This activity is done in three steps.
1) Students release steel marbles at different heights of the slide. They note that if the starting point is higher, the marbles travel further. This indicates that gravity produces kinetic energy.
2) They take glass marbles (usually three) bound by adhesive putty. This system represents a molecule or an atomic nucleus.
3) Starting from the bottom of the slide they reach the minimum height sufficient to separate the marbles when the system is released.
Take plastic tubes and cut it into three pieces of length ~70 cm. Two supporting parts of the main body of the tube are glued with hot glue at an angle of 90 degrees, to make a frame. The final part sits on this structure to make a slide (Figure 1).
Hypothesis: “Energy cannot be created or destroyed, it can only be changed from one form to another.”
Explanation: There are several forms of energy. Kinetic energy is related to the velocity of a body. But if I brake a car, where does this energy go? Into heat! You can measure the temperature of the brakes after stopping. Simply rub your hands and you will convert kinetic energy into heat.
Students release steel marbles at different heights on the slide and measure the distance where they stop. The teacher should ask what happened and why. The first observation is that the higher the starting point is on the slide, the further the distance travelled by the marble before it stops.
1) Gravity gives kinetic energy to each marble (more rigorously, transformation from potential to kinetic energy)
2) Friction stops the marble (and the energy is transformed into heat)
Hypothesis: “Objects are bound together and we need energy to break them.”
Explanation: What happens when we drop an object (say an egg) from a height of 1 cm or 1 meter? In the first case, some damage is observed on the egg’s surface, while in the second case the egg is destroyed. So, where did the kinetic energy of the egg go? Into breaking the egg. We need a certain amount of energy to break objects, called the “binding energy”.
Form a clump of glass marbles using a very small amount of adhesive putty (Figure 2). This represents a molecule, an atomic nucleus or more generally a “system”.
What is the mechanism to break the bond? The bond system needs a certain amount energy to be broken, if the energy is too low, nothing happens.
Keep the glass marble system at the end of the slide and then release the system (figure 3). Progressively increase the height (figure 4) until the energy is enough to separate the balls (see https://www.youtube.com/watch?v=7CHrKoGuZqQ).
Try various types of collisions (head-on, off-centred) with more than three marbles.
Explain what happens. Why do the marbles separate in some cases?
In some cases, the binding of the marbles is so strong, that it needs to be released from a higher point, possibly taking too much space in the classroom. Alternatively, another source of energy can be used to break the bound. One possibility is to push the marble with magnets.
What did we learn?
- Energy transforms
- Scientists use collisions to explore what the matter is made of.