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Notes on Think for Yourself questions
What would happen if two or more water particles with
low energy meet?
They would not have enough energy
to overcome the holding power that particles have for each
other, so they would join together.
What would happen to a clump of water particles if
an air particle collided with it?
If the air particle had enough energy,
it would break up a small group or knock some water particles
out of a bigger group. (Note: a collision with a high energy
water particle could also split up a group, but there are
more air particles than water particles).
How would these collisions affect whether or not we
see droplets of water in the liquid state?
If there are only small numbers of
particles together we wouldn’t see any droplets, but
if there are clumps containing large numbers of particles,
then we should be able to see droplets. If collisions with
high energy particles break up the groups of particles as
quickly as they form, there will not be enough particles together
for us to see droplets.
What will happen if the mixture of water and air around
you is cooled (probably before it even reaches 0°C)?
As the temperature drops, the number
of high energy air particles goes down. There will be a point
when the air particles cannot prevent the water particles
from grouping together. If the air is cooler, there
would be fewer particles with high energy (which could break
up the groups of water particles) and more with medium and
low energy. The water particles would exchange energy with
these particles, so there would be more water particles with
low energy, too. We would not see droplets of oxygen or nitrogen
in the liquid state because the particles have a much weaker
holding ability.
A note about water in the gas state.
The bubbles in boiling water are water in the gas state. Even
at just above 100°C we now know that there will be
some low and medium energy water particles. However, at this
temperature there are enough high energy water
particles to stop the lower energy particles joining together.
As a whole, the sample stays in the gas state.
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Science Enhancement Programme CD-ROM 2005 |
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