A person's sense of smell dictates what she tastes more than the actual taste of the food. Most fourth graders do not know the vital role the nose plays in making food taste great, so performing an experiment to show how scent effects taste fascinates them. Have your fourth grader bite into a slice of apple without swallowing it. Tell her to think about the taste to determine if it is sour or sweet. While she is focusing on the taste of the apple, place a cotton ball soaked in vanilla under her nose. The scent of the vanilla should make her taste the vanilla instead of the apple.
Nerve endings run all through your body, but some locations are more sensitive than others. Have your fourth grader test his friends' touch sensibility to learn about how nerve endings work. Have him write a list of parts of the body, like arms, forehead and neck. Purchase four different spools of flexible wire that all have different widths. Tie a 4-inch piece of wire from each spool to a separate popsicle stick so 2 inches of the wire hangs down. You will have four popsicle sticks with wire attached. Write the gauge of the wire on each popsicle stick. Dangle a piece of wire (smallest gauge first) over a test subject's arms, forehead and neck. If the test subject does not feel the wire immediately, switch to a thicker gauge until he feels it. Record the results to determine where he was most sensitive.
The human eye actually perceives information upside-down instead of right-side up. The image gets flipped by the brain so everything looks right when you register it. A pinhole projector show your fourth grader how this occurs. Punch a hole into the bottom of a plastic cup using a sewing pin. Do not use a clear cup. Place a piece of wax paper over the opening of the cup and use a rubber band to hold it in place over the lip of the cup. Turn off all the lights in the room except a lamp and have him peer through the wax paper. The image through the hole at the bottom of the cup should be upside down on the wax paper.
Ants are interesting to observe at teach your fourth grader a lot about her culture. Start an ant farm in a thin glass container to let her observe the way the ants construct a colony and distribute food. She will see the ants' ability to carry objects much larger than themselves, and will observe how the worker ants cater to the queen in order to keep their society fruitful and growing. Have the student experiment with different food sources for the ants to determine what they like best. She may also set out heavy obstacles to see how the ants handle barriers.