Hobbies And Interests
Swing Don't Spill
While most adults have either intentionally or accidentally performed this basic science experiment on centripetal force, kids are amazed and delighted when they first try it out for themselves. Fill a small bucket with a handle halfway with water. Tie a 3-foot length of rope to the bucket handle. Have the child wrap the other end of the rope around his hand a couple of times. This is best done outside where you have plenty of room. Instruct the child to spin the bucket rapidly in a vertical circle so that the water remains in the bucket. Next, test how slowly the child can swing the bucket without spilling the water. This demonstrates centripetal force, or the inward force on a rotating object. Explain how the water is falling but the bucket is falling at the same speed. When the spinning motion is slowed, water begins falling more quickly than the bucket and spills.
Air Can Crush
Show kids how air pressure can crush a soda can. Collect an empty soda can, a 2- or 3-quart saucepan and kitchen tongs. Fill the saucepan with cold water. Put 1 tablespoon of water in the can. Heat the can on the stove until the water boils. You'll know when this happens because steam will escape through the open tab of the can. Allow the boiling to continue for 30 seconds then place the can in the pot of cold water, using the kitchen tongs. The can will collapse. Explain that when the water boiled, air was pushed out of the can. Water vapor filled the can, and then the vapor was suddenly cooled by submerging the can in the pot of cold water. When the water vapor was cooled it condensed, creating a partial vacuum that allowed the air pressure outside the can to crush it.
Paper, Parachutes and Terminal Velocity
This experiment requires a ping-pong ball, sheets of paper and a parachute devised from paper or cloth. Drop sheets of paper from a horizontal position and note how they fall. Next fold sheets of paper into little trays with sides approximately 1 inch high. Drop the trays right-side-up and upside-down and note how they fall. Next drop the ping-pong ball, observing how it falls. Finally, make a simple parachute from cloth or paper with threads hanging down the sides. Tape the ping-pong ball to the threads. Note how it falls in comparison. Talk about what it means to be streamlined, and how less of the surface meets resistance when something is streamlined. Terminal velocity is achieved when upward forces are equal to the weight of the falling object.
Recreating Galileo's Famous Experiment
Pose the question to children: Do heavier objects fall faster than lighter objects? Climb a ladder or stand on a balcony and drop objects at the same time from the same height while the children videotape the results. Sample objects can include a tennis ball and a basketball, a toy and a candy bar, etc. Repeat the experiment a few times to verify the accuracy of the results. Experiment using using two objects of the same weight or mass but of different shapes as well as objects of the same shape but different mass.