A liquid has a definite volume
and a shape that can vary because the particles in a liquid are kept
together very loosely. This allows the particles to move freely around
each other. Liquids have a low viscosity, meaning a low resistance to
flow.
Let's say you have 20 people and you put those 20 people in a room
for an hour. Over the course of an hour, the people would most likely
move around the room. But, you would always have 20 people there in the
room. The number of people doesn't change unless you add or take away
people.
The same goes for a liquid. If you put 20 mL of water in a cup and
left it there for an hour, there would always be 20 mL of water unless
you added or took away water.
The people would be confined to the room, and the particles of the
water would be confined in the cup. If you took the people and put them
in a larger room, they would spread out and adjust according to the room
because they are free to move. If you took the water and put in in a
larger cup, it would adjust according to the space because they are free
to move.
