Force & Movement
Balancing Act Science Magic
Do the impossible balance a can on its bottom rim and amaze your friendsSuitable for kids aged 6+You Need:
What to do:
- Two empty 375ml cans
- 100mls of water approx
- Pour about 100mls of water secretly into one can.
- Have someone try to balance the other empty can on its bottom rim (see picture). It is impossible.
- Then amaze them, by easily balancing your magic can on its bottom rim (they dont need to know it has water in it).
Why is it so?This science trick is so simple, but so much fun. We use it in some of our science incursions and primary children of all ages are amazed by it, especially in the upper grade levels: I love hearing the astonished oohhhs and ahhhhs! It works because the water adds weight to the bottom of the can, changing its centre of gravity and allowing it to balance in impossible ways.
Make an age-old toy: The Cartesian Diver. It floats in a bottle filled with water, but when you squeeze the bottle, the diver mysteriously plunges to the bottom.Suitable for kids aged 5+ with parental supervision.You Need:
What to do:
- An empty soft drink bottle with cap (any size, your diver will dive further in a bigger bottle)
- A third of a straw
- Paper clip
- Small chunk of modelling clay
- Glass or cup to test your diver in
- Fill the bottle with water.
- Make your Cartesian Diver by bending the third of a plastic straw in half. Holding the straw, bend the paper clip so its two U-shapes are separated. Slide one U-shape into each end of the straw to secure it. Mould a small amount of modelling clay or plasticine around the end of the paper clip. You want to completely seal the ends of the straws too, so no water can get into it.
- Fill the glass or cup with water and test your diver. This is the tricky step. You want the diver to barely float upright in the water (with only a small amount of the diver above the surface of the water). Add or remove plasticine to achieve this effect it could take a while! Note: a medicine bottle or plastic pipette will also work as your diver.
- Place the ready Cartesian Diver into the filled bottle of water and screw the lid on tightly. Your diver should be floating on the top, just like in the glass/cup you tested it in.
- Squeeze the bottle gently and watch as your diver plunges to the bottom of the bottle. Release your squeeze and he zips back to the surface. Can you control your diver so it stays at a particular depth? How about adding some food dye to your ocean bottle and perhaps decorating the outside in an ocean theme? Can you think of any other things you could use as your diver?
Why is it so?In the beginning, the diver is buoyant in the water and floats on top because of the trapped air bubble making it light. As you squeeze the bottle and apply pressure, the air bubble in the straw becomes squashed and more dense. Dense air doesnt float as well as air that is more spread out because its heavier, and so the diver sinks. When you stop squeezing and remove the pressure on the air bubble, it spreads out, becomes less dense and the diver shoots back to the top.
Make this rocket quickly and easily out of drinking straws. Then blast it high into the air using air pressure. Fun and completely safe!Suitable for kids aged 5+ with parental supervision.You Need:
What to do:
- A drinking straw (preferably one that bends near the end)
- Half a wider drinking straw (with a large enough diameter to slide easily over the other straw) Note: you can always make one of these out of paper
- Masking tape
- Pinch one end of the wide half-straw and stick a piece of masking tape over it, to seal the end closed. This is your straw rocket.
- Slide your rocket straw over the straight end of the full-sized straw. This narrow full-sized straw is the rockets launching pad.
- Put the launching pad straw in your mouth, and blow hard. Watch your rocket straw blast off high into the air!
- You might like try taping various paper shapes (triangles, squares etc.) or fins to different sections of the rocket and see the effect they have on flight. Does a shorter straw rocket fly better than a longer one? Who can blast their rocket the furthest? Who has the best aim?
Why is it so?This is a classic example of Newtons Third Law of motion in action. According to Newton, for every action there is an equal and opposite reaction. As you blow, air is forced through the launching-pad straw and pushes against sealed rocket-straw at the end. The resulting force causes the rocket-straw to blast high into the air. So much fun!
Egg In A Bottle
This classic science demonstration never ceases to amaze. Get a hard-boiled egg through a small bottle neck opening and into the bottle without touching it. A great way to learn about air pressure.Suitable for kids aged 10+ with parental supervisionCAUTIONThis experiment requires the use of matches and a small flame. Please exercise caution, and only perform under adult supervision.You Need:
What to do:
- A hard-boiled egg with the shell removed
- A glass bottle with a mouth slightly smaller than the egg (fruit-drink bottles work well)
- Small piece of newspaper about 10cm square
- Place the shelled egg on the mouth of the bottle to prove that the egg does not fit through the opening.
- Fold the newspaper into a strip so that it can be easily dropped into the bottle.
- Use the matches to ignite the folded strip of newspaper and remove the egg from the mouth of the bottle. Quickly drop the burning newspaper into the bottle.
- Watch what happens. Within a few minutes the egg should squeeze through the opening and into the bottle. Why?
- If the egg is more than about a centimetre bigger than the opening of the bottle it may break upon entering. To prevent this use a smaller egg, or rub some oil around the mouth of the bottle. A water-filled balloon can be used in place of the egg.
Why is it so?A change in air pressure causes the egg to be pushed into the bottle. The air pressure inside and outside the bottle is the same at the beginning of the experiment. When the burning paper is dropped into the bottle, the air inside heats-up and expands. After the burning newspaper goes out, the air cools and contracts. The air inside the bottle has a lower pressure than the air outside, and the high pressure air outside pushes the egg into the bottle.
Floating Paper Clip
Paper clips sink in water, right!? Using a piece of paper towel and a steady you can get them to float. Its all about the surface tension of the water. Try adding a drop of liquid detergent to upset the balance. Or floating the paper clips in different liquids. Lots of fun!Suitable for kids aged 5+You Need:
What to do:
- Container or bowl of water
- Paper towel
- Paper clips
Photo Credit: AyeKay
- Drop a paper clip in the water, and watch it sink to the bottom. Why does it sink?
- Tear off a piece of paper towel about half the size of a dollar note (size doesnt matter, as long as its bigger than the paper clip).
- Place the piece of paper towel gently on to the water so it floats.
- Carefully place a paper clip on top the piece of paper towel so it, too, floats.
- Wait a few seconds until the paper towel sinks. You may want to give it a helping hand by pushing down on the paper towel with a pencil or your fingers, being careful not to disturb the paper clip.
- Mysteriously your paper clip should now be floating on top of the water. Why did it sink before, but float now?
- Experiment by adding a drop of liquid detergent to the water. How does it affect the floating paper clip? Why? Can you get the paper clip to float in different liquids? Why?
Why is it so?Paper clips sink in water because they are heavier, or more dense than water. Gravity pulls harder on denser objects. The water pushes back up on the paper clip, against gravity, but not with enough force to keep the paper clip afloat.
So how is it possible for the paper clip to float!? With a little thing scientists call surface tension. The surface of water has what is known as surface tension, a bit like a skin. The particles or molecules that make up water are attracted to each other in all directions and, just like good friends, stick tight together. The paper towel helps you lower the paper clips onto the surface of the water without breaking the skin. So the paper clip is not truly floating, it is being held up with the surface tension of the water. Lots of insects, like water striders, use this skin to walk across lakes and streams.
Hairdryer Hover Ball
Hairdryers are not only good for drying hair. Impress your friends and float a ping pong ball in mid-air for minutes.Suitable for kids aged 7+ with parental supervisionCAUTIONThis science activity should only be done under adult supervision as it requires the use of an electrical hairdryer. Ensure the hairdryer is always on its coolest setting.You Need:
What to do:
- Ping pong ball
- Toilet roll, or cardboard tube (optional)
- Pencil (optional)
- Plug the hairdryer in at the wall, and put it on its coolest setting.
- Place the ping pong ball on top, then switch the dryer on. Wow! Watch the ball float and hover in mid-air.
- Try tilting the hairdryer from side-to-side. How far can you turn it before the ball falls?
- With a friends help, try directing the ball through a toilet roll or cardboard tube. Try moving the hairdryer underneath the ball and get it to jump over a stick or pencil. Then try catching the ball on the other side with the hairdryer. Your own mid-air obstacle course! Are you more skill full than your friends?
Why is it so?The stream of air from the hairdryer holds the ball up. But what keeps the ball from falling sideways? Bernoullis Principle, thats what. Believe it or not, but the fast-moving air from the hairdryer has a lower pressure, than the slower moving outside air. When the ping pong ball tries to leave the air stream, the high pressure outside-air pushes the ball back to where it came from. Ultimately resulting in ping pong levitation.
Make your own simple hovercraft out of an old CD and a balloon. Then watch it glide over the floor on a cushion of air. Make a few and have some races with friends which design outperforms them all?Suitable for kids aged 5+ with parental supervisionYou Need:
What to do:
- Old CD (youre not listening too anymore)
- Strong craft glue or super glue
- Pop-top lid from a drink bottle
- Ensuring that the pop-top lid is closed, glue the bottom of the lid to the centre of the CD. The base of the lid needs to be completely covering the hole in the centre of the CD. Allow glue to set and dry.
- Blow up the balloon, and pinch or twist its neck to ensure no air escapes.
- Stretch the neck of the balloon over the closed end of the pop-top lid. Try not to let any air escape in the process.
- Place the CD hovercraft on a smooth, flat surface (balloon side facing-up), and give it a push. How far does it travel?
- Now, open the pop-top lid so the air from the balloon can start to escape, and give the craft a push. How far does it move this time?
- Make a few CD hovercrafts and have some races with friends. Try your craft on different surfaces, which works best? Why? Change the design of your hovercraft slightly by using different materials, or larger balloons. How do these changes effect the performance of your craft?
Why is it so?Air flows out of the pop-top lid when its open, and under the CD. Flowing air creates a kind-of cushion under the CD reducing friction, or rubbing forces. Machine brakes work on the principle of friction to slow things down. Because the CD is weighted and has a very flat surface, air lifts the whole CD off the surface allowing it to glide easily. Air hockey tables work the same way, with a fan under the table pushing air through tiny hole on the tables surface. The flowing air reduces friction and allows the puck to move freely and quickly over the table. And SCORE!
Watch your favourite school snack dance in soda water!Suitable for kids aged 5+You Need:
What to do:
- 10 x Sultanas
- 1 x Litre of Soda Water
- 1 x Transparent Contrainer
- Pour the soda water into the container.
- Gently add the sultanas one at a time to the soda water.
- Watch them float to the surface and then sink down to the bottom.
- How long will this dancing go on, and why?
Why is it so?How are they dancing? Well soda water contains a large amount of dissolved carbon dioxide. That's the stuff that makes it fizzy and fun to drink! The bubbles are less dense that soda water, so they rise to the surface. The sultanas initially sink to the bottom as they are heavier than water, but as the bubbles start to rise to the surface, they wedge themselves into the crevices of the sultanas, providing a buoyant force to help threm rise to the surface!
But they won't float on the surface for ever! Once the sultanas reach the surface, the bubbles supporting them pop! Causing them to sink again. But they will rise again as new bubbles lift them up! Will this rising and sinking motion go on forever?
No it won't. The rising and sinking motion will stop once all the carbon dioxide has escaped (soda goes flat). You will also notice that with time the dried sultanas will have absorbed some water and become too heavy to rise. You will also notice that the sultana will expand and cause its skin to become smooth, leaving no crevices for the bubbles to wedge between.
Instead of using soda water you could create a bubbly liquid by mixing vinegar and baking soda, or experiment with other objects that can dance too!Do more cool experiments with the science kits available on this website.