1

WHY?

Lets Investigate

What is in the plastic bottle and in the tube?

What happened to the rubber sheet as I pulled the plunger?

What do you think pushed the rubber sheet?

Questions

What really happened

Before heating

While heating

We found out that

While cooling

Objects on Earth are surrounded by air.

The air that surrounds us (atmosphere) exerts force at a certain surface area, hence

AIR EXERTS PRESSURE

Key Ideas

Also commonly known as air pressure

Defined as the pressure exerted by the weight of air above

Force exerted against a surface by continuous collision of gas molecules

Atmospheric Pressure

About 1 kg/cm2

14 pounds per square inch

How strong is air pressure?

If air exerts pressure, then why objects on Earth dont crush or collapse?

How is air pressure measured?

An Italian scientist who invented the first mercurial barometer an instrument used to measure atmospheric pressure

Evangelista Torricelli

When atmospheric pressure is higher, the mercury column is pushed taller.

When atmospheric pressure is lower, the height of the column of mercury drops.

Mercury barometer

76 cm of mercury

Normal atmospheric pressure

1 atmosphere (1 atm)

Aneroid Barometer

A portable device that can measure atmospheric pressure

Contains a metal device that is sensitive to pressure difference

The higher the elevation above the surface, the lower the pressure.

The lower the elevation, the higher the pressure.

Introduce Blaise Pascal and his findings

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Atmospheric pressure variation with altitude

One half of the atmosphere lies below an altitude of 5.5 km

So far, we learned that

Air exerts pressure (atmospheric pressure)

Air pressure can be measured using barometers (mercurial or aneroid).

Air pressure varies inversely with altitude.

Why air pressure matters?

Did you learn?

LETS SEE

Get a sheet of paper

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You noticed that the column of mercury in the laboratory starts to drop. How will you describe the weather for the day?

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In which place does air exert less pressure: in a lowland or at the mountains peak? Explain.

28

Boiling happens when the vapor pressure exerted by the liquid is equal to the pressure of the air above it. If this is the case, where is it easier to boil water: in the lowlands or highlands? Explain.

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Why do astronauts and pilots wear highly pressurized suits during their flight or space exploration?

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Always remember that

Air exerts pressure (atmospheric pressure)

Air pressure can be measured using barometers (mercurial or aneroid).

Air pressure varies inversely with altitude.

Knowledge of air pressure is important in dealing with some daily activities such as weather forecasting, cooking and others.