Make Air Pressure Hold A Plate
This could get messy so work over a sink. Even better try this outdoors.
You'll need:
A study plastic plate
A paper towel
A sturdy plastic glass (juice size works best)
Fill the plastic glass nearly full of water. Fold the paper towel into fourths and place it on the middle of the plate. Next, turn the plate and towel over the cup like a lid. Hold the plate against the top of the cup with your fingers while you turn the whole system over.
Now the glass is on top. Be sure it is straight up and down. Hold on to the cup with the hand that isn't pressing up on the plate. Then--slowly--take your hand away from the plate. The plate won't fall and the water will stay inside the glass.
Air pressure makes this work. Even though it's invisible, air has weight and takes up space. Air is also al around you so it exerts force on you and objects and other people from all directions. As gravity pulls down on the water inside the glass a partial vacuum is created in the air-filled space inside the glass. Now the downward force of the water and air inside the glass is less than all the upward pushing force of air on the plate. You can see how much larger this surface is than that covered by the water inside the glass. The wet paper towel helps by making a tight seal between the glass and the plate. This keeps any air from slipping inside the glass. If that happened, the air rushing into the glass would push the water out. Then there would be a flood and you'd get wet.
Use Air Pressure To Plug Leaks
You'll need:
an empty 1 or 2 liter plastic soft drink bottle with a screw-on cap.
3 pushpins (the kind used to display things on a bulletin board)
Work outdoors or at the sink. Fill the bottle to the very top with water. Screw on the cap, making sure it's tightly sealed.
Next, stick the pushpins into the bottle, one at a time. Then have your adult partner hold the bottle by its cap while you carefully twist and tug out the pushpins.
Surprise! If water leaks out at all, it quickly stops or slows to a tiny trickle.
Did the bottle magically plug the holes? Of course not. Squeeze the bottle to prove it. Water will spurt out the holes. But when you stop squeezing the water will immediately stop flowing.
The magic is that air pressure is at work again. Air doesn't simply push down, it exerts force in all directions. The force of the air pushing in on the water at the holes you made is greater than that of the water inside the bottle pushing out.
What do you think will happen when you take the cap off the bottle, letting air push down on the water inside the bottle? Try it--just be sure the bottle is over the sink.
Make Air Vibrate and Create Squawky Cans
Want to make strange sounds? You can with a little help from science.
You'll Need:
two cans of different sizes (cleaned and dried)
Sturdy packaging twine
2 paperclips
scissors
tape
a piece of clean sponge (about 1 inch by 2 inches)
Have an adult partner use a nail and hammer to punch a hole through the bottom of each can. The hole should be just big enough for the twine to slip through.
Next, cut a piece of twine about twice as long as the can's height. Thread one end of the twine through the hole and tie to a paper clip. Rest the paper clip on the can bottom and tape in place. Repeat these steps with the second can.
Now, wet the sponge and squeeze out the water.
To make your can squawk, hold the can in one hand. With the other hand, pinch the sponge against the string and give it a jerk. This makes the metal-can bottom vibrate. That in turn creates waves of air. When those waves reach your ear and your brain interprets the signals it hears, you hear the spooky noises.
To make your can squawk, hold the can in one hand. With the other hand, pinch the sponge against the string and give it a jerk. This makes the metal-can bottom vibrate. That in turn creates waves of air. When those waves reach your ear and your brain interprets the signals it hears, you hear the spooky noises.
Can you think of some other things you could make vibrate to produce squawks and weird noises? You'll probably think of lots more but here are three to get you started:
A balloon--Blow it up and grip it between your legs so you can use both hands to stretch its neck Then control how much air escapes.
A comb--Hold it in one hand and run your fingernail back and forth across its teeth.
An empty glass soda bottle--Put the rim next to your lower lip and blow a strong blast of air across the opening.
Use Fast Moving Air to Float A Ball In Mid-Air
A blowdryer makes this science magic trick happen.
You'll need:
A blow-dryer
A Ping-Pong ball
Hold the blow-dryer with the nozzle aimed straight up. You may want your adult partner to do that for you. When the dryer is switched on to "high", place the ball in this column of fast-moving air so it's about 5 inches above the nozzle. Let go of the ball and quickly take your hand away.
As long as the air current iss shooting striaght up, the Ping-Pong ball will float suspended above the dryer's nozzle.
This "magic" happens because fast-moving air has less pressure than more slowly moving air. So the Ping-Pong ball is trapped inside the column of fast-moving air. Here the ball is pushed upward by a jet of air with enough force to keep it from falling, but not enough to blow it any higher.
What you've discovered is also the basic law of nature that helps airplanes fly. When viewed on edge the upper surface of an airplane's wing is curved and the lower surface is flat. Air slips over a curved surface more quickly than it does over a flat surface. So there is less air pressure on the upper surface of the wing than there is beneath the wing, giving the airplane lift.
Can you guess why airplanes take off into the wind?
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