Tricks with heat
These tricks aren’t really magic—they just look mysterious. Heat
energy makes them work.
Water ballet
Materials
crayons
ice-cube tray
mixing bowl (large)
paper
scissors
water
You can entertain your friends with a water show small enough to fit
into a mixing bowl. The real performers are the ice cubes!
Draw and cut out some tiny performers the size of the ones shown here.
Use your crayons to color both sides.
Fill the ice-cube tray half full with water. Put the tray in the freezer
until a little ice forms on top. Then take the tray out and lay a
\”performer” on each cube.
Carefully pour in more water until the tray is full. Then freeze the
cubes until they are solid.
To put on a water show, fill a large bowl
with warm water. Then put two or three cubes in the bowl. In a minute or
two the tiny ice-cube figures will begin to flip and turn.
What makes the figures turn over? When you put the ice cubes in warm
water, the bottom of each cube begins to melt. The molecules mix with
the water in the bowl. Soon the top of the ice cube is bigger and
heavier than the bottom. So the ice cube flips over. As the new bottom
side melts, the ice cube flips again.
Which coin?
Materials
box
pennies (5, with different dates)
Have some friends help you with this trick. They’ll give you the answer
without knowing that they have!
Show your friends five pennies in a small box. Explain that you can read
your friends’ minds—that you can tell which coin they choose.
While your back is turned, have your friends choose one of the coins and
remember the date. Then ask each friend to hold the coin tightly in one
hand for a moment and concentrate hard on the date. When everyone has
had a turn, have the last person drop the coin in the box.
As soon as the coin is returned to the box,
turn around and touch each coin lightly. Four of the coins will be
cool—but the fifth will be warm, because it has taken heat energy from
your friends’ hands. Pretend to think very hard for a moment—and then
surprise everyone by picking out the right coin.
Color up
Does water ever flow up? Yes, it does—and you can prove it to your
friends.
Put three drops of food coloring in one bottle. Fill the bottle with the
hottest water you can get from the faucet. Then fill the other bottle
with cold water.
Place the card over the top of the bottle of cold water. Holding the
card firmly, turn the bottle upside down. Making sure the water doesn’t
spill, place the bottle on top of the bottle of hot water. Line the
bottles up exactly. Then pull out the card.
In a moment a stream of the hot colored water will climb into the bottle
of cold water. Hot water is lighter than cold water. The molecules in
hot water move faster and are farther apart than the molecules in cold
water. So, when the bottles are joined, the hot water pushes upward. It
rises into the heavier, colder water above it.
Materials
bottles (2, large)
card (thin)
food coloring
water
