Evaporation
by Chris Tilley
All experiments require adult supervision.
This is the first of our science experiments. I do these with my children aged 5 and 7. They don’t always work out as expect as you will see but that just gives us an opportunity to examine our methods. Todays question was about evaporation. The kids knew about evaporation and the water cycle from watching Magic School Bus. They wanted to know how fast water evaporated and what affected it. We decided to focus on temperature and as a second factor the surface area of the contained.
Question 1: Does the air temperature affect the rate of evaporation?
Question 2: Does the the shape of the container affect the rate of evaporation?
Next we had to figure out how to do this experiment. First we were going to need to measure the temperature and the amount of water left. A thermometer provided the temperature and a scale, the amount of water left. I used the scale because it had an accuracy in grams and I knew that the evaporation would be small. I would recommend a prober outdoor thermometer. I started with a meat thermometer that work fine to start but started giving flaky results at which point I switched to our thermostat that has a outdoor temperature reading but the sensor is in the shady side of the house, not perfect. We used a bowl for on and a glass for the second both made of glass and put in the same amount of water. We then measured the temperature and the amount of water every hour.
Method:
- Select your containers. One should be wide topped the other narrow
- Find an outdoor thermometer.
- Find a digital kitchen scale.
- Place the smaller of the containers on the scale.
- Add water to the container till near the top but not in danger of spilling.
- Write down the starting weight of water and container for container 1.
- Take off the first container.
- Put on the second container.
- Add the same amount of water.
- Write down the starting weight of water and container for container 2.
- Put both containers and the thermometer outside in the sun. Its best to start in the morning to get a wide range of temperatures.
- Write down the time and the temperature.
- Come back in an hour. Take the temperature and weight the containers. Write those numbers down along with the time.
- Repeat ever hour for as long as reasonable.
Our results
Time | Jar Weight (g) | Difference (g) | Bowl Weight (g) | Difference (g) | Temperature (celsius) |
---|---|---|---|---|---|
12:27 | 392 | — | 372 | — | 21.0 |
1:27 | 391 | 1 | 369 | 3 | 21.5 |
2:27 | 389 | 2 | 363 | 6 | 22.5 |
4:12 | 386 | 3 | 356 | 7 | 24.0 |
5:12 | 385 | 1 | 352 | 4 | 23.5 |
So we can see that the increasing temperature did have an affect on the evaporation rate as did the shape of our vessel. There are other things that affect the evaporation rate. Temperature of the water at the surface, humidity, water currents and air flow. (source) So I should have measured the temperature of the water because it would have been changing as I pumped energy into it and because it holds it temperature well it would have stayed higher even after the air temperature dropped. The rest would have been relatively constant throughout our experiment.
The important thing was showing that increasing the temperature did increase the evaporation rate and that has implication in a warming world.