The Spoon and Ruler Experiment

Friday, September 19, 2008

The Spoon and Ruler Experiment

Spoon and Ruler

This is a normal experiment which gives wierd results.

What you need?

A spoon : Better be a plastic one. You need to cut out the handle. We need only the head part, which is going to act as the base of the apparatus.

A ruler : Better be 30cm ruler. It can be of any material.

Some clay : For using as a glue and for the balancing act.

The procedure

1. Take the spoon.
2. Cut out the handle (if you haven't done it yet). It looks like a bowl, but not symmetric.
3. Take some clay.
4. Mix it with some water to make it into sticky paste.
5. Place some of that to fill the spoon bowl and add a little more clay on top.
6. Take the ruler.
7. Place it horizontally on top of the clay. The ruler must be placed at the middle, ie. same length in both directions.
8. The clay acts as the glue and the spoon and ruler becomes one body.
9. Because of the asymmetry of the spoon, the ruler will not be balanced on the spoon.
10. Make two spheres out of the clay paste.
11. Place these spheres on either end of the ruler to make it balanced.
12. Now the only surface touching the ground is the underside of the spoon.
13. The apparatus is complete.
14. Now onto the main event.
15. Rotate the apparatus like a fan. Rotate in both directions. What do you see ?

What I see ?

1. When the ruler is rotated on the spoon, in one direction (in our case clockwise), the ruler rotates smoothly without a jerks. And stops after sometime.
2. When rotated in the opposite direction (anti-clockwise in our case), the rotation is jerky, sometimes the ends touch the ground. Before stopping, it rotates once or twice in the opposite direction and comes to a halt.

Yeah, this is what happens... WHY ?

I haven't done it myself :D My friend did...

Some variations we tried...

1. The shape of the clay balls are irrelevant
2. When the rotation is too slow, there is almost same effect. But, as the spped increases the difference becomes visible.
3. Whether the balancing is done by placing two balls of different masses at same distances from the centre OR by same mass at different distances from the center, doesn't have an effect.

What we haven't tried?

1. Haven't tried with other material than clay.

Some hypotheses:

1. The magnetic content in the clay interacts with the earth magnetic field
2. The rotation of the earth
3. Attraction of sun, moon, other planets...
4. Difference in the way we rotate, as it is done using hand
5. The gyroscopic effect. See more about Gyroscope...

So, what is your findings? Is it always smooth in the clockwise direction?


Found the solution from an expert...

The spoon and the ruler combination (without the clay balls) is an asymmetric object. So, when it is rotated, it will behave differently in different directions.

When we balanced it by placing the clay balls, it is a slow process and for static only. But rotating involves movement and much more force. So, the balancing doesn't have any effect on the way of its rotation. When it is the spoon and ruler only, the difference in rotation is due to the asymmetry of the spoon. When we use the clay balls, the asymmetry is by the difference in weight of the clay balls on either side (or the distance if same weights).

The system can be modified using trial and error to rotate same in both directions, by varying the weights of the clay balls. But, after it is done, the ruler will not be balanced anymore.

As suggested by Anonymous as comment, it is similar to a Rattleback.

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Anonymous said...

My algebra teacher in high school had a piece of similarly shaped plastic which exhibited similar properties.

I think there is a name for this geometric shape that, when spun in one direction, it will slow down and then spin in the opposite for a few turns.
Nothing to do with magnetics AFAIK

Here it is..

Cool that you found a way to make one at home though!

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