Schools often conduct science fairs to encourage students to think creatively and critically about their environment and the way the world works. Even outside of science fairs, projects allow students to test and demonstrate their understanding of science. Comparison projects emphasize the importance of controlling variables and monitoring the effects of changing a single variable. Students can identify variables, isolate reactions and demonstrate knowledge of the scientific method.
Using six Mason jars, salt, water and a half-dozen hard-boiled eggs, students can see the effect that adding salt to water has on density. Fill each jar with the same amount of water and add increasing amounts of salt to each jar. Place a hard-boiled egg in each Mason jar and observe the level at which each egg floats. As the salt concentration increases, the density of the water increases and the egg floats proportionally higher. Advanced students can measure the salt concentration and level at which the egg floats and plot the data points.
Fill two clear plastic bottles with water. Test several clear sauce-packets in a bowl of water to find a packet that barely floats. Insert one packet in each bottle, fill the water to the brim and screw each cap back on. Set one on a flat surface and apply pressure to the sides of the other bottle. The packet in the bottle being squeezed sinks as the increase in pressure decreases the volume of the air trapped in the packet thus increasing the density of the packet.
Heat two separate pots of water. Insert a thermometer in each pot and add a tablespoon of salt to one pot of water. Watch the pots and record the temperature at which each pot begins to boil. The pot with salt dissolved in the water boils at a higher temperature than the pot without dissolved salt. This experiment can be repeated to find the relationship between amount of salt dissolved and increase in boiling point.
Compare the lifespan of batteries using a flashlight and a clock. Insert the batteries of one brand into the flashlight, turn the flashlight on and record the time. Check on the flashlight in regular intervals and record the time that the light goes out. Find the positive difference between when the light turned on and when the light turned off to determine the lifespan of the first brand of batteries. Repeat the experiment with each brand of batteries and compare the lifespan of the brands.