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Welcome to Science for Kids!!
We encourage your interest in all things
scientific. We've described some of the things we do in our
school science assemblies that are safe for you to try. Please be
sure to get adult help from your family or teachers before trying
any of these, and be sure to follow proper safety
procedures, including wearing safety glasses, when trying any of
these science demonstrations.
Pop Can Collapse
Description
A can is collapsed by atmospheric pressure and nothing else!!
Materials
Procedure
Pour two teaspoons of water into an empty pop can. Boil the water by
putting the can on a hot plate or over a candle. When steam begins
to leave the can, using gloves or tongs, turn it over quickly so the
hole is "down" and plunge it into the bowl of cold water. The steam
will condense, leaving a partial vacuum within the can. The can will
collapse rapidly due to air pressure pushing on the sides of the
can.
Theory
As the water inside the can turns to steam, the steam pushes the air
out of the can. When the can is plunged into cold water, the steam
condenses back into water, resulting in a partial vacuum inside the
can. With little or no air in the can, equilibrium is lost and
14.7 pounds per square inch of atmospheric pressure presses on the
can, causing it to collapse.
Atmospheric Pressure Resistance
Devices
Description
Two plungers are held together by atmospheric pressure only
Materials
Procedure
Push the plunger cups together so that most of the trapped air
is pushed out (be sure the rims of the cups are clean and dry to
assure a tight seal). It will be very difficult or impossible to
separate the plungers simply by having someone pull on each plunger
handle.
Theory
The area inside the two plunger cups is no longer at equilibrium (at
the same pressure) with the atmospheric
pressure that is pushing on the outsides of the two plunger cups. Depending on the size of the plunger cups, and with
14.7 pounds per square inch of atmospheric pressure pressing on each
plunger cup, it may require 400 to 600 pounds of pulling force to
separate them! However, by simply separating a small area of the two
plunger cup rims (perhaps with a finger nail or by sliding them
across each other) air will rush into the plunger cups, returning
them to equilibrium and allowing them to be easily separated.
Pocket Rockets
Description
A film canister is launched using carbon dioxide to propel it.
Materials
Procedure
Put a level teaspoon of baking powder (not baking soda) in a film
canister. The canister has to be one of the white plastic canisters
from Fuji Film, not the black ones with the gray lid. To the baking
powder add one quarter film canister of water and quickly place the
lid on the canister. Shake well and place it lid end down on a flat
surface. After a few seconds the canister will be blown into the
air, leaving behind a splatter pattern similar to that seen on
launch pads when rockets blast off. This is best done outdoors or in
a room with a smooth floor and a high ceiling (like a gymnasium).
Theory
The chemical reaction between the water and baking powder causes
carbon dioxide to form, which builds up enough pressure to “pop” the
lid from the film canister and cause it to shoot into the air. Baking powder is a solid mixture that is used as a chemical
leavening agent in baked goods. It can be composed of a number of
materials, but usually contains baking soda (sodium bicarbonate, a base), cream of tartar (potassium bitartrate, an acid),
and cornstarch (an inert filler). When you
add water to baking powder, the dry acid and base go into solution
and start reacting to produce carbon dioxide bubbles.
Baking soda, has the chemical formula NaHCO3. Cream of tartar has the formula KHC4H4O6. Carbon
dioxide has the formula CO2. The chemical reaction when water is added to baking
powder is:
NaHCO3 + KHC4H4O6 ----> KNaC4H4O6 + H2O +
CO2
Gas Bags
Description
A chemical reaction between two solids creates a gas to fill up
a plastic bag. This experiment also illustrates the three states
of matter all in one bag: we add a liquid (1) to some solids (2) to
create a gas (3).
Materials
-
One gallon size Ziplock bag
-
5 teaspoons of baking soda
-
5 teaspoons of calcium chloride
(in some brands of "ice melt", not all - check the ingredients)
-
6 teaspoons water
Procedure
Put the baking soda and the calcium chloride into the Ziplock
bag. Add the water and seal the bag. Move the bag around in your
fingers to mix the materials together. You should hear a fizzing
noise, and the bag will fill up with carbon dioxide gas.
Theory
A chemical reaction occurs between the calcium chloride and the baking
soda in which a double replacement reaction takes place. The two
solids switch partners and form a new substance--the precipitate
calcium carbonate. As the precipitate is formed, the bicarbonate
breaks down first to make hydrogen ions, an acid. This acid then
converts some of the bicarbonate to carbon dioxide gas which begins
to blow up the plastic bag. You will usually notice a warm spot on
the bag - this is where there is still a lot of calcium chloride,
which gets warm from an exothermic reaction (a reaction which
releases energy, in this case, in the form of heat).
If the two solid materials are
placed in separate corners of the bag without any mixing, when the
water is added, as part of the chemical reaction between the two
solids, a change in temperature can be felt--in one corner of the
bag, an exothermic reaction causes the calcium chloride gets warm,
while in the other corner an endothermic reaction makes the baking
soda gets cold.
Calcium chloride + baking soda
(sodium bicarbonate) = calcium carbonate + sodium chloride +
hydrogen ions
CaCl2 + 2 NaHCO3 ---> CaCO3 + 2 NaCl + H+ ions
Hydrogen ions + sodium bicarbonate
---> carbon dioxide + water + sodium ions
H+ ions + NaHCO3 ---> CO2 + H2O + Na+
Egg in the Bottle
Description
A large hard boiled egg in pushed through the smaller neck of a
bottle by air pressure only.
Materials
-
A large hard boiled
egg, peeled
-
A bottle with a neck
slightly smaller in diameter than the egg (we use an apple juice
bottle)
-
Strip of newspaper
(method 1 only)
-
lighter (method 1
only)
Procedure
Method 1: Using the lighter, set a narrow strip of
newspaper paper on fire and quickly drop it into the bottle. Set the
egg on top of the bottle (small side pointed downward). When the
flame goes out, the egg will get pushed into the bottle.
Method 2: Set the egg on the bottle. Run the bottle under
very hot tap water. Warmed air will escape around the egg. Set the
bottle on the counter. As it cools, the egg will be pushed into the
bottle. (do NOT place the bottle in a pot of boiling water or heat
the bottle on a stove or in a microwave, as this may cause the
bottle to shatter)
Method 3: Set the egg on the bottle. Immerse the bottle in
ice water. The egg is pushed in as the air inside the bottle is
chilled.
Theory
If you just set the egg on the bottle, its diameter is too
large for it to slip inside. The pressure of the air inside and
outside of the bottle is the same (at equilibrium), so the only
force that would cause the egg to enter the bottle is gravity.
Gravity isn't sufficient to pull the egg inside the bottle.
When you change the temperature of the air inside the bottle, you
change the pressure of the air inside the bottle. If you have a
constant volume of air and heat it, the pressure of the air
increases. If you cool the air, the pressure decreases. If you can
lower the pressure inside the bottle enough, the air pressure
outside the bottle will push the egg into the container.
It's easy to see how the pressure changes when you chill the
bottle, but why is the egg pushed into the bottle when heat is
applied? When you drop burning paper into the bottle, the paper will
burn until the oxygen is consumed (or the paper is consumed,
whichever comes first). Combustion heats the air in the bottle,
increasing the air pressure. The heated air pushes the egg out of
the way, making it appear to jump on the mouth of the bottle. As the
air cools, the egg settles down and seals the mouth of the bottle.
Now there is less air in the bottle than when you started, so it
exerts less pressure. When the temperature inside and outside the
bottle is the same, there is enough positive pressure outside the
bottle to push the egg inside.
Heating the bottle under hot tap water produces the same result
(and may be easier to do if you can't keep the paper burning long
enough to put the egg on the bottle). The bottle and the air are
heated. Hot air escapes from the bottle until the pressure both
inside and outside the bottle is the same. As the bottle and air
inside continue to cool, a pressure gradient builds, so the egg is
pushed into the bottle.
How to Get the Egg Out
You can get the egg out by increasing the pressure inside the bottle
so that it is higher than the pressure of the air outside of the
bottle. Roll the egg around so it is situated with the small end
resting in the mouth of the bottle. Tilt the bottle just enough so
you can blow air inside the bottle. Roll the egg over the opening
before you take your mouth away. Hold the bottle upside down and
watch the egg 'fall' out of the bottle. Alternatively, you can apply
negative pressure to the bottle by sucking the air out, but then you
risk choking on an egg, so that's not a good plan.
Hovercraft
We made our hovercraft currently used in our Aurora program following these
plans by William J Beaty.
Click on this link: http://amasci.com/amateur/hovercft.html
Levitating Spheres
(Bernoulli Balls)
Description
A ball is levitated (floats in the air) with a stream of air.
Materials
Procedure
Turn on the hair dryer (on "cool air" if it has that setting)
and aim it straight up. Place the ping pong ball in the center of
the air stream and let it go. It should rise up and stay in the
center of the air stream, seemingly levitating!!
Theory
In 1738, the Swiss mathematician Bernoulli observed that
when air moves faster the pressure decreases.
Bernoulli's principle
tells us that air that is moving at high speed has lower pressure
than still air. The air moves around the ball to create a pocket of
low pressure air. When the ball moves to the side of the low
pressure pocket, it will be pushed back in by the higher pressure of
the still air outside of the pocket. The upward force from the air
stream keeps the ball aloft. It's a very cool effect!
Fun Variations
With a stronger air stream (a leaf blower or shop vacuum), you
can levitate larger things such as beach balls, or even plastic pop
bottles (empty, of course). So how far you can angle the air stream
before the ball falls. Try levitating two or more balls together.
You are encouraged to experiment, but always have adult help and be
careful!!
Measuring
Carbon Dioxide in Soda Pop
Description
The carbon dioxide from a bottle of soda pop is captured and
measured.
Materials
-
An unopened 1 liter
bottle of soda pop - any type or brand
-
A glass measuring cup,
2 cup capacity
-
A large bowl about 1/4
full of water
-
A plastic tube or
piece of aquarium tubing, about 18 inches long
-
clay or glue
-
a second bottle cap
from a different 1 liter bottle of soda pop
Procedure
Fill the glass measuring cup with water, cover it with
an index card or other stiff card and then turn it upside down into
the large bowl of water making sure that none of the water in the 2
cup measure escapes. Drill a hole into the top of the second bottle
cap (ask for help from an adult) and put one end of the aquarium
tube into the hole. Seal the area around the hole with clay or glue.
Now you are ready. Remove the cap from the unopened liter of soda
pop and quickly replace it with the modified cap/tube assembly.
Place the other end of the tube into the over turned 2 cup measure
in the bowl. You need to do this very quickly so that you minimize
the amount of CO2 you loose when you open the bottle. Then just let
it sit. As the CO2 comes out of solution in the bottle it will push
the water out of the 2 cup measure in the bowl. As this happens,
you can see how much CO2 is in the bottle. To get all of the gas
out, you will need to gently shake the bottle every few
minutes to begin with and then every so often through out the day.
It will take 24 to 30 hours for all of the carbon dioxide to escape
from the soda pop.
Theory
The fizzing bubbles in soda pop are
called "carbonation" and come from carbonic acid, which breaks down
into carbon dioxide gas (CO2)
and water. It is the carbon dioxide gas that is
responsible for the fizziness. Carbonic acid is added at the
bottling plant just before the bottles are filled with the soda pop.
When this occurs, the soda flows into the bottle under pressure and
is capped before the carbonation can escape. The empty space at the
top of the container is therefore filled with carbon dioxide gas
that is at a higher pressure than atmospheric pressure. Soda pop can
only hold so much dissolved CO2 and the carbon dioxide at the top of
the container prevents any of the dissolved carbon dioxide from
escaping from the soda pop. As soon as you open the cap, the
CO2 which is at a higher pressure begins to escape into the
atmosphere which is at a lower pressure, causing the hissing noise
you hear when you open the container. This release of pressure
inside the container allows the dissolved CO2 to begin rising and
bubbling up out of the soda pop and into the atmosphere.
When a partially emptied bottle is recapped, more space is available
for carbon dioxide gas to escape from the soda pop, and the
remaining liquid in the bottle become more flat. Because pressure
cannot build up above an open bottle or cup, the soda in it will
soon go completely flat. In our science assemblies, we speed up the
process by shaking the bottle, causing the carbon monoxide gas
molecules to expand more quickly and force some of the soda pop out
of the bottle. We only use club soda because it does not have
any sweetener in it and is not sticky.
Combustion
We DO NOT recommend any combustion
experiments for elementary school children to try. However, the
theory is important to learn. Ignition can be described as a process
leading to combustion (fire), and occurs when a sufficiently high
source of energy (such as an open flame, high heat source or
electrical spark) is provided to enable the reaction between a fuel
(something that burns) and oxygen to take place. Combustion can only
occur if the material involved is capable of being ignited (i.e.
combustible). For combustion to take place, three things are
required:
- FUEL: This is a substance that is capable of burning
(solids, liquids or gases);
- HEAT: This is the energy or source of ignition, which will
enable the reaction to start, such as fire or a spark;
- OXYGEN: This reacts with the fuel causing “new” substances
to be produced (combustion products) - oxygen usually is from the
atmosphere, but may be provided separately (rockets that leave the
atmosphere bring their own liquid oxygen in a fuel tank). |
