Sounds cool, right? Your students will enjoy exploring this STEM topic and being able to apply what they’ve learned as they encounter the summer heat. Check out the following activities to learn about heat energy in your afterschool program.

1. How Heat Affects Molecules

We explained earlier that heat energy causes molecules in an object to behave in a certain way: when an object is hot, molecules move fast. When it’s cold, they move slowly. But what does that mean? In this simple heat experiment, students will better understand how molecules act in cold, hot and warm temperatures.


  • 3 clear jars
  • Water
  • Food coloring
  • Masking tape
  • Markers
  • Thermometer (optional)


  1. Fill one clear jar with warm water. You can either adjust the faucet until the temperature of the water is 72 °F or let it sit out for the day until it becomes the same temperature as the room. Use the masking tape and markers to label this jar ‘Room Temperature.’
  2. Fill another clear jar ¾ of the way with cold tap water. Add ice cubes to make it even colder or place it in a refrigerator to stay cold while you wait for the ‘Room Temperature’ jar. Label this jar ‘Cold Water.’
  3. Fill the last clear jar with hot tap water. You can even heat the water on the stove. Be sure to provide adult supervision with this step to prevent burns. Then label this jar ‘Hot Water.’
  4. Add a drop of food coloring to each jar and observe what happens over time.

As expected, the food coloring spreads out fastest in the hot water and slowest in the cold water. Eventually, it spreads out in all three jars. This is a cool way to demonstrate how heat energy affects molecules in an object.

2. Understanding the Effects of Dehydration

One of the biggest concerns during the summer is the risk of dehydration. This is a significant loss of body fluid due to heat, excessive activity, not consuming enough liquid or excessive sweating. Dehydration can affect normal body functions and cause dizziness, rapid breathing, lack of energy and even fainting. Use this STEM experiment to demonstrate the effects of dehydration on potatoes.


  • 1 potato (small or medium size)
  • 2 dishes or saucers (deep enough to hold about a half-inch of water)
  • Cutting board
  • Knife
  • Salt (about 2 tablespoons)
  • Water
  • Piece of paper
  • Pen, pencil, or marker
  • Adult supervision


  1. Place both dishes on a piece of paper and label one ‘salted.’
  2. Fill each dish with an equal amount of water. Be sure that the water doesn’t overflow.
  3. Stir two tablespoons of salt into the dish marked "salted'.
  4. Cut the potato in two equal halves (this step should be completed by an adult).
  5. Place one-half of the potato in the salted water and the other half in the plain water. Both should be flat side down.
  6. Let them sit in the water for an hour. Once the hour is up, observe the results.

The potato in plain water is mostly unchanged; however, the potato in salted water will be shriveled. This is because the salt - which acts as a dehydrator - drew the water out of the potato, causing it to get dehydrated and shrivel. Similarly, dehydrators - like sweat - can draw water from our body. Losing too much water without replenishing can impact our heart, lungs, kidneys and other major organs. To stay hydrated, especially in hot temperatures, be sure to drink at least eight cups of water or more each day.

3. Why Do We Sweat? 

Everyone sweats when it gets hot, but why exactly do we sweat? As outside temperatures rise, our bodies release liquid sweat in an effort to regulate our internal temperature. As the sweat evaporates, it removes heat from our skin and makes us feel cooler. The following experiment will help students understand how sweating helps keep their body cool. 


  • Outdoor thermometer
  • Cotton ball
  • Rubbing alcohol
  • Watch


  1. Lay the thermometer on your work surface for five minutes so that it will register at room temperature.
  2. Wet the cotton ball with alcohol.
  3. Lightly rub the wet cotton ball across the bottom bulb of the thermometer.
  4. Blow lightly on the wet cotton for about 30 seconds. Observe what happens to the temperature reading.

Similar to sweat, the alcohol on the cotton ball began to evaporate and draw heat energy from the mercury in the thermometer. This caused the mercury to contract and move down the thermometer, giving a lower temperature reading. Sweat plays an important role in keeping us cool during those hot, summer days.

4. Which Colors Absorb the Most Heat?

Did you know that wearing dark-colored clothing in direct sunlight can actually make you feel hotter? With this experiment, students will create solar bowls to determine how - and why - dark colors attract more heat.


  • Water
  • 3 same-size bowls
  • Yellow, blue, green and red food coloring
  • Clear, glass dish
  • Sunshine


  1. Pour two cups of water in each of the three bowls.
  2. Put a few drops of yellow, blue, green and red food color in two of the bowls. The water should look black from the mixture of colors.
  3. Cover one of the bowls of dark water with a clear glass plate or clear baking dish. The third bowl has plain water and no cover.
  4. Leave all three bowls in the sunshine for several hours.
  5. Test the temperature of the water in each bowl with your finger.

The dark water in the covered bowl should be the hottest. Solar energy obtained from the sunlight passes through the clear covering and becomes trapped inside the bowl. The dark-colored water, which absorbs all wavelengths of light, absorbs the solar energy and converts it into heat, causing the water to be warm. Similarly, when people wear dark clothing on hot days, it will attract more solar energy from the sun and turn it into heat, causing them to feel warmer than they would if they wore lighter-colored clothes. 


Do you have any other fun heat science experiments for students? Share them below!