Windbags!
CHALLENGE
Here's the challenge... How many breaths will it take to blow up a nearly 2 meter long bag?
Using physics you can do it in 1!
THING YOU NEED:
 Long plastic bags
EXPERIMENT:
1. Invite a child to blow up the bag, keeping track of the number of breaths it takes.
Then, let all of the air out of the bag. Explain to the children that you can blow up the
bag in one breath!
2. Have someone assist you by holding onto the closed end of the bag. Hold the open end
of the bag approximately 30 cm away from your mouth. Using only one breath, blow
as hard as you can into the bag.
***Remember to stay about 30 cm away from the bag when you blow***
3. Quickly seal the bag with your hand so that none of the air escapes.
HOW DOES IT WORK?
The long bag quickly inflates because air from the atmosphere is drawn into the bag from the
sides along with the stream of air from your lungs.
In 1738, Daniel Bernoulli observed that a fast moving stream of air is surrounded by an area
of low atmospheric pressure. In fact, the faster the stream of air moves, the more the air
pressure drops around the moving air. When you blow into the bag, higher pressure air in the
atmosphere forces its way into the area of low pressure created by the stream of air from
your lungs. In other words, air in the atmosphere is drawn into the long bag at the same time
that you are blowing into the bag.
HOW IS IT USED?
Firefighters use Bernoulli's principle to quickly and efficiently force smoke out of a building.
Instead of placing the fans up against the doorway or window, a small space is left between
the opening and the fan in order to force a greater amount of air into the building.
Firefighters call this "Positive Air Flow."
Anti-Gravity Jars!
DEMONSTRATIO
N
Fill the glass jar with water and cover it with a card. As you turn the whole thing upside
down over someone’s head, the audience can hardly contain themselves. Just as they
thought, no water spills out because the card magically sticks to the mouth of the upside
down jar. But what happens when you remove the card!?
THING YOU NEED:
 Kilner Jars with netting over the top
 ‘DO NOT REMOVE’ Card
 Water
EXPERIMENT:
1. Fill a jar with some water (ideally in front of the children).
2. Ask for a volunteer (explain they may get a bit wet!)
3. Place the ‘DO NOT REMOVE’ card on top of the Kilner Jar, holding it carefully in
place invert the jar with the card over the person’s head.
4. Pose the question, “What would happen if I let go of the card?” Carefully let go of the
card – it should stick to the Kilner Jar.
5. Explain that the air pressure in the room is stronger than the weight of the water and it
is pushing the card up against the jar.
6. Explain that ‘obviously’ if the card was removed the water would fall out. As you
explain this slowly remove the card! Magically the water stays in the jar!!
***Please note a small amount of water may fall on the person***
HOW DOES IT WORK?
Air Pressure: The atmosphere exerts pressure on everything in it. Because it's a gas, air not
only pushes down, but also upwards and sideways. The card remains in place because the
pressure of the air molecules pushing up on the card is greater than the weight of the water
pushing down.
Surface Tension: The surface of a liquid behaves as if it has a thin membrane stretched over
it. A force called cohesion, which is the attraction of similar molecules to each other, causes
this effect. The surface tension "membrane" is always trying to contract, which explains why
falling droplets of water are ball shaped. The water stays in the jar even though the card is
removed because the molecules of water are joined together (through cohesion) in the small
gaps in the mesh.
HOW IS IT USED?
Water Boatmen and other insects use the principle of water tension to float on top of ponds.
It is also used in making different materials waterproof as if they material can maintain the
water tension water will roll over the material instead of going through it.
Invincible Balloons!
DEMONSTRATIO
N
Balloons and skewers don’t mix – do they? But by understanding polymers there is no
problem.
THING YOU NEED:
 Balloons
 Skewers
 Oil
 Sharpie
EXPERIMENT:
1. Inflate the balloon until it’s nearly full size and then let about a third of the air out. Tie
a knot in the end of the balloon.
2. Pose the question of what will happen of we try and push the skewer through the
balloon.
3. Dip the tip of the wooden skewer into the cooking oil, which works as a lubricant.
4. Place the sharpened tip of the skewer on the thick end of the balloon where you blow
it up and gently push the skewer into the balloon.
5. Push the skewer all the way through the balloon until the tip of the skewer touches the
opposite end of the balloon, look for the thickest part and keep pushing until the
skewer pierces the other side of the balloon.
6. Gently remove the skewer from the balloon. Of course, the air will leak out of the
balloon, but the balloon won’t pop.
HOW DOES IT WORK?
To explain how it works you can repeat the experiment but before blowing up the balloon
draw large (similar sized) dots on the balloon all over it. When you blow the balloon up and
then let out some air again you will see that the dots are all different sizes. What is
happening is that the rubber is made up of long strands of rubber called polymers. When the
balloon is inflated it stretches these polymers, but not all the polymers are under the same
about of pressure. At the ends of the balloons there are slightly thicker amounts of rubber (so
more polymers) and because of the shape of the balloon they are under less stretching stress.
By pushing the skewer through these low stress areas, the polymers are able to stretch
around the skewer and not rip apart.
HOW IS IT USED?
Materials made up of long strands are called polymers and they are around us in many
different forms. Their construction gives them strength, flexibility, durability and they are
fairly easy to produce. Here is a list of some:
Polythene - bags, especially shopping bags/carrier bags; Polystyrene - packaging (the white
balls in packing are polystyrene); Teflon - the non-stick surface on frying pans; Polyester and
nylon – clothes; Kevlar - used in bulletproof jackets, and found in bicycle tyres.
Cloud Generator!
DEMONSTRATIO
N
How clouds are formed and how air pollution creates more clouds all with a humble bottle!
THING YOU NEED:
 Empty cola bottle with cap
 Small amount of water
 Matches
EXPERIMENT:
1. Explain we are going to show how pollution makes clouds by squeezing the bottle.
2. Place a couple of capfuls of water in the bottle and shake – explaining that clouds are
made of water
3. Put the lid on and get someone to try squeezing the ‘clean’ bottle – it shouldn’t work.
4. Add some pollution by lighting a match, letting it burn quite a bit, blow it out then
catch the smoke in the bottle by squeezing the bottle and sucking the smoke in – put
the lid back on.
5. Now get someone to squeeze the bottle again – when they release the cloud should be
created.
HOW DOES IT WORK?
Even though we don't see them, water molecules are in the air all around us. These airborne
water molecules are called water vapour. When the molecules are bouncing around in the
atmosphere, they don't normally stick together.
Squeezing the bottle forces the molecules to squeeze together or compress. Releasing the
pressure allows the air to expand, and in doing so, the temperature of the air becomes cooler.
This cooling process allows the molecules to stick together - or condense - more easily,
forming tiny droplets. Clouds are nothing more than groups of tiny water droplets!
This is noted in physics by the Gas Laws which look at how pressure, volume and
temperature are all linked with gases. Usually though we would need to exert a large amount
of pressure to do this. The smoke adds dust to the formula which allows the water to stick,
creating the cloud without large pressure.
HOW IS IT USED?
This experiment shows how pollution in the air can cause greater cloud formation and this
poses issues with our environment. It also shows how pressure, volume and temperature are
linked with gasses and understanding these links is needed in filling containers with gas. It
also explains how when you spray compressed gas the can gets cold and condensation forms
on the outside.
Water Bottle Tornado
Challenge!
CHALLENGE
How can you use the science of tornadoes to empty a bottle full of water?
THING YOU NEED:
 Large bottles
 Water
 Outside space to pour the water away on.
EXPERIMENT:
1. Fill the bottles with water and ask a child to turn one over to pour the water out.
2. How can we to empty the water faster?
3. To empty it the fastest turn it over and start to swirl the bottle in a circular motion
making the circles tighter and faster – this will create a ‘tornado’ in the water and it
will pour out.
HOW DOES IT WORK?
Swirling the water in the bottle while pouring it out causes the formation of a vortex. The
vortex looks like a tornado in the bottle. The formation of the vortex makes it easier for air to
come into the bottle and allows the water to pour out faster. If you look carefully, you will be
able to see the hole in the middle of the vortex that allows the air to come up inside the
bottle. If you do not swirl the water and just allow it to flow out on its own, then the air and
water have to essentially take turns passing through the mouth of the bottle.
HOW IS IT USED?
The vortex not only allows the air to move it actually sucks the air into the bottle. They use
this idea in vacuums such as a Dyson where the air is made so swirl and create a vortex
sucking more air in. It is also the principle used in jet engines to make them more powerful
and more efficient.
Pop Rockets!
CHALLENGE
How high can you make the pots fly? This simple little experiment is a favourite of mine as
it is in fact hugely complex as multiple aspects of chemistry and physics can be
demonstrated by changing the variables!
THING YOU NEED:
 Film Canisters
 Alka-Seltzer – THESE CONTAIN ASPRIN DO NOT ALLOW THE CHILDREN
TO INGEST THEM OR THE SOLUTION CREATED
 Water
 Outside space to launch rockets.
 Paper and scissors to make a cone for the top. (optional)
EXPERIMENT:
1. To launch a rocket take a canister, pour a capful of water into it.
2. Quickly - add half an Alka-Seltzer, put the cap on and place it cap down on the floor
and back away.
3. It will go pop after approximately 10 seconds.
4. How can you make the rockets go higher? – make them more aerodynamic? Change
the amount of water or Alka-Seltzer? Try adding warm water?
HOW DOES IT WORK?
When the Alka-Seltzer hits the water it dissolves and the ingredients mix. This includes
sodium bicarbonate (a base) and citric acid (an acid). When a base comes in contact with an
acid it will neutralise it so it is no longer acidic. In this case the two mix to become sodium
citrate, some water and importantly for this experiment carbon dioxide gas! The gas builds
up in the canister until the lid cannot contain it and… POP!
HOW IS IT USED?
This experiment shows how new chemicals can be created in a chemical reaction – i.e. the
carbon dioxide gas is created from the base neutralising the acid in the Alka-Seltzer. It also
shows how the pressure is exerted to create a force. If you play with the water level you will
see that the more water that is added the less force is created. This shows the principle that
liquids are non-compressible and therefore there is a smaller area for the carbon dioxide gas
to compress into compared to having a small amount of water. Also if you added warm water
it should have created a bigger reaction showing that this is an endothermic reactions (the
reaction absorbs energy from its surroundings in the form of heat) and due to the added heat
it was able to react faster and compress the gas faster. Not to mention the aspects of
aerodynamics if that has been explored!