1. Simple Machines and Work

2. What is a Simple Machine?  A simple machine has few or no moving parts.  Simple machines make “work” easier

3. Wheels and Axles  The wheel and axle are a simple machine  The axle is a rod that goes through the wheel which allows the wheel to turn  Gears are a form of wheels and axles

4. Pulleys  Pulley are wheels and axles with a groove around the outside  A pulley needs a rope, chain or belt around the groove to make it do work

5. Inclined Planes  An inclined plane is a flat surface that is higher on one end  Inclined planes make the work of moving things easier

6. Wedges  Two inclined planes joined back to back.  Wedges are used to split things.

7. Screws  A screw is an inclined plane wrapped around a shaft or cylinder.  The inclined plane allows the screw to move itself when rotated.

8. Levers  A lever is a simple machine containing a bar that can turn around a fixed point  Fixed point is called a fulcrum  There are three classes of levers

9. Levers  The force the person applies to the machine is called effort force  The object to be lifted, the load, is called the resistance.  The force the machine uses to move the resistance is called the resistance force  The force the machine exerts is greater than the force the person exerts, SO using a machine makes a person’s job easier!

10. Levers-First Class  In a first class lever the fulcrum is in the middle and the load and effort is on either side  Think of a see-saw

11. Levers-Second Class  In a second class lever the fulcrum is at the end, with the load in the middle  Think of a wheelbarrow

12. Levers-Third Class  In a third class lever the fulcrum is again at the end, but the effort is in the middle  Think of a pair of tweezers

13. Simple Machines and Work  Energy cannot be created or destroyed; and, because energy is the ability to do work, work cannot be created either  No simple machine can do more work than the person using it supplies  Machines can increase or change the direction of the force a person exerts; and, some machines allow a person to use less force to do the same amount of work

14. Simple Machines and Work  The amount of work a person puts into a machine is called the work input  Work input equals the person’s effort force multiplied by the distance of that effort work input = fe × de  The amount of work actually done by the machine against the resistance is called the work output  Work output equals the resistance force multiplied by the distance the resistance moved work output = fr × dr

15. Simple Machines and Work  Work output can never be greater than work input because energy cannot be created  The efficiency of a machine measures how much useful work it can do compared with how much work was put into it efficiency = work output/work input × 100%  Efficiency is written as a percent, and multiplying by 100 tells you what percent of the work input is converted to work output  ALL machines have efficiencies that are less than 100 percent

16. Mechanical Advantage  A simple machine makes a task easier because it multiplies the force a person applies  The number of times a machine multiples your effort force is called the mechanical advantage  mechanical advantage = resistance force /effort force

17. Mechanical Advantage  Suppose a machine lifts a resistance that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage?  MA = Fr/Fe MA = 30 newtons/10 newtons MA = 3

18. Mechanical Advantage  Suppose a machine lifts a resistance that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage?  MA = Fr/Fe MA = 30 newtons/10 newtons MA = 3

19. Mechanical Advantage  Suppose a machine lifts a resistance that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage?  MA = Fr/Fe MA = 30 newtons/10 newtons MA = 3

20. Mechanical Advantage  Suppose a machine lifts a resistance that weighs 30 newtons when a person applies an effort force of only 10 newtons. What is the person’s mechanical advantage?  MA = Fr/Fe MA = 30 newtons/10 newtons MA = 3

21. Mechanical Advantage  You can increase the mechanical advantage of a lever simply by moving the fulcrum closer to the resistance and farther from the effort force  The effort arm is the distance between the fulcrum and the effort force of a lever  The resistance arm is the distance between the fulcrum and the resistance force of a lever MA = effort arm/resistance arm

22. Mechanical Advantage  To increase Mechanical Advantage in a pulley, simply add more pulleys  For each pulley the MA is 1