Magic with Newton

Basic concepts

Physics	Forces	Gravity	Weight

The following is an introduction:

Every day we experience in nature all kinds of forces, movements, accelerations. But a lot of times we're not aware and we don't realize how they work. In this experiment we're going to test the basic operation of forces with this curious balance.

Scientific basis

The experiment is based on the balance of forces postulated by Newton. The bottle will remain balanced at the edge of the table thanks to the fact that we will compensate for the downward vertical force with another upward vertical. In this way Newton's first law is fulfilled which says that a body is in equilibrium always and count the sum of all forces acting on it as zero.

Materials

• A bottle full of water
• Three flat wooden sticks
• A rope or cord
• A balance surface, in my case the edge of a table
• A weight to hold the system in the intermediate step

Preparation

First we're going to prepare the system

1. We put on our safety glasses
2. We tie the cord to the bottle cap
3. We weigh the first stick, about a third of it protruding from the edge of the table
4. We hang the cord tied to the bottle of the stick

The procedure

Now we start with the real part of the experiment, where we create the balance of forces

1. We place the second stick in a horizontal position so that it is held between the two ends of the cord. We need to place it on a small of the first stick.
2. We place the third tensioned stick between the tip of the first stick sticking out from the table and the middle point of the second horizontal stick. This step is the most complicated, so we can keep testing and adjusting the second stick until we get them to hold themselves.
3. Make a prediction! Will it hold only if we remove the weight that secures everything?
4. Now we can remove the weight that held the first stick slowly and see that the system is balanced without the help of external forces.

Observation and results

As you can see, the system is balanced at the edge of the table with no help other than the three chopsticks used. Logic tells us that this should not be the case since there is nothing to hold the first stick to the table and nothing to hold the bottle from below. But what we've achieved by adding the other two sticks is to re-conduct the force, also called the strain that passes through the cord by the weight of the bottle. This voltage was vertically descending in principle. By adding the horizontal stick we trickle some of the force into this plane and finally by adding the last stick we are able to return this tension that we have deflected from the cord to the first stick. In this way we have managed to apply an equivalent force on the stick, we could say we have counterbalanced the weight of the bottle with the sticks.

Pick it up!

Make sure you leave everything clean and tidy once you're done with the experiment. You can flush the water (with or without dye) down the drain and put the bottles in the container. Put back the tools and other utensils you need.

Adult supervision and safety first

• Follow the experiment instructions carefully.
• It is advisable for an adult to supervise the performance of the test, assisting in the use of potentially dangerous materials or utensils if not used correctly.
• Similarly, an adult must determine whether the experiment to be performed is appropriate for the age of the pupil taking part in the activity.
• Doing science experiments at home is a fun way to learn the practical part of science, but it may require taking extra precautions and/or cluttering or dirtying the work area.