Ballons-Gas

*We want to study the pressure of the air*

Balloons are stretched or pulled tight by the gases inside. Some balloons float in the air while others can’t. Hot-air balloons don’t have to be sealed

How does the air inflate a rubber balloon?

Its pressure pushes the ballon’s “skin” outward

Air is a gas: individual atoms and molecules

Air has pressure: it exerts a force on a surface

Pressure inside a balloon is greater than outside.

Total pressure forces on ballon skin outward

Balloon is held taut(pulled tight) by those outward pressure forces.

Why doesn’t the atmosphere fall or collapse?

A gradient in its pressure supports its weight

Air and density/ density = mass/ volume

Why does a hot-air balloon float in cold air?

Why does a helium balloon float in the air?

States of matter: Solid, liquid, and gas

Molecules in solid, liquid and gas (diagram shown) - atoms are not destroyed, they still have the same chemical property, they change shape/structure, between the states of matter.

Heat energy- as you increase the temperature the bonds are broken, therefore letting molecules free

Air: components of air

Nitrogen makes 78% of air

Oxygen 20.9% of air

Other gases: less than 0.17%

Argon: less than 0.90%

Air and pressure:

Air consists of individual atoms and molecules

Thermal energy keeps them separate and in motion; since each particle is moving individually they are all going at different speeds.

Air particles bounce around in free fall, like tiny balls.

Air particles transfer momentum as they bounce.

Each momentum transfer involves tiny forces.

A surface exposed to air experiences a force.

The force on a surface is proportional to its area.

The force per area is the air’s pressure.

Pressure = force/ surface area

Pressure measured in units of force per area, called the pascal (pa)

Temperature:

K is absolute zero: no thermal energy available (SI unit of absolute temperature: kelvin or k)

Room temp. Is approximately 300 k

1k is same as 1 celsius

Air temperature is proportional to average thermal kinetic energy per part. (on absolute scale)

Air temperature is related to average thermal kinetic energy per particle. (on conventional scale)