This fun science trick demonstrates that hot and cold water have different densities.
The demonstration reminded my kids that lower density liquids float above higher density liquids. They learned that hot water molecules move faster and further apart from each other than cold water molecules.
The trick also allowed us to revisit the topic of surface tension and to build on the air pressure science we learned last term.
What you need
2 identical jars or drinking glasses (eg babyfood or salsa jars)
hot and cold water
red and blue food colouring
index cards or similar
scissors
a large shallow dish to catch spills
What you do
1. Cut a square of card big enough to completely cover the mouth of a jar.
2. Fill one jar with cold water. Add a drop of blue colouring and stand the jar in the baking pan.
2. Fill the second jar with very hot water. Add a drop of red colouring.
3. Slowly add more hot water to the red jar until you see a bulge of water over the rim. (Take the opportunity to talk about surface tension here.)
4. Lay the square of card on top of the jar of hot water and tap it gently.
6. Put the upside-down red jar on top of the blue jar. Ask your students to predict what will happen when you slowly pull out the card, then do so.
Atmospheric pressure holds the card and water in place (left)
What happens
When you remove the card between the two jars, the hot red water stays in its jar on top and the cold blue water stays on the bottom.
Hot water floating on top of cold water
Reverse the jars
7. Repeat the experiment the other way round. Turn the jar of cold water upside-down and put it on top of the hot water jar. Again, ask students to predict what will happen when you remove the card.
What happens
When you remove the card, the water quickly turns purple, as the cold and hot water mix together.
Hot and cold water mix
The scientific explanation
When water is heated, the water molecules move faster. They bounce off one another and move further apart. The extra space between the molecules means the same volume of water weights slightly less and is less dense than cold water.
When we put the hot water on top, the less dense hot water floats on top of the denser cold water. The red water and blue water stay in their respective jars and do not mix.
When we put the cold jar on top, the more dense cold water immediately sinks to the bottom and the two colours mix.
We talked about a previous demonstration in which we created a column of liquids with different densities, and reminded ourselves by pouring water into a glass of oil and watching the oil float to the surface.
They heated the salt solution in a saucepan, capturing the evaporated water on the oversized lid. The condensed water was then collected as it dripped off the lid.
Separating water and salt
I hadn’t been sure how C(9) and J(8) would get on with this activity. I knew they’d enjoy it, but I thought I might have to help them more than I did.
Seeing how they confidently and intelligently tackled the puzzle reassured me that our science un-curriculum is still working well.
This hands-on hydraulics experiment is a fun way to investigate the power of liquids.
We used hydraulic power to create a simple machine which our Lego mini figs – and all the family – had fun playing with.
Our hydraulic theme-park even inspired a movie!
A liquid under pressure can apply a lot of force and this can be used by machinery to do work. Using liquids like this is a branch of engineering called hydraulics.
{I’ve added a steps 1 and 2 to the instructions given in Science Experiments for Kids, to give you the benefit of our mistakes.}
1. Stretch the balloon by blowing it up and letting the air out again.
2. Attach the tubing to the empty balloon and seal the join with tape. Check the join is water-tight by attaching the funnel to the other end of the tube and filling with water. Remove the funnel and drain out the water.
3. Cut the empty bottle so that it is just a little taller than the can. (We should have cut a bit more off ours.) Use a pencil to make a small hole near the bottom of the bottle.
4. Feed the free end of the pipe through the hole in the bottle, leaving the balloon inside.
5. Put the heavy book on top of the bottle.
6. Attach the funnel to the pipe and fill with water. (Hold the funnel up high to quickly release any air bubbles.)
What happens
The water-filled balloon lifts the can, which in turn lifts the book.
The balloon feels very firm.
The scientific explanation
The weight of the water in the funnel creates enough pressure to force water into the balloon. This force is in turn transmitted through the balloon to lift the book.
Fluids transmit forces more effectively than gases because they can’t be compressed, even under pressure.
Hands-on hydraulics fun
We wanted to apply what we’d learned to create something like this very cool hydraulic elevator.
Unfortunately we couldn’t get our syringes and pipes sealed tightly enough to make it work.
Instead, C(9) had the idea of using hydraulic pressure to create a fun ride for Lego mini figures.
First of all C(9) made a hydraulic see-saw …… which turned into a “Blue Sky Bouncer” theme park ride which had the mini figs queuing up for turnsC(9) even made a movie trailer promoting her ride using iMovie on her iPad
Real life hydraulics
Liquids are used in many kinds of machines to carry force through pipes.
Most of us rely on hydraulic machines every day, for example when we apply the brakes in our cars or fill them with petrol, and even when we run the dishwasher.
Hydraulics is used to design piping systems, pumps, propellers, water turbines, hydraulic presses, and flow-measuring devices.
We enjoyed dipping our toes into hydraulic principles.
There are lots more hydraulics experiments I hope we’ll do in the future. They’re a great hands-on way to learn about the laws of physics, such as Pascal’s Principle.
We’ve wanted to try a hovercraft experiment since we saw a really cool leaf blower hovercraft (like this one) at a science show last year. As we don’t have access to a leaf blower, we used balloon-power!
There are many variations on this experiment. We tried quite a few. I’ll start with the one that worked best and then show you some of the others. (Maybe you’ll have better luck with them.)
What you need
* old CD
* hot glue gun
* sports cap from a water bottle (the kind that you pull up to drink and push down to close)
* push pin (drawing pin)
* large balloon
* a big smooth surface
What you do
1. Use the push pin to make two holes in the cap near the centre.
2. Spread a thin layer of hot glue around the base of the bottle cap and attach it to the CD, over the hole. Give the cap a slight twist as you stick it to ensure an airtight seal.
3. Make sure the cap is down (closed).
4. Blow up your balloon and pinch its neck while you attach it to the top part of the cap. (Easiest with two people.)
5. Place your hovercraft on a smooth flat surface. Give it a push and see what happens {not much}.
6. Now, without removing the balloon, pull up and open the cap. Quickly give the hovercraft a push and watch it continue moving. Push your hovercraft back and forth across a flat surface to keep it moving until the balloon is fully deflated.
Notes: (1) I’ve since seen the experiment set up this way in Science Experiments, but without the pushpin holes
(2) I’ve also seen a version that uses sticky tack (Blue Tack) instead of hot glue
Playing with our hovercraft
The scientific explanation
When you push the hovercraft when the cap is closed (stage 5 above) , friction between the CD and the surface soon stops it moving.
But when you open the cap, air escaping from the balloon cushions the hovercraft. The hovercraft continues moving much farther.
Variations that didn’t work for us {but it’s good to experiment}
1. First we tried making Science Bob’s hovercraft. This involved taping over the CD hole and making six push pin holes in it. No holes were in the lid.
Verdict: A complete dud! I’m not sure what we did wrong, but this hovercraft didn’t do much for us.
Science Bob’s hovercraft
2. The version that eventually worked for us was from Steve Spangler Science. But Steve Spangler suggests making a cardboard collar for the hovercraft.
Hovercraft with collar
Verdict: We made a collar and the hovercraft worked fine, but it was very fiddly trying to get everything attached and the cap open. We eventually removed the collar in frustration, and found that the hovercraft worked just as well without it.
3. We tried making a hovercraft just using a paper plate and balloon.
Paper plate hovercraft
Verdict: Another dud! Perhaps we didn’t make our centre hole big enough?
We found a few other uses for it though!
Hovercraft History
The first modern hovercraft was designed in the 1950’s by Englishman Sir Christopher Cockerel. It crossed the English Channel between Dover, England and Calais, France in two hours.
Until the year 2000, passengers could travel from England to France by hovercraft in just 35 minutes. Passenger hovercrafts still operate between Southsea, England, and the Isle of Wight.
Southsea to Ryde passenger hovercraft {by Barry Skeates}
Hovercrafts are a type of seaplane, and they require large amounts of expensive aviation fuel to keep their giant air-cushions inflated. This is one of the reasons large hovercrafts are less commonly used nowadays.
Military Hovercrafts
Because hovercrafts are able to cross any flat terrain, including water, marshland, tarmac and sand, they are still commonly used for military purposes.
The biggest hovercraft in the world – the Zubr – recently made the news when it landed on a Russian beach filled with hundreds of sunbathers. A Russian defence spokesman reportedly commented, “What people were doing at the beach on the territory of a military base is unclear.” Okay, then!
This week we decided to extend our gummy bear science lab see what happens when you leave them for a bit longer.
J(8) wondered if the same would happen with jelly babies (a popular British sweet, a bit like gummy bears but with a harder outside).
Supplies
Gummy bears
Jelly babies
Water
Glass or jar
Refrigerator, if you want to taste test
What we did
We placed our gummy bears and jelly babies in separate glasses of water and left them for a week (but twenty-four hours would do). We put them in the fridge, to minimise bacterial growth, in anticipation of a taste test.
What happened
We used our senses to examine our gummy bears and jelly babies.
We could SEE that the gummy bears had become three or four times bigger and become more translucent
They FELT “squidgy” and “gooey”
They didn’t TASTE good at all!The jelly babies also expanded… but their hard outside layer split
Gummy bear science
Gummy bears and jelly babies contain water with lots of other things dissolved in a concentrated solution.
The water in the glass flows through the gummy bear’s semi-permeable membranes. This flow (diffusion) of water from a region of low concentration of solute to a high concentration is called osmosis.
The sweets became more translucent partly because the colouring had to go further in the larger sweet, and maybe partly because some of the colouring dissolved in the water.
We were intrigued by some of the gummy bear (right) and jelly baby (left) ingredients
In the case of the jelly baby, we hypothesised that although water can pass through the (sugar?) shell, the outside of the jelly baby is unable to absorb water as fast as the inside, causing it to crack.
More fun with osmosis and jelly babies
We also came across this exciting jelly baby oxidisation experiment – screaming jelly babies. Sadly not one to try at home!
And as for osmosis, I can’t believe we’ve been homeschooling for three years and we’ve never done the celery or carnation experiments?! Guess what we’ll be trying next…
Following our free-style potions session, this week we played with dissolving solids in water. Our focus this time was on exploring rather than scientific accuracy – I wanted the kids’ imaginations and curiosity to be sparked.
Set up
* bowls containing a variety of solids, including instant coffee, gravy granules, salt, caster sugar, sand, flour, sprinkles (two types) and gummy bears (guaranteed to elicit interest)
* large jug of hot water
* large jug of cold water
* glass jars & glasses
* teaspoons
I also printed off a chart for C(9) and J(8) to record their results if they wanted to.
What we did
Before I gave them the chart, I invited the children to use their senses to guess what each of the substances was. The gravy granules evoked a lot of interest here, the smell reminding them of their favourite snacks. (I wonder if they’ll be more excited next time I serve gravy.)
We talked about the scientific method and I suggested that before they added each substance to water, they make a guess which they needn’t share out loud as to whether or not it would dissolve. (The secret hypothesis is a safeguard against my perfectionist child melting down mid-experiment.)
They then took turns putting a teaspoon of each substance into water (first cold then hot), observing, stirring and then recording their results.
Highlights
* The sprinkles were interesting. First they lost their colour, turning the water cloudy. Then after a few minutes they dissolved. C(9) guessed that the colouring was very soluble, and that the sprinkles were made of sugar so also dissolved, but more slowly.
* They loved watching the coffee granules dissolve rapidly in the hot water.
* The gummy bears prompted a couple of spin-off experiments of their own. Firstly the children noticed that they gave off little flecks in the hot water. Then they observed that after being in water for a while, they lost the colour around their edges and expanded slightly, so it was decided to leave them overnight. (I put them in the fridge, anticipating a future taste-test request.) More on this in a separate post.
* They liked watching the gravy vortex created by rapid stirring.
What we might do differently next time
* Both children added every substance to both hot and cold water, which involved a lot of me running around washing out jars. Next time I would suggest they take turns doing the hot or cold water. Or have more jars.
* More importantly, while I was busy washing up jars, the children decided salt wasn’t soluble! They hadn’t given it enough time to dissolve. We repeated this part of the experiment later and talked about how we don’t see and feel bits of salt around us when we swim in the sea!
* I might provide a measuring beaker and spoon, so they could use the same amounts of solid and water each time. We could time how long the solids take to dissolve in hot water compared with cold.
The science
When a solid dissolves, it breaks into tiny pieces, so small that you can’t see them in the water. We call the mixture of solid and water a “solution”. Solutions may be coloured (like coffee), but they are always transparent.
We also talked about how hot water molecules move more quickly so come into contact with solid particles more often, which is why solids dissolve more quickly in hot water than cold.
What next?
Over our next few “potions” session we’ll be experimenting with ways of separating mixtures and solutions.
I’ve been wanting to set up a free-style “potions” invitation for my kids ever since I came across 10 More Magic Potions.
Since we gave up following a science curriculum we’ve played with density, slime, fizzy fountains, elephant’s toothpaste and red cabbage indicator among other things. But, perhaps because we didn’t homeschool from the start, I’ve never set things up quite this way before, and I wanted to give C(9) and J(8) a serious chance to play before we move on to any more specific “potions” experiments (dissolving, separating liquids etc).
A visit on Wednesday to Professor Snape’s potions classroom at the Harry Potter Warner Bros Studios was just the catalyst I needed!
Professor Snape’s Potions Classroom
Here’s what I set out:
Equipment
* test tubes (large and small)
* plastic bowls
* funnels
* coffee filter papers
* sieves
* whisks
* long-handled spoons
* popsicle sticks
* measuring beakers
* pipettes, eye droppers & a medicine syringe
* conical flasks
* lab glasses
“Ingredients”
* bottles of coloured water
* plain water
* bubble mixture
* cornflour
* salt
* sand
* mustard powder
* bicarbonate of soda
* old tube of hair conditioner
* old bath bombs
I was going to set up outside and suggest that the children collect additional supplies from the garden – dirt, leaves, and the like – but it started raining so we stayed at the kitchen table.
I made sure we had plenty of kitchen paper and old towels on hand: one of the many learning points was how much liquid does (and doesn’t!) fit into different shaped containers.
oops!
Once I’d shown the children the supplies, I left them to it and busied myself taking photos and notes.
J(8) spent a long time investigating the properties of sand
I didn’t put out food colouring in the interests of economy, but provided it at C(9)’s request – she wanted a more intense colour without water.
C(9) wondered, “How can I make this even more bubbly?” Later, she filtered her potion.
Of course, the leftover cornflour and coloured water had to be made into gak
C(9)’s potions after she’d left them to settle a few hours
The children had so much fun doing this, and I loved watching them learn as they played. Free-style potions has something for everyone!
Spontaneous science – “I wonder if orange is more or less acidic than lemon?”
Science is my favourite homeschool subject. I love it because it’s hands-on, my kids are always enthusiastic about it, and it’s so varied – there’s always a new way to make things pop, whizz, bang or explode!
To get straight into how we do science, skip down to “How I plan (or don’t plan) science” below.
Free range science
Science is: an objective, self-correcting method for gathering and organizing information about the natural world through repeated observation and experimentation.
Robert Krampf (“The Happy Scientist”)
One of the biggest benefits of homeschooling is the abundance of time children have to explore and gather information about the natural world during their everyday lives.
My kids “do science” while they’re playing in the garden – whether they’re designing rope swings, making mud and berry pies or just lying on the trampoline gazing up at the trees. They’re “doing science” when we’re out with our dog in the woods or by the river, admiring wildflowers and distinguishing breeds of geese. And they’re “doing science” when they combine ingredients and follow recipes in the kitchen when they cook lunch or bake cookies for poetry tea.
Kitchen science – home-made butter
I wouldn’t want any formal science curriculum to take my children (aged eight and nine) away from these free-range explorations. The way I see it, there’s plenty of time for learning how to formally write up experiments. My goals right now are for my children to enjoy finding out about the world about them, and for them to think of “science” as something that they enjoy.
As with our other subjects, despite not using a science curriculum I try to find a balance between giving my children time for their own explorations, and sharing with them the delights of the world as I know it. So we “do science” as a subject, in a variety of ways.
Strewing and projects
The least formal ways we do science are via strewing and project time. I strew interesting materials – a prism, a magnet, a book about space, a DVD about whales – and often the children will explore them and ask questions. Sometimes this leads to a project. C(9) spend a couple of months learning about electricity, during which time she and her brother played with snap circuits every day.
Project-based homeschooling – experimenting with circuits
At the moment she’s finding out about light and colour, which involves activities like burning crisp packets with a magnifying glass and making rainbow iced cookies.
Playing with a prism
Field trips
Another perk of homeschooling is the time we have to go on field trips. Whereas school children might visit the London Science Museum or Natural History Museum once or twice in their elementary years, we can go as often as we like. We’ve participated in some excellent educational workshops at RHS Garden Wisley, Benjamin Franklin House, our local zoo, and even a University space laboratory.
Lightening rod demonstration at Benjamin Franklin House
Because we can go on holiday out of peak season, we’ve been lucky enough to visit the Kennedy Space Centre, and this week, in preparation for cruising the Norwegian fjords in June, we’re learning about how glaciers shape the landscape.
We’ve had time to enjoy weekly trips to our local pond, which is giving us a great chance to observe how the plants and animals there change with the seasons.
Testing pond temperature
How I plan (or don’t plan) science
Science is a huge subject, encompassing everything from nature-study to astronomy. Using a curriculum can help make sure you approach science in an organised way, covering topics in a methodical order – but curriculum isn’t for everyone.
I tried it once – the Pandia Press REAL Science curriculum. We spent a fun term learning about the human body, transporting blood cells around our model giant, using string to map our intestines, and making “blood” out of vegetable oil and kidney beans. But then the curriculum moved onto animals and the most hands-on it got was assembling a lap book, and my kids’ groans at the mention of science told me it was time to do our own thing.
Making “blood”
If I were very organised I’d make a list of core science topics and plan a series of experiments and activities covering those areas. But… if I waited until I’d done that, we’d probably never do science. Instead, I throw perfectionism out the window and leap into actually doing experiments and activities, taking one week at a time.
Each weekend I plan one activity or experiment to do during the week. I take inspiration from many places: books, Pinterest, friends, blogs and DVDs (see below for a list of my favourite resources).
When I say I “plan” an activity, I mean I make sure we have the supplies ready so that on whichever day feels right I can just set everything up and get going.
Supplies at the ready
If I’m having an organised week, I might also:
– research some related materials like You Tube or Brain Pop videos
– find relevant books to strew or read aloud
– read up on scientific principles involved so that I can talk about the activity with the children conversationally, answer their questions, and generally draw out their understanding of what we’re doing
These “organised weeks” only happen about half the time, but imperfect science is better than no science at all.
On the weeks when I haven’t managed to do much in advance, we learn together as we go. I like to see shortcomings in my preparation as opportunities for the children’s ideas to surface. After all, if I planned everything to the last detail, where would be the space for their ideas? 😉
The scientific method
Children naturally follow the steps of the scientific method: they ask questions, make guesses, seek information, try things out and talk about their discoveries. I don’t require my children to make formal records of our experiments, although sometimes they do so anyway.
I have one child who is still working to acquire the cognitive and neurological skills for handling mistakes. No matter how many times I assure him that mistakes are part of learning, point out my own, and read stories about the value of mistakes, getting things “wrong” can cause meltdowns. For this reason, we keep scientific hypotheses very informal and conversational!
Red cabbage indicator
Sources of inspiration
Books
Science Experiments: Loads of Explosively Fun Experiments You Can Do – My absolute favourite source of inspiration. Almost all our experiments this year have come from this book. I’m very visual and terrible at following instructions, so I love the large format, colour pictures and short chunks of text.
Wholly Irresponsible Experiments – Clearly laid out and amusingly framed with sections like “The Scientific Excuse” (which explains the science). Not many pictures though.
Copper plating a nail
The Ultimate Book of Kid Concoctions – One for the summer – full of fun activities like paint and play dough recipes. Nothing you can’t find on Pinterest, but handy to have in one volume.
Sometimes rather than picking an experiment at random, I look for a hands-on activity related to a specific topic. When we were looking at the rock cycle, I searched for “rock cycle hand-on learning” and “fun rock cycle experiment” which led to us doing the crayon rock cycle.
In preparation for our Norway trip in a few weeks, I wanted to teach the children about how glaciers shape the landscape, so I searched for hands-on glacier experiments and found this article which contains a couple of wonderful elementary-level experiments with ice and dirt. I love the internet!
Another reason I love science is because science is the subject in which I learn the most alongside my children.
I remember next to nothing about my own primary school science. I have vague memories of the fun being drained from experimental play by being made to fill in worksheets. And I have a very clear memory of being told, “Whatever you do, don’t put your magnet in the iron filings.” Guess what this curious seven year old did?
The most vivid memories I have are of a five day school trip I went on (aged nine) to a residential science centre. During those precious days I learned that the striped patterns in the cliffs that lined the beaches I’d grown up on were layers of shale, limestone and sandstone. I learned how you can tell how polluted a place is by the colour of lichens. I learned that my left eye was dominant, and that different parts of my tongue were sensitive to different tastes.
I didn’t learn these things by reading a book, or listening to a teacher in a classroom (even though I enjoyed both those activities). I learned the science I remember most by walking on beaches, by rubbing my finger against rough lichen-covered walls, and by moving markers in front of my eyes. I learned by being outside, by doing, by having fun.
Looking forward
You won’t be surprised to hear that I don’t have a detailed plan setting out what we’re doing for science for the rest of our homeschool years. What I do have is a couple of kids who often choose science topics for their project work and who happily drop what they’re doing when I suggest doing a science experiment. In my experience, where there’s enthusiasm, there’s learning.
This post is part of the Homeschool Help series. Next week we’ll be talking about our favourite Apps.
For more ideas about how to do homeschool science, visit:
Hwee at The Tiger Chronicles – Science in our home. How we learn science has evolved.
Savannah at Hammock Tracks – Science with my scalliwags. Science without a formal curriculum.
Nicole at One Magnificent Obsession – The epic failure that wasn’t. Science is so much more fun than a curriculum.
Chareen at Every Bed of Roses – Science in the junior years. It’s about exploring the world around you.
Erin at Seven Little Australians – Kindling and fanning scientific minds. Sharing how our family kindles an interest in scientific matters and how we keep that interest alive.
Bernadette at Barefoot Hippie Girl – Scientifically speaking. Shoes off and hands on.
Disclosure: This post contains affiliate links. I paid for and use all the products linked.
We’ve been so busy at our pond watching the swans and coots nest, we didn’t notice that the ducks had been quietly getting on with it until we visited this week to find a clutch of ducklings!
There were six ducklings on Monday. They were very tame so we were able to study them close-up. The children distinguished one that is the only one with pale stripes along the side of its beak. They’ve named it “Link”.
“Link” with pale stripes on his beak
The new arrivals were so cute we visited them again on Wednesday. This time there were only five ducklings of the original clutch. We were pleased to see our “Link” still among them.
One of our favourite ducks – the one we haven’t been able to identify (a cross-breed?) was nestled on the grass by the water’s edge. We watched her quietly for a while, and then she moved to reveal a single, tiny duckling underneath her!
Hiding her little oneThere he is!
One animal we weren’t so happy to see at the pond edge was this black predator! There are houses all around the edge of the pond so I guess it’s not surprising cats come and try their luck with the tame little ducklings.
In other pond news, our swan is still nesting.
The pair of Egyptian geese are back, having disappeared for several weeks.
Yellow irises are beginning to bloom.
We noticed lots of these (lily?) rhizomes in the shallows. The children decided they were alien pods (very scientific, ahem).
A few hundred yards from our pond is a much more secluded set of ponds. Only a few shy birds swim on these, and they teem with life.
Tadpoles
Pond skater
I wonder how many ducklings we’ll see next week?
For previous pond study posts dating back to early March, see here.
Thanks to AngelicScalliwags for inspiring us to begin our pond study.
Air is always pressing around everything, but we can’t see it. This week we did some experiments that helped us see air pressure in action.
Experiment 1 – Rising water
What You Need
shallow dish
tall glass
candle
clay
food colouring
matches/lighter
water
What you do
1. Place the candle on top of the clay in the shallow dish.
2. Pour in some water and add a few drops of food colouring.
3. Light the candle and quickly place the inverted glass over it.
What happens
When the candle burns out, the water level inside the glass rises.
The scientific explanation
When the candle has used up the oxygen in the glass, the flame goes out. The air inside the glass cools and contracts, and water rises up into the glass to fill the gap.
Experiment 2 – Ice Water Can Crusher
What you need
empty drink can
shallow tray or dish
tongs
ice
water
stove or hot plate (and an old saucepan if, like me, you have an induction hob)
What you do
1. Prepare a tray filled with enough ice to cover its base, and water to cover the ice.
2. Put a small amount of water into the empty can and set it on the stove until the water inside boils. (If you have an induction hob, place the can on the base of an old saucepan.)
3. Quickly pick up the can with the tongs and put it upside down into the tray of icy water so that the opening is under water.
What happens
Very soon after it enters the icy water, the can is suddenly and noisily crushed!
The scientific explanation
When the can is placed in the cold water, the air inside it cools and contracts. The greater air pressure from outside presses on the can and crushes it.
My top tip
We had to do this twice as it didn’t work the first time. I had put too much water in the can and didn’t heat it enough before putting it in the icy water. The second time I used less water and made sure steam was coming out before I put it in the water.
Experiment 3 – Only do this if you have a wide-necked glass bottle
We tried this one but our bottle didn’t have a wide enough opening for it to work properly.
Try to insert a (peeled) hard-boiled egg into the neck of a glass bottle. Observe that the egg is too big to go into the bottle.
Don’t try and get an egg into a bottle this size!
Then drop a couple of burning matches into the bottle and try again. If your bottle neck is wide enough, after a few seconds the egg should be sucked into the bottle. This happens because when the air cools the pressure drops and the egg is sucked in to fill the gap.
Our bottle wasnt wide enough to suck in the egg, but the kids noticed that the egg changed shape because of the suction from inside the bottle. We gave it a bit of a push and the egg broke!
It’s trying to get sucked in …
To get the egg back out of the bottle, turn the bottle upside down and blow hard into the bottle. This increases the air pressure and the egg pops out. (Or do what I did when I forgot these instructions, and instead light a match under the inverted bottle, which also works.)
