As with any science fair project, follow the scientific method when developing your experiment. This includes forming a question about the natural world and researching that question. Then, using your research as a guide, form a hypothesis about what will happen in an experiment. Test your hypothesis using controls and variables, then analyze your results and draw a conclusion from them. Remember to only use one variable for what you're testing because then you are certain that the variable is what caused any changes in the results.
One variable to consider is how different liquids evaporate. Most people think of water as a liquid that evaporates readily, but there are many other liquids that also go through the process. Suggested types of liquids to test include water, rubbing alcohol and vegetable oil. With proper supervision, volatile liquids like lighter fluid or nail polish remover can also be tested. Test these liquids by laying the same volume of each out in the exact same conditions and time how long it takes for them to completely evaporate away.
The amount of heat in a liquid, or the temperature of the surrounding air, can impact the rate of evaporation. Test this variable by placing the same volume of water in similar containers in differently heated locations. One way to achieve this is to place one container in the corner of a room while the other is placed near an incandescent light bulb or heater. For added accuracy, use thermometers to measure the surrounding temperature of each location.
One factor that greatly affects the rate of evaporation is the surface area of the liquid exposed to the air. Test this by adding the same volume of water to different-shaped containers. For example, place a volume of water in a pie plate, in a beaker and in a graduated cylinder. As a control, place the same volume of water in a sealed container, which results in zero exposure to the air. Measure the area of each surface that is exposed to the air and measure how long it takes for each one to evaporate.
Everyone has experienced how air circulation affects the rate of evaporation when they feel a breeze after sweating. Moving air can cause water to evaporate quicker. This can be tested by placing the same volume of water in similar containers. Expose them to the open air at the same temperature, but place a fan next to one to ensure a steady current of air. To further experiment, use different setting speeds to the fan. Time how long it takes for each to evaporate and communicate the results.
If you have ever seen how fast rain evaporates off the ground after a brief shower in a dry climate, you have seen how low humidity can affect evaporation rates. Test this by placing the same volume of water in similar containers and place them at approximately the same temperature in places with varying humidity. Options for this are placing the container in the high-humidity environment of an indoor pool or a greenhouse compared to the low humidity environment of a computer lab or climate-controlled building.