Thursday, May 24, 2012

Science Lab - Force and Circular Motion

8th Grade - Physical Science

A. Purpose: The purpose of this experiment is to demonstrate the properties of circular motion and the force that upholds it. The force required for circular motion to occur properly is a special force called centripetal force. An example of centripetal force will be performed in the following experiment, which is very helpful for any experimenter in order to produce a true understanding of the unique and complex force regarding circular motion. Centripetal force is a hard concept to grasp, but evaluating the reasons and results will certainly be of great assistance.

Centripetal force is basically defined as the force necessary to make an object move in a circle. It is always directed perpendicular to the velocity of the object. This means that the force always points toward the center of the circle. One example of centripetal force is a loop on a roller-coaster. In this case, the track applies a centripetal force on the cars. The cars initial velocity is traveling forward, but the track is applying the force, the centripetal force, on the cars, which causes the cars to begin traveling in a circle. Yet another example is in the solar system. Earth for example is traveling through space at thousands of mile per hour. The gravitational force of the sun however causes the earth to bend its initial velocity. The sun's gravitational force acts as the centripetal force in this case. Sir Isaac Newton explained centripetal force in this statement, “A centripetal force is that by which bodies are drawn or impelled, or in any way tend, towards a point as to a centre.” (Wikipedia)

Centripetal force was first put into mathematical definition by Dutch scientist Christiaan Huygens. Although his formula for centripetal force is extremely complex, three basic laws of centripetal force have been accumulated over time. They are:
1. Circular motion requires centripetal force.
2. The larger the centripetal force, the faster an object travels in a circle of a given size.
3. At a given speed, the larger the centripetal force, the smaller the circle.
These are the three laws that have helped many grasp the concept of centripetal fore itself.

Centripetal force is often mistaken for centrifugal force. Centrifugal force at times seems rational, but is actually a fake. Centrifuge is the Latin word for “center fleeting” ( While many believe that centrifugal force is the reason mud spins off tires, or passengers lean to one side in a car turning a curve, those are really just results of Newton's first law of motion, which states,”An object in motion (or at rest) tends to stay in motion (or at rest) until acted on by an outside force.” So then, the reason car passengers are thrust to one side during a curve is that their bodies are staying in motion until the physical car makes them turn with it.

This experiment hopes to show the reality of centripetal force. Circular motion will be explained in a manner as to easily be understood by the ordinary person. Also, centrifugal force shall leave one's mind as a simple myth, and not a fact. This experiment will show as well the benefits of centripetal force using easy, everyday materials.

This experiment is of interest to science because without centripetal force, there is no way earth could survive. Centripetal force is something unknowingly used everyday. If no one discovers the superior value of understanding this unique force, then man is left being content with seeming unintelligent.
Experiments such as this one are important so that the reality of centripetal force may be shown in easy ways.

Hypothesis: If every step is proceeded as necessary, and the washers are spun at the exact speed needed, then the goal of centripetal force being demonstrated will be successful.

B. Supplies:

1. A mechanical pen
2. A black marker
3. Thin string or thread
4. Five metal washers
5. Stopwatch
6. Scissors

C. Procedure:

1. Unscrew the bottom part of the casing from the pen and remove the insides from the pen.
2. Set everything aside except for the bottom part of the casing.
3. Thread about a foot of string through the casing. If you is having trouble getting the string all the way through, stick the string in the pointed side of the casing and suck on the other side with mouth. The suction will pull the string through. Tie one washer on the end that is on the pointed side of the casing and tie two washers on the other end.
4. Lay your device on the table and pull the string so that about 6 inches of string comes out of the pointed side of the casing. Next, use your marker to make a strong black mark all around the string, right where it comes out the other side of the casing. The mark needs to be easy to see.
5. Hold the device by grasping the pen. Make sure that the pointed end of the pen points up. Begin twirling the single washer on the end so that it moves in a circle.
6. Get used to how this thing operates. Notice that as you twirl the washer faster, the string pulls out the end, causing the circle that the washer sweeps out to become larger. If you slow the twirling down, the string goes the other way, making the circle smaller.
7. Adjust the rate you are twirling until the black mark you made is visible right at the bottom of the pen casing. This tells you that there are 6 inches of string extended from the point end of the casing. In other words, the radius of the circle swept out by the single washer is 6 inches.
8. Watch the washer as it moves in a circle. You are going to begin counting the number of full circles the washer makes. This can be a little tricky, so get used to the motion of the washer, keeping the black mark just at the bottom of the casing.
9. When you're ready, start the stopwatch and time how long it takes for the washer to make twenty full circles. Do this five times and average the result.
10. Next, tie two more washers to the end of the string that already had two washers on it. That way, there are now four washers on one end and one washer on the other. 11. Repeat steps (5-7) determining how long it takes the washer to make twenty full circles in this new configuration. 12. This step might be hard, but try to do it anyway. Try to twirl the washer so that the time it takes the washer to make twenty full circles equals equal to the time in step 7, when you had only two washers on the other end. In other words, if you are trying to twirl the washer with the same speed as in step 7.
This does not need to be done perfectly, just try to get reasonably close. 13. Notice where the black mark is when the washer twirls with the same speed as it had in step 7. 14. Finally, while the washer is still twirling around, cut the four washers off the string with the scissors. Make sure no one else is near when this is done. Also, make sure there are no breakables in the room. Note what happens. 15. Clean up the mess.

D. Observations:

1. Casing is removed cleanly and easily, inside of pen can be described as any other inside of a pen.
2. Everything is set aside with ease
3. String is threaded through the casing, although suction with the mouth was necessary. Two washers are tied on one side with a basic square knot, and one washer is tied on the other end using the same method.
4. Six inches of string are pulled from the pointed side of the casing. Sharpy brand black marker is used to mark. Mark is thin but bold.
5. Pen casing is held as directed. Top washer begins to spin fairly easily counter-clockwise.
6. Adjusting of spinning speed is attempted. Spinning begins to become more natural.
7. Black mark is visible at bottom of casing.
8. Washer is watched carefully. Preparing to count soon.
9. Iron Man brand stopwatch is started. Washer makes twenty full rounds and the watch is stopped. This is repeated four more times. Average time turns out to be just at 10 seconds.
10. Two more washers are tied onto the side with two washers already attached. Same square knot is used to tie the second two on. Four washers are now on one side of the string, and one remains on the other side.
11. Steps (5-7) are repeated, and average time taken for washers to make twenty full rounds comes to about 5. 27 seconds.
12. Step is extremely difficult, but closest attempt trying this came to a time of 9.86.
13. Black mark is well below pen casing.
14. Washers are cut with orange and gray scissors. Lone washer flies of in a straight line, nearly colliding with a television.
15. Mess is cleaned up in approximately 4 ½ minutes.

E. Conclusions:

This experiment was extremely successful in proving the existence of centripetal force. The above hypothesis was confirmed in demonstrating the effects of circular motion, and centripetal force. The washers made great example objects to show these effects. When two more washers were added to the bottom end of the casing, it demonstrated the second and third law of centripetal force very clearly and easily.

Honestly, there is no way that this experiment could possibly be improved. Besides the fact that the particular experimenter of this procedure could have made sure to stand a little farther back from the television, it was a perfect success. The usefulness of this experiment can be varied for many reasons of education and research. The washers could be substituted with any other reasonably small, heavy objects, or for larger scale operations, the general build could just be enlarged for official scientific research.

Ideas for future research are hard to generate when it comes to centripetal force, because scientists believe that research in this particular field has gone as far as possible. Of course, science has never gone as far as is can go. For man can never know when all facts have been discovered. Perhaps further research can be established throughout the process of constant discoveries made every day in the field of science.

F. Bibliography:

Joy Wagon,“Centrifugal Force, The False Force” Regents Prep
Document: /regents/physics/phys06/bcentrif/centrif.htm

Wikipedia contributors, “Centripetal Force,” Wikipedia, The Free Encyclopedia
Document: /wiki/Centripetal_force

Wile, Dr. Jay L. Exploring Creation with Physical Science, 2nd Edition. Apologia Educational Ministries, Inc. 2007

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