Teaching Activity planned by Irene Salmaso and Biagio Ambrosio during the PhD course “Designing innovative public engagement activities”, held at the University of Padua in 2024.

Short Description of the Activity

What does entropy mean, and how does it work? In this experience, through the use of colours and smells, it will be possible to perceive the different degrees of entropy which exist in more or less disorderly systems, in order to discover how it evolves with time.

Materials

  • Blue, red and yellow poster paints
  • 3 food flavourings/different recognizable essential oils (for example vanilla, almond, lemon)
  • Paintbrushes
  • Plastic cups, teaspoons and saucers
  • Paper sheets (circa 20)
  • Paper towel
  • Clothespins, twine and scotch for hanging the sheets
  • Printout of a spiral galaxy (link for download)
  • 6 balloons
  • 6 cardboard boxes
  • Scissors
  • 1 needle

Preparing the activity

1. Associate a colour to each smell (for example blue-vanilla, red-almond, yellow-lemon) and cover each vial with paper of the associate colour.

2. Prepare 10 ten sheets, colored on one side in the following way:

    • 1 white sheet, without colors
    • 1 sheet painted yellow
    • 1 sheet painted blue
    • 1 sheet painted red
    • 1 sheet painted yellow; once dry, add a red layer, so that you cannot see the yellow
    • 1 sheet painted yellow; once dry, add a blue layer, so that you cannot see the yellow underneath
    • 1 sheet painted green, obtained by the mix of dall’unione di blue and yellow
    • 1 sheet painted orange, obtained by the mix of red and yellow
    • 1 sheet painted violet, obtained by the mix of blue and red
    • 1 sheet painted brown, obtained by the mix of red, blue and yellow.

3. Hang the colored sheets with pins on the string, so that the white side facing the group of participants. Spray on this side the aromas associated to the colors used (do not spray anything on the white sheet).

4. Mix some poster paint in the plastic cups with the related perfume, according to the association chosen in point 1 (for example blue-vanilla, red-almond, yellow-lemon). The number of aroma drops to be added depends on their intensity, which may vary according to type and brand. In any case, we suggest 4-8 drops for a quarter of a glass.
The mixture must be continuously stirred to prevent it from separating and drying. Moreover, not to waste color, we recommend you give participants a small amount as needed, by using plastic teaspoons (one for each color to avoid contamination).

5. Prepare a drawing of a spiral galaxy, where red represents dust, yellow represents stars and blue represents gas. It must be similar in shape and size to the one of the one in the real photo. Both images should be kept and used at the end of the workshop.

6. Cut out 18 pieces of paper and paint 6 blue, 6 yellow and 6 red. Arrange them neatly on one side of the lab table, as in the figure.

7. On the other end of the table, prepare the workstations to paint – each one complete with a white sheet, a paintbrush, a plastic plate for mixing, a plastic cup with water and kitchen paper, so as to dry the brush. Each workstation is assigned to 1/2 participants, according to the number of people in the group.

8. Inflate 6 balloons, two very inflated, two half inflated and two almost deflated. Insert into each one a box, practicing a hole which allows you to put your hand in and touch the balloon without seeing it. The boxes will be used in the second part of the laboratory.

Description of the activity

First Part

1. After mutual presentations, ask the group to give definitions of disorder. For example, you can invite them to think about the status of their own room, on the difference between when toys settled in their place and when they are spread on the floor.

2. Tell them that usually physicists measure disorder, which is defined entropy, in several complex ways, and that today they will be using colors and perfumes to represent them.
Note. From here onwards, repeat, and make them repeat the word “entropy” several times in the course of the activity, per familiarize with this strange word.

3. At this point, make them snuff the vials (the name of the aroma cannot be seen because it is covered by the colored paper) and ask them which smell has been associated to colors.

4. Show the hanging sheets and invite them to come closer to smell them, and ask them what they perceive. Once you collect all the answers, turn the sheets and show the various colors. The white has less disorder of primary colors (and related perfumes), which in turn have less disorder than mixed colors, etc.
Attention! A blue sheet and a red sheet hide the colors below, but the degree of disorder is in any case still perceptible thanks to the mix of smells. The same thing happens in the context of research: sometimes it is useful and necessary to use different tools, as we do with our senses, so to understand a phenomenon better.

5. The colored sheets arranged on the table, explaining that they have been so placed to represent a status which is as orderly possible.
Therefore, move to the other end of the table and have participants sit in the various workstations.

6. Ask them to make any drawing, with just one rule: there must be as much disorder as possible. Give them about 10 minutes for this phase.

7. Once the drawings are completed, study them one by one, together with all participants, asking them to evaluate the degree of disorder in each of them. Some will have mixed colors, others not, therefore they will have high or low degrees of disorder.

8. After discussing how to make a disorderly drawing, substitute sheets and water in the glasses, and ask them to make another drawing, this time with the lowest possible disorder. Once again, give them 10 minutes, then evaluate the degree of disorder all together. Make them notice that, notwithstanding the disorder is smaller in the single drawing, the water in the glasses mixed with color, thus revealing that this is an unavoidable and irreversible process. In order to reinforce the discussion, you can ask participants whether, once mixed the color green, it can be brought back to the blue and yellow state.

9. Conclude, recalling that “strange word used at the beginning, entropy”, a physical quantity which helps us to understand in which direction time flows. Indeed, since we cannot bring colors back to their original state, there is only one time dimension in which the facts occurred: earlier on, we had blue and yellow and then there is green: the opposite cannot happen.

10. A few participants may realize that they could have left the sheet blank (if nobody asks this question, let them notice). Shift the focus on the leaflets of point 6 of the phase of preparation which, because of the wind, jolting table, etc., will have moved from the initial position and will have mixed. Ask participants what happened according to them, remind them that some time has passed since they were last observed, at the start of the laboratory. Ask them: “If we observe them again later, will they be back in place?” Obviously not; on the contrary, they will be even more disorderly. The more time passes, the more disorder increases, thus even though we are doing nothing (leaving the sheet blank), the Universe itself naturally tends to a more disorderly status.

11. At this point, show the drawing of the galaxy, realized in point 5 of the phase of preparation. Tell them that the Universe has gas, stars and dust available, just like participants had three colors available, and mixed them to form these beautiful structures, which, however, are more chaotic. Show also the original image as a comparison.
Therefore, the next time parents will tell you to put your room in order, you can answer: “This is not disorder, its entropy! Even the Universe does it!”.

Second part

12. . If you still have time, take the boxes with the balloons and arrange them as in the figure, namely along two rows, so that in one row, from left to right, you will find an inflated balloon, a half-inflated balloon and a deflated balloon. In the other row, the situation is reversed, with an inflated balloon in front of a deflated one. Attention: the image shows the balloons as an example; we recommend to keep them inside the box, as explained in point 8 of the phase of preparation.

 

 

13. Ask two participants to place themselves in front of the two rows of boxes and invite them to insert their hand and describe what they feel. Repeat the procedure for all three boxes in the row. In case, help them with clues, for example asking them to notice the different quantity of air they contain, and that, while one has perceived the inflated balloon first, the other one has found the deflated one first.
Each path represents the evolution in time of the balloon, and both paths are possible. We can have the balloon that inflated by blowing in, and the balloon that deflates with time
.

14. At this point, pull out one of the inflated balloons, pop a balloon with a needle and ask the group at which end of the table it should be placed. They should answer that it’s going after the inflated balloon. In this way, we identify a direction of the timeline, which cannot be walked backwards, because the exploded balloon cannot come back. Invite participants to think of other daily situations, which can help us define the direction of time, for example: the breaking egg, … Repeat the concept of time as a direction in which entropy always increases. The activity may be adapted in the duration of the two parts, according to participants’ preferences: if the group does not like coloring, or makes the drawings very quickly, give more relevance to the section with the balloons. On the other hand, is they prefer coloring, you can skip the balloon part, and ask them to make a third drawing at will.

Explanation of the physical process

Entropy is the measure of the “disorder” of an object or a physical process, namely of the random distribution of the atoms involved, which corresponds to the number of possible configurations. It can also be interpreted, following the second principle of thermodynamics, as the energy of the system, unavailable to be converted into work.
A system is balanced when the entropy is at its highest, therefore it always tends to increase. Even though a certain phenomenon seems to present a negative variation of entropy (therefore, it has a lower entropy by the end of the process compared to the beginning, for example, water that becomes ice). These systems are not isolated, whereas the total entropy of the Universe increases all the time.
The definition of “time” ist
strictly connected to entropy: the direction or arrow of time is defined by the direction in which entropy increases. This is particularly clear when you observe irreversible transformations: for instance, you cannot put a broken egg back together, or separate the water mixed with the tempera. Even reversible transformations, like putting the sheets spread by the wind in order, require work in order to be done and therefore involve an increase of entropy. Indeed, in each transformation there is always an amount of energy converted into heat, which therefore naturally passes from a warmer body to a colder body, thus causing an increase of entropy.