemachines/lever/