Children are curious about how the doctor can hear their heartbeat through a stethoscope. You can make one at home using an old garden hose and funnel. Begin by cutting a length of hose 12 to 14 inches long. Attach one end to the funnel. Put the funnel up to your heart while your child uses the other end of hose to listen to your heartbeat. Sound generally spreads out in all directions, but the hose directs the sound of the heartbeat so it can be heard even though it is a quiet, usually inaudible, sound. A variation of this project is to try other hollow materials and see with which one the heart beat is heard most clearly.
This project shows how materials with the same charge repel each other. Tie two blown-up balloons together with a piece of string or yarn. Hold out a 12- to 14-inch stick and hang the balloons over the stick. Rub each balloon with a piece of wool or wool sweater. Rubbing them with the wool gives them the same static charge. When you let go of the balloons they will push away from each other. You can then separate the balloons and rub them again with the wool. The strong static charge will make the balloon stick to the wall.
Making invisible ink is a science project that demonstrates a chemical reaction. The key to success is to use fresh lemon juice. Squeeze the juice of a lemon into a bowl. Using a paintbrush or a capped pen write a message on a piece of white paper. When the lemon juice dries it will be invisible. To make the message visible an adult can place the paper in a 350-degree oven for eight to 10 minutes and the message is then revealed due to the chemical change in the lemon juice. An extension to this project is to recreate the experiment using other fruit and vegetable juices.
The project demonstrates how create a frost pattern. If the environment is warm the water vapor in the atmosphere condenses to form dew. In a cold atmosphere frost will appear. To recreate this at home take a clean glass plate and spread petroleum jelly in a design on the plate. Put the plate in the freezer next to a glass of very warm water. Let stand for several hours. The water vapor will condense in the freezer to form frost on the parts of the glass plate that does not have the the petroleum jelly design.