Demonstrate the greenhouse effect using a tomato plant on which the tomatoes are just starting to grow. Thread a 2-liter bottle over one of the tomato plant's branches so the branch is inside the bottle. Secure the bottle to the plant's stem with tape. Leave the plant somewhere where it receives plenty of sunlight and continue to water it regularly. The tomatoes inside the bottle will grow faster than those outside. The sun's ultraviolet rays pass through the bottle, but the energy radiated by the heated plant is trapped inside, raising the temperature so the tomatoes ripen more quickly. Inform your young scientists that this is called the greenhouse effect.
You can explore acid-base reactions by making a glass of fizzy lemonade in this chemistry demonstration. Fill a glass with equal amounts of water and lemon juice and stir. Continue stirring and add a tablespoon of baking soda, which will cause the lemonade to fizz. Explain to the children that the lemonade is fizzy because of the reaction between the acidic lemon juice and the basic baking soda, which results in the release of carbon dioxide. Finish the demonstration by adding sugar to the lemonade to sweeten it, then serving a sample of the beverage to your students.
Test the melting points of different substances, such as candle wax or chocolate, with this physics demonstration. Explain to your students that a solid's melting point is when it turns from a solid to a liquid. Place the substances one at a time in a microwave-safe bowl and heat in a microwave oven until they are completely melted. Ask a volunteer to time how long each solid takes to melt. Measure the temperature of the liquid with a food thermometer. Inform your youngsters that the melting points of different solids depend on their density and the way their molecules bond together.
You can capitalize on your science demonstrations using household items by emphasizing the importance of health and safety. Explain to your young scientists that even when an experiment appears to be relatively safe, it is important to make sure it stays that way. For example, in the melting points demonstration, you should use oven mitts or pot holders to remove the bowls from the microwave. Inform your youngsters that science experiments should never be carried out without wearing the appropriate safety clothing, such as safety goggles, white laboratory coats and rubber gloves.