Most of the great scientific discoveries in history began when someone noticed something interesting happening. This is the first step of the scientific method, which is is crucial to accurate research. The scientific method should also form the cornerstone of your high school science fair project, so before you begin experimenting, become familiar with it. For a more successful project, choose a topic that interests and inspires you.

Athletes and hikers often use chemical cold packs for minor injuries because they do not need to be kept in the freezer. When you squeeze the cold pack, a bag of water inside breaks, and the water mixes with the surrounding chemical ingredients. This results in an endothermic reaction, which means that the mixture absorbs heat from the surrounding environment. The pack becomes cold quickly, and typically stays cold for 15 minutes to one hour.

In this project, you will test which of four chemicals makes the best cold pack. Obtain all of the supplies for this project from a standard high school chemistry laboratory. You'll need ammonium nitrate, ammonium chloride, sodium chloride and calcium chloride. For your safety, do not mix any of the chemicals with each other. Wear gloves, goggles and a safety apron.

Use five small Styrofoam cups adding the same amount of distilled water to each of them. Label them with the names of the four chemicals and one for control, which will only have water in it. Record the initial temperatures and then add the chemicals to their respective cups. Check their temperatures again, and then every 30 seconds until the temperatures stabilize. Calculate the temperature changes after each interval, and from the beginning until the last measurement. Consider which mixtures had endothermic reactions, and what kind of reactions the other mixtures had. Note which mixtures had the greatest temperature drops. Repeat this experiment at least twice more to ensure results are correct. You can also try mixing different amounts of each chemical with the water to determine whether higher concentrations of any chemical cause greater or longer-lasting temperature changes.

Aristotle examined the question of whether hot water freezes before cold water in approximately 350 B.C., but even now, scientists can't agree on this seemingly simple inquiry. In 1963, a high school student in Tanzania named Ernesto Mpemba brought the question back into the scientific community’s awareness when he asked a professor from a nearby university about it. Despite teasing from his classmates and schoolteacher, Mpemba insisted that he had seen hot liquids freeze faster than cold liquids many times. The professor, Denis Osborne, conducted a series of tests with Mpemba, and they concluded that hot water did freeze faster. They published their findings, and the phenomenon became known as the Mpemba effect.

For this project, your objective is to determine if hot water freezes before cold water does. Before you begin, state your hypothesis about the Mpemba effect. Prepare yourself by learning about the behavior of water molecules in different temperatures. Think about any factors that might influence your experiment and how to make your hypothesis more specific, if necessary. Consider factors such as the volume of the water, the material of the containers, the method of freezing, the initial temperatures of the water, and the water's source. Do multiple trials under different conditions, to ensure that you are thorough in your examination of the subject. In your conclusions, explore why such a simple question still eludes widespread agreement among scientists for more than 2,000 years.

An increasing number of households are making efforts these days to help the environment through methods such as recycling and purchasing environmentally safe or green products. These products make claims of being environmentally friendly. Used to irrigate plants or water the lawn -- gray water -- which does not include water from the toilet -- also comes from dishwashers, showers, bathtubs and washing machines. Since green products that go down the drain might end up being part of a gray water system, they should not have toxic effects on plants and animals. In this project, develop a hypothesis about whether green dishwasher detergents are less toxic to the environment than conventional dishwasher detergents. Then test your hypothesis by exposing worms to incrementally larger concentrations of each detergent.

The project requires two brands of green liquid detergents, two conventional brands, 14 Styrofoam cups, potting soil, aluminum foil and about 350 live worms, available from bait stores. Each trial represents each of the detergents. Repeat each trial at least three times for accuracy. Label seven Styrofoam cups with the name of the detergent and the percent concentration, beginning with 0 percent on the first cup for the control. Increase the percentage with each cup until the last cup is labeled 100 percent. Fill each cup with water and mix in enough detergent to create the labeled concentration. The first cup only holds water and the last cup only has detergent.

Poke holes in the bottom of seven empty cups. Label each cup to match each of the detergent cups and one water cup. Place 100 grams of potting soil in each empty cup, and stir in five milliliters of the corresponding detergent mixture. Place four worms in each cup. Cover these cups with aluminum foil and store them in an area away from cold, heat or direct sunlight. Repeat these steps for the other three detergents. In five days, observe the number of worms still alive in each cup. All of the control worms should be alive. If they are not, repeat the experiment, but change some of your methods to ensure the worms are not dying for other reasons.

Graph the results, and draw conclusions by determining if the green detergents are nontoxic, and whether the detergent's concentration affects toxicity. You can also try this experiment with plants, or different household products that might also be present in reused water.