Science experiment to understand evaporation

Evaporation is an interesting Science concept. But, it is often confused with boiling. The reason for confusion may be because in both the processes, water changes from the liquid state to gaseous state. Let us dig deeper and understand evaporation better. Here are some common misconception about evaporation that many students have:

• When water evaporates, it no longer exists.
• When we sweat, water is absorbed into the skin.
• Evaporation and boiling are the same.

So, what is the difference between evaporation and boiling? What are the factors that affect evaporation? We will attempt to answer these and many other questions in this article. Let us first ask you a WOW question.

WOW Question:

In a typical October in Bangalore, we placed 200 ml of water in a tumbler to dry up. Can you guess how many weeks will it take to dry up all the water? The correct answer will make you say WOW!

(The average temperature is 22°C. The average humidity is 78%. The room is closed with no wind.)

Pause and think for a few seconds. Would it be a few minutes? A few hours? A few days? Or, will the water never dry up?

When you are ready, watch this video to find out the correct answer:

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We conducted this Science experiment in our lab in Bangalore. During the experiment, we noted our observations every week. There was a significant water loss after week 1.

After six weeks, we noticed that the tumbler was half full. As time shifted to the 10th, 12th and 14th weeks, less water remained in the tumbler. After the 16th week, the tumbler was completely empty. The water had completely disappeared almost magically!

Did you like this experiment with water in a tumbler? Did the result surprise you? We found it amazing to notice that the water had slowly and steadily vanished.

This is a simple science experiment that you can even try at home. We will evaluate this experiment in a great detail. But, first here are some question to think about before reading on:

Q1. Where did the water in the tumbler go?

Q2. Is it possible to speed up this process of evaporation?

Take a minute to think. Once you are done, let us note our observations to the questions that we asked at the beginning of this article.

1. What is the difference between Evaporation and Boiling?

- The level of water decreases even without heating the water. The evaporation happened at room temperature. Boiling requires an external source of heat. Evaporation uses the energy of the water to push molecules to escape the water. Hey, water stores a lot of heat! This is why we feel colder when our sweat evaporates from our skin.

Next time don't wipe your sweat. Let it evaporate and cool yourself off!

- The process happens at a very slow rate. It took 16 weeks for the tumbler to dry up. Boiling happens at a much faster rate.

- When you boil a liquid, you can see the bubbles first form at the bottom of the container and then bubbles start rising up. You can see the entire volume of water boiling. Evaporation, on the other hand, happens only at the surface. There are no bubbles produced.

- Evaporation happens at any temperature. Boiling starts to happen at a certain temperature. This temperature is called 'boiling point'.

2. What are the factors that affect evaporation?

- Temperature: When we increase the temperature, the molecules of the liquid start moving faster. This makes it easier for molecules to escape the liquid.

- Surface Area: Evaporation happens at the surface. When we increase the surface area of the liquid, the rate of evaporation increases. So, the next time you want your glass of milk to cool faster, you know what to do.

- Wind speed: If the surrounding wind is moving faster, it increases evaporation. You would notice that during winters, water condenses on your windscreen. Can you use the factor of windspeed to make this water vapor go away?

- Humidity: Humidity is the amount of water vapour present in the atmosphere. If humidity increases then it means that the air is filled with more water vapour. And this means that more water is condensing and returning to the liquid. This slows down the rate of evaporation. To explore this factor, you can take two tumblers: one with its lid open and one with its lid closed. Which tumbler do you think will empty faster due to evaporation?

We hope that this article made you think. Did you learn something new about evaporation today? Stay tuned for more WOW Videos.

Here are some more questions to make you think about evaporation:

1. When the sweat dries from your skin, is it evaporation or boiling that is happening?
2. Can you guess in which city - Delhi or Mumbai - is evaporation likely to be faster?
3. You want to dry your clothes in your room since it is raining outside. You have just understood the factors that affect evaporation. What can you do to make your clothes dry faster.
4. After you take a bath, the water from your hair vanishes in a few minutes. Why is the evaporation so fast in case when it took 16 weeks for the water in the tumbler to vanish?
5. In summers, we switch on the fan. How does switching on the fan make us feel cold?
6. What are clouds made up of?

If you are interested in Science, you should explore Open Door's application: Unbox Physics. Unbox has many interesting questions and experiments that are designed to make you a brilliant thinker. Unbox Physics currently helps you explore the following modules in Physics: Force, Pressure, Light, Heat, Sound, Electric Charges, Motion, Units and Measurement.

The app is available on both Google Play Store and Apple Store.