Educationsense

The Theory: The Archimedes' Principle states that an object immersed in a liquid is buoyed upwards by a force equal to the weight of the liquid displaced by that object. Thus, he concluded that a floating object displaces an amount of liquid equal to its own weight.

Kitchen Science Experiments: Take two identical pieces of
modelling clay. Make one into a ball, and the other into a flattened boat
shape, then place each of them onto the surface of a sink full of water. What
happens?

Next, put one of your hands flat on the surface of the water, and make a fist
with the other. Which hand is more difficult to push into the water?

Now, blow up a balloon and put it into the water. Does it sink or float? Can
you push it underwater? Is it easy to push it downwards, or difficult? Watch
what happens to the water level as you push down on the balloon. What's happening?
Finally, sort some objects into groups, depending on whether you think they
will float or sink. Were you right? How can you use what you have learned
to produce a set of rules to help you work out whether or not other things
will float? Are there some materials that always float or always sink? Be
careful, as there are often exceptions to rules! See if you can work out definitions
for 'float' and 'sink' without looking them up. Also, as you notice similarities
between things that float, you will become more expert in predicting what
will happen when you try new items in the water.

Vocabulary: Find out what the words 'float', 'relative',
'displace', 'volume' and 'immerse' mean by checking an encyclopaedia or dictionary
(how do these definitions compare with your own?). Can they only be associated
with water, or can they be used in other contexts? (There is an good opportunity
to go off at a tangent here. Also, if you have very young children, consider
talking about the more advanced concepts in simple terms, and leaving the
names for later - perhaps using the opposing concepts of 'float and sink',
'same and different', 'over and under', 'in and out', etc. instead.)
Storytelling: Encourage your child to help you make up a
story, perhaps about an acorn that falls from a tree and is carried away on
the water, or a group of children who sail away on an adventure. How about
a magic island that floats on the water? Or children diving for treasure in
a sunken galleon? If you or your child find it difficult to make up stories,
try depicting the events with paint, pencil or collage and talk about the
story as it unfolds while you work at your crafts.

At The Riverbank: Look for things that float on the water.
Do sticks float? Leaves? Can you see something floating in the water to signal
danger? Are there flotation devices nearby to throw to a person who has fallen
in the water? (This can lead to a discussion about safety at the waters' edge.)
Is there litter in the water? How will this affect the local wildlife? (Again,
this can enable you to digress to a discussion about environmental/ecological
concerns.)

Why do ducks float? A duck floats because its body is light compared
to water. Air is lighter than water, and ducks have plenty of places filled
with air. All their bones are hollow, and feathers trap air against the duck's
body too. In fact, a duck's body has sacs filled with air like mini balloons
to help keep it afloat!

At The Swimming Pool: If you lie flat on the water, you'll notice
that, just like the boat-shaped piece of clay, you can float without trying.
What happens if you wrap your arms around your legs and make yourself into
a ball, like the other piece of clay?!

Remember when you were pushing your hands into the water at home in your kitchen
sink? Well, the water was pushing you back! Whether you sink or float depends
on how much water you have pushing against you. When you make yourself flat,
you are larger, so more water is touching your body and pushing you back.
When you curl up into a ball, however, you are smaller and there is less water
touching you, so it cannot support your weight.

In The Bath: Mark a 'fill level' line on the bath with a
non-permanent pen or a pencil, and fill the bath until the
water touches the line. Now, get in, lie down and check the line you marked
against the water level. Has the water level gone up or down since you got
into the bath? Your body has displaced the bath water. That is, there's not
enough room in the bath for the two of you! Long ago, there lived a great
mathematician called Archimedes. Now, Archimedes was thinking about why some
things float on water while others don't, when he decided to take a bath.
The bath was filled to the brim, so when Archimedes stepped into the bath,
he displaced some water, which ran over the sides of the bath. When he spotted
the mess on the floor, he realised that it was all related to the problem
he had been thinking about. He shouted, "Eureka!" This means "I've found it!"
(Another opportunity to go off at a tangent - great mathematicians, life in
Classical Greece, ancient history, mythology, etc.)

The amount of space an object occupies is called its volume. Just
as the water level in the bath rose when you got in, and the water level in
the kitchen sink rose when you pushed down on the balloon, any object must
make room for its own volume by pushing aside or displacing an equal
volume of liquid. Now, because the water is pushing back at the object, the
weight of the object also has to be considered. As you may have noticed
when you filled the bottles in the sink, the object floats when it has displaced
just enough water to equal its own weight when on dry land. You've probably
noticed that your drink will rise in the glass when you add ice, but why do
you think ice floats?

Research/History: A famous ship called Titanic sank
when it hit an iceberg. Find out where and how it was built, where it was
going, and who was travelling onboard. (There is a huge number of things to
do around this, for example: a typical day onboard Titanic, dressing
up as some of the first class travellers, dramatisations, painting, museum
visits to see items from the same era, etc. You could also watch one of the
film versions and then compare the film production with the historical facts
as we know them, or discuss what you both think of the director's choice of
camera angles, the acting, editing, etc.)