Learning Lesson: Diet Light


Objects float if they weigh less than the weight of the water they displace. Conversely, objects will sink if they weigh more than the weight of the water they displace. Students will observe how the added sugar in a can of soda affects its density and thus its ability to float in water.

TOTAL TIME 3 minutes
SUPPLIES One can of soda (Coca-Cola, Pepsi, RC, etc.) and one similar brand of their "sugar-free" soda; Fish tank ¾-filled with water
SAFETY FOCUS Thunderstorm safety rules


  1. Place the regular soda at the bottom of the tank of water.
  2. Place the diet soda at the bottom of the tank. Observe what happens.
  3. Remove both cans and have a student come up to verify that the cans have not been tampered in anyway.
  4. Place both cans back into the water.
  5. Have the students try to explain why one floats and the other does not.


While both cans displace the same volume, the diet soda will float and rise to the top. Look at the ingredients on each can. The regular soda has approximately 40 grams of sugar that the diet soda does not contain. The added sugar increases the density of the fluid in the can to the point where it now weighs more than the weight of the water that is displaced by the volume of the can.

Understanding density is important for understanding weather. Warm air is less dense than cold air. Additionally, as the moisture content of the air increases, the less dense it becomes. In both cases, the less dense air rises easier. Increasing both the heat and humidity can lead to rapidly rising air, which can produce thunderstorms.

Building a Weather-Ready Nation

A Severe Thunderstorm Warning is an urgent announcement that a severe thunderstorm has been reported or is imminent and warns you to take cover. Severe thunderstorm warnings are issued by local NWS offices.

  • Seek shelter, but avoid trees as these are targets for lightning.
  • If indoors, stay away from windows, and go to the safest location on the lowest level of your home.
  • When boating, always stay tuned to the latest weather reports, and return to safe harbor before the strong winds arrive.
  • Mobile homes are especially vulnerable to the high winds of a thunderstorm and are subject to overturning and rolling if not properly anchored to the ground. Professional advice should be obtained from a reputable mobile home contractor. At a minimum, though, the frame should be secured with heavy steel straps. Heavy straps should also go over the top of the home with both frame and over the top ties secured in concrete footings.