Take two bottles roughly the
same shape of a milk bottle.
2. Fill bottle
1 right up to the top with cold water.
3. Fill bottle
2 right up to the top with warm water
and add some drops of food colouring.
4. Place the
card square over the top of bottle
2, and keeping it in place with one
hand, turn bottle 2 upside down, putting
it exactly on top of bottle 1.
5. Now carefully
remove the card, then keeping the
bottle necks tightly together, turn
both bottles the other way up –
you have created a volcano is because
the cold water is heavier so it
sinks, pushing the warm water up.
Try the same experiment
again, but this time fill bottle
1 with salty water and bottle 2
with cold water plus food colouring.
you have proved that salt water
is heavier than plain water.