Centrifugal Force

The inertial force (Fin) comes from the inertial system. Inertial system is a system that performs a rotation movement with constant angular speed and constant acceleration. The inertial force (Fin) exhibits adverse direction from the rotation system, if it goes from the center of rotation to a circular path. The observer can feel this force only if he/she is standing in the rotation system. This force is called the centrifugal force (Fin = Fcf).

Fcf = mv2/R = 4p2mR/T2 = mv2R

From the formula we can see that the strength of the centrifugal force comes from the mass of the body m, the distance between the body from the center of the circular movement R and the period T that comes from the center of the circular movement R and the period T that comes from the angular speed w.

For a better understanding of centrifugal force we will make a conduct a simple experiment:


Instructional goal:

To demonstrate centrifugal force.

National standards (9-12) addressed

National standards (5-8) addressed

Step 1.
Make a hole in the exact center of the bottom of one bottle. Ease off the bottle-top. If there is a stopper, cut it off. Select a rubber band that is about two-thirds as long as the bottle. Use the matchstick to push the rubber band through the bottle, loop its end around the matchstick. Tape the matchstick to the bottom of the bottle. Cut a piece of wire about one-and-a-half times the length of the bottle, and bend one end of it into a hook. Pass the hook through the bottles neck and catch the bands loose end.

That way you will get the power wire that will be mentioned later.
Picture 1.

Step 2.
Cut an arm out of thick cardboard to the size shown previous. Punch a hole in its exact center. Glue two balsa wood blocks to the two ends of the cardboard arm. Make a small hole through the center of each block.

Step 3.
Unbend the power wire, and poke it through the arm. Bend it down and tape it firmly to the arm. Wind the arm up a few turns to test that it rotates freely.

Step 4.
Cut the bottoms off two empty plastic bottles � transparent ones if possible.
Punch two small holes in them. Cut two lengths of wire, about one-and-a-half times the width of the tubs.

Step 5.
To fasten the tubs to the balsa wood blocks, thread the wires through the holes.
Then twist the ends over the rims of the tubs. Check that the tubs can swing freely.

Picture 2

Step 6.
Testing time! Wind the arm up. Then press a finger over its center to serve as a brake. Keeping a firm hold on the base, ease your finger off. The arm should gain speed gently. Wind up about 50 turns.

Step 7.
Cut a slider out of postcard to fit the dimensions of the arm. Bend the edges over. Wind the arm up, and put the slider on its exact center. Let the arm spin. The slider will stay in place. But if you put the slider just a little off center it will move away from the center hole. This outward momentum is called centrifugal force.

Step 8
Try the same trick, but this time with water. Fill the two tubs about half full. Make sure there are no leaks. Take care that the arm speeds up at a steady rate. See what will happen with the water.

Author: Vladimir Simonovski

Curator: Al Globus
NASA Responsible Official: Dr. Ruth Globus
If you find any errors on this page contact Al Globus.
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