# Gas Pressure_1_ by malj

VIEWS: 10 PAGES: 12

• pg 1
```									Gas Pressure

D. Crowley, 2007
Monday, September 17, 2012

Gas Pressure
To understand what causes gas pressure
Diffusion
 Look at the diagram which shows bromine gas and air contacting
each other.
 The models show the direction the particles take - which one is
correct?
Air                             The cover was removed,
and after about an hour the
glass jar looked like this

Cover

Bromine

Model 1                  Model 2                     Model 3
Diffusion
 Diffusion is the net movement of particles from an area of high
concentration, to an area of low concentration
 So the particles gradually move from where there are lots of
them, to areas where there are less (net just means the overall)
 It’s a bit like lots of football fans leaving a stadium after a game.
At the stadium they are in a high concentration, but as they
leave, they ‘diffuse’ into the streets and travel home, to where
there are less football fans (low concentration)

Diffusion - net movement from a high
concentration to a low concentration
Tyres
 When you ride your bike its important to have your tyres
pumped up - but why do you do this?
 Has anyone ever ridden over bumpy ground with flat tyres?
What was it like?
 Pumping up your bike tyres cushions you against bumps when
you ride, and this is all because of gas pressure…
Balloon
 Draw an outline of a balloon - can you draw the particles, and explain
what is going on?
 Why does the balloon keep its shape when you blow it up? Why does it
loose its shape after a few days? Why can it pop if you blow it up too
much?
Balloon
 Draw an outline of a balloon - can you draw the particles, and explain what is
going on?
 Why does the balloon keep its shape when you blow it up? Why does it loose its
shape after a few days? Why can it pop if you blow it up too much?

Air is a gas. When you blow a balloon
up, many gas particles get trapped
inside.

The particles move around quickly and
randomly, but they often collide with
other gas particles, as well as the side
of the balloon.

When these gas particles hit the side
of the balloon they cause pressure.
The more these particles hit the side,
the greater the pressure becomes.

This is why when you pump up a tyre
too much, or blow a balloon up too
much, it can burst - you’ve caused too
many particles to crash into the side of
the tyre / balloon, causing the pressure
to get too high!

Eventually the balloon will shrink - this
is because they are not completely air
tight. As air escape, the pressure
decreases as less particles are
colliding with the sides (and it shrinks)
Gas pressure
 Gas pressure causes a balloon / tyre to keep its shape

 The pressure is caused by the trapped gas particles colliding into the
sides of the container they are in

 The more particles there are in there, the greater the pressure becomes
(until you try to put too many particles in, when often the balloon pops)!

Gas particles hit the wall of their
container, causing pressure
Heat

   Two balloons, of equal size, will experience different temperatures - one will be
placed in some warm water, the other in cold water…

 What do you think will happen to the particles inside the balloon if it is heated?
(hint: think about what the gas particles do when they get hot)
 What do you think will happen to the particles inside if the balloon is cooled?

   If a gas is heated up, its particles move around more quickly. They will hit the
sides of the balloon harder, and more often. This will then increase the pressure
(and the balloon expands)

   The opposite happens when you cool it - the particles move slower, crash into
the sides with less force, and less often, decreasing the pressure (so the balloon
shrinks)
Custard bomb…
   So why do balloons and tyres pop if you put too much air in? Why do aerosol
cans explode when they get hot?

   Blow up a balloon too much and you’ll have so many particles hitting the side of
it that the pressure will be too great - causing the balloon to pop.

   If a gas is heated up, its particles move around more quickly. They will hit the
sides of the container harder, and more often. This will then increase the pressure
- heat it up too much, and you’ll create too much pressure inside, causing the
container to explode.
Gas Pressure
 Complete gas pressure 1 - stick this into you book…
Gas Pressure
    Get your neighbours book, and mark
the answer in - 1 mark per correct

1)   The particles in a gas are moving
around all the time. The particles bump
into the sides of their container. The
force of the particles hitting the sides
causes pressure. If you put more
particles into a container, there will be
more particles to collide with the
walls, and the pressure will increase

2a) The air pressure inside will decrease
(less particles colliding into the
container)

2b) The bottle will collapse inwards
because the pressure on the outside
(pushing the bottle in) is now much
greater than the pressure on the inside
(pushing the bottle out).

```
To top