MondayFebruary 25, 2013

(Gas Pressure and Force)

Bell RingerMonday, 2-25-13

What causes this balloon to have the

shape it has?

pressure

Announcements

Happy Peace Corps Week!

AnnouncementsI will be available after

school today until 4:45.

Assignment Currently Open

Summative or

Formative?Date

Issued Date Due Date Into GradeSpeed Final Day

QUIZ 19 S4 2/15 2/15 FRIDAY

WS – The Nature of Gases F19 2/20 2/21 FRIDAY

QUIZ 20 S5 2/22 2/22 3/8

PressureSuppose you have a one-gallon bottle with air in it.

How much air do you actually have?

The expression “a gallon of air” means little unless the

conditions at which the volume is measured are

known.

A gallon of air can be compressed to a few

milliliters, or it can also be allowed to expand to fill an

entire room.

PressureTo describe a gas fully, you need to

state four measurable quantities:volume

temperature

number of molecules

pressure

Pressure and ForceIf you blow air into a rubber

balloon, the balloon will increase in size - the volume

increase is caused by the collisions of molecules of air with the inside walls of the

balloon.

The collisions cause an outward push, or force, against the

inside walls.

Pressure (P) is defined as the force per unit area on a surface.

The equation defining pressure is:

pressure = force/area

Pressure and ForceThe unit for force is

the newton (N).

It is the force that will increase the speed of a one

kilogram mass by one meter per

second each second it is applied.

At Earth’s surface, each kilogram of

mass exerts 9.8 N of force, due to

gravity.

Pressure and ForceGas molecules exert pressure

on any surface with which they collide.

The pressure exerted by a gas depends on volume,

temperature, and the number of molecules present.

The atmosphere (the blanket of air surrounding Earth)

exerts pressure.

Atmospheric pressure at sea level is about equal to the

weight of a 1.03 kg mass per square centimeter of surface,

or 10.1 N/cm2.

Pressure and ForceThe pressure of the atmosphere can be

thought of as caused by the weight of the gases

that compose the atmosphere.

The atmosphere contains about 78% nitrogen, 21%

oxygen, and 1% other gases, including argon

and carbon dioxide.

Atmospheric pressure is the sum of the individual pressures of the various gases in the atmosphere.

Worksheet

Gas Pressure

and Force