The Screw and Conservation of Energy

1. The Screw and Conservation of Energy

2. Activity • Materials:Nine inch paper square, pencil, tape, marker, tabletop • Procedure:Cut the square in half to make a right triangle.  Use the marker to outline the diagonal side of the triangle.  Now place the paper face down on the table.  Place the pencil on one of the short sides of the triangle.  Wrap the pencil around the triangle.  Use the tape to keep it in place. • Things to think about during the experiment:-What simple machine is the right triangle?-What simple machine was created when you wrapped the pencil around the triangle?-Name some examples of this machine. • Conclusion:You made a screw out of an inclined plane when you wrapped the triangle around the pencil.

3. Simple machines • Simple machines are "simple" because most have only one moving part. • Some are so simple, they don't have any moving parts! • When you put simple machines together, you get a complex machine, like a lawn mower, a car, even an electric nose hair trimmer!

4. Simple machines • A machine is a device that helps make work easier to perform. • (Remember, Work = Force X Distance). • A machine makes work easier to perform by accomplishing one or more of the following functions: • changing the direction of a force, • increasing the magnitude of a force, or • increasing the distance or speed of a force.

5. CONSERVATION OF ENERGY • No machine can increase both the magnitude and the distance of a force at the same time. • When a machine produces an increase in force, there is always a proportional decrease in the distance moved • Conversely, when a machine produces an increase in distance, there will be a proportional decrease in force.

6. CONSERVATION OF ENERGY • Another way to state this concept is that no machine can produce more work than the amount of work that is put into the machine. • In fact, if you ignore the work lost due to friction and its inefficiencies, the amount of work produced by a machine is always exactly the same as the amount of work put into the machine. • This is known as the Law of Conservation of Energy.

7. CONSERVATION OF ENERGY • This concept can also be put into the form of an equation. (Remember that work is equal to force times distance.) • F1 X D1 = F2 X D2 where, F1 = Input Force F2 = Output Force • D1 = Input Distance D2 = Output Distance

8. CONSERVATION OF ENERGY • As an example, assume that it requires 50 Nof input force in the handle of an automobile jack in order to raise a 500 Nweight a distance of one meter. What distance must the jack handle be moved in order to accomplish this task? The answer can be calculated as follows: F1 X D1 = F2 X D2

9. CONSERVATION OF ENERGY • Remember, a machine is any device that makes work easier • In science, "work" means making something move.

10. The Screw • The screw is really an inclined plane in the round with a wedge at the tip. • The wedge is the pointed end. • The inclined plane is the thread that wraps around the screw. • While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp • Screws are used in many different places to hold things together or to move things up and down

11. The Screw • Basically, a screw is like the ramp • and the width of the thread is like the angle of an inclined plane. • The vertical distance between two adjacent screw threads is called the pitch of a screw. The wider the thread of a screw, the harder it is to turn it. • And here's the trade-off: If you've ever had to put in a screw with really narrow threads, you've probably found that you have to turn it a really long time to get it to go anywhere. • Just like in a ramp, the easier the effort, the longer the distance you have to move something

12. The Screw • One complete revolution of the screw will move it into an object a distance to the pitch of the screw. The pitch of any screw can be calculated as follows: