Hi,
Need some help here...
1. When the main pads of a bicycle pump with the end blocked up.
When a bicycle tire is pumped up, the volume of the air trapped in
the pump is reduced and its pressure is increased.
(a) Explain, in term of the motion of molecules, why the pressure
increases.
(b) In practice, the temperature of the air increases as it is
compressed. Explain why this is so.
2. A thin-walled plastic bottle is sealed and contains dry air
at atmospheric pressure
(a) Explain how the molecules of air inside the bottle exert a
pressure on the wails.
(b) Ice is placed inside the bottle, and the bottle is then
sealed again. The temperature of the air inside the bottle falls
and the bottle becomes partially crushed. Explain, in terms of the
molecules of air inside and outside the bottle, why this
happens.
I agree with SBS n
SMRT that the answer can be found in the textbook. But I
shall help you out with question 2b, which I don't recall the text
including the explanation.
When ice is placed in the bottle, temperature inside the
bottle drops. As a result the air molecules in the bottle lose
kinetic energy, moving slower and colliding against the walls
of the bottle less frequently and violently. This causes
pressure to decrease. Soon after, pressure in bottle becomes so low
that the atmospheric pressure (the external environment) becomes
larger than that in the bottle. With a resultant pressure acting on
the bottle, the bottle becomes crushed.
FYI, examples like why an egg can drop into a bottle after you
heat the bottle and leave the egg on top of the opening also is due
to the above phenomenon. By the way, Physics is a very systematic
subject. At first it appears tougher than Chemistry but when you
really really find time to do more and explore more questions,
you'd realise the explanations are very alike. So, practise
more!
Thanks.