How
Far Away is the Storm?
When you see a flash of lightning, start counting seconds like
this: "and one and, and two and, and three and"- and
continue until you hear a roar of thunder. Divide the number you
get by 5 (for miles) and 3 (for kilometers). That will give you
a rough estimate of how far away the center of the storm is.
Lightning and thunder take place at the same time, but light and
sound travel to us at different speeds, and so reach us at
different times. Light travels at 186,000 miles (300,000 km) per
second and takes only a fraction of a second to reach us. We see
lightning the moment it flashes.
However, it takes about 5 seconds for sound to travel a mile (3
seconds for a kilometer).
When a thunderstorm is near, the thunderclap sound is loud and
sharp. When it is far away, it is a low rumble. Ordinarily, you
can't hear thunder more than 10 or 15 miles (16 or 24 km) away.
If you see lightning and hear thunder at just about the same
moment, the storm is right above you.
What Causes
Thunder?
You Will Need:
Ballon or paper bag
What to do: Blow up the balloon or the paper bag. Tie it
closed with a rubber band or a piece of string. Then place one
hand on the top and one hand on the bottom of the balloon or the
bag and pop it.
What happens: You get a small clap of thunder.
Why: You created thunder by causing a small quantity of
air to move fast. An object produces sound when it
vibrates-moves back and forth or up and down. Humans only hear
sound when an object vibrates at least 16 times a second- and
not more than 20,000 times a second.
When a flash of lightning passes through the atmosphere, it
heats the nearby air, and causes it to expand rapidly. It is
this movement that causes the sound. A short crash of thunder
results from a short flash of lightning. Rolling thunder occurs
when lightning covers a large area, or when clouds, mountains,
or other obstructions cause echoes.
Making
a Bubble Blower
You Will Need:
Uncoated wire clothes hanger
Circular object, like a frozen juice can, or a thick crayon
Bubble mix
What to do: With the help of an adult, untwist the wire
hanger and then wrap a piece of it around the can or thick
crayon. Slip the can out. Leave about 4 inches (10cms) of
straight wire for a handle.
Then bend the rest of the wire back and forth until it snaps.
And now you have your bubble wand.
Dip the wand into the bubble mix and wave it in the air.
What happens: You get a spray of bubbles.
Why: By waving the soapy wand in the air, you add the air
that forms the center of each bubble.
Upside
Down in a Spoon
You Will Need:
A shiny big spoon
What to do: The scoop of a spoon makes an interesting
mirror. Just be sure the spoon you use is shiny and the larger
the better. Hold the spoon up so you see yourself in the scoop.
What happens: When you look at the spoon you'll see your reflection
upside down. Tip the spoon so it reflects other things that also
appear upside down..
Why: Light rays travel in
straight lines. They are reflected in straight lines, too. But
when light is reflected from a curved surface, the rays leave
the surface at different angles. The reflected images appears
upside down because of the angle of the reflected rays of light.
Paper Napkin Trick
You Will Need:
Paper Napkin
Plastic cup of water
What to do: Drape the napkin over the edge of a kitchen counter or table. Place the plastic cup of water on one corner of the napkin about 1 inch (2.5 cm) from the edge.
Pull the napkin quickly away from under the plastic cup.
What happens: The napkin comes out-without any water spilling.
Why: The cup doesn’t overturn because of the tendency of things at rest to stay at rest. It’s that old law of motion-inertia-at work. If it does spill it’s because you’re not pulling the napkin fast enough or with enough force.
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