Pressure Force applied per unit area. Force Area.

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Presentation transcript:

Pressure Force applied per unit area. Force Area

Pressure = Force Area If a ballerina has a force pushing on the floor of 500 Newtons and she is standing on both feet that have an area in contact with m 2 of the floor, what is the pressure she is exerting on the floor?

Pressure = Force Area What is the pressure on the floor if the ballerina then goes on her toes with an area of m 2 ?

So, as area went down, what happened to the pressure?

Types of Pressure Atmospheric pressure - caused by the weight of the air molecules surrounding us - measured by a barometer

Atmospheric pressure Earth's atmosphere is pressing against each square inch of you with a force of 1 kilogram per square centimeter or 14.7 pounds per square inch. The force on 1,000 square centimeters (a little larger than a square foot) is about a ton! Why doesn't all that pressure squash you?

Types of Pressure Pressure of contained gas - caused by particles hitting sides of container - example: air pressure in a tire

Pressure The more often the particles hit the sides of the container, the higher the pressure.

Inflated balloon P inside = P atm

Blowing up a balloon P inside > P atm

What would happen to the balloon if: P atm > P inside

The SI unit of pressure is the Pascal (Pa). 1 Pa = 1 N/m 2 Most common units used for pressure are: Kilopascal (kPa) Atmospheres (atm) Torres (torr) Millimeters Hg (mmHg) Pounds per Square Inch (psi) Units of Pressure

Conversion factors: 1 atm = 760 torr = 760 mm Hg = kPa = 14.7 psi Note: 1 atm is the average air pressure at sea level when the temperature is 0  C. Units of Pressure

How could you increase the pressure of the gas in this container? Factors affecting Pressure

There are three main factors that affect the pressure of a gas:  amount of gas (mass or moles),  volume of a gas, and  temperature of a gas

Amount of a Gas Low pressure Medium pressure High pressure

What happened to balloon in the pressure container? Temperature and volume were held constant As you pumped air out, the pressure decreased and the balloon grew. As you let air back in, the air pressure in the container went up and the balloon shrunk.

As the amount of gas in a container increases, pressure increases. (directionally proportional)

Volume Low volume, high pressure High volume, low pressure

What happened to the marshmallow in the syringe? Temperature and number of particles were held constant As volume increased, the air pressure in the syringe went down and the marshmallow grew. As volume decreased, the air pressure in the syringe went up and the marshmallow shrunk.

As the volume of a container increases, the pressure decreases. (inversely proportional) aslaw/boyles_law_new.html

Temperature Low Temperature, low pressure (moving slower) High temperature, high pressure (moving faster)

What happened to the balloon in the ice? Number of particles was held constant. As temperature decreased, the air pressure in the balloon went down and so it shrunk. As temperature increased again, the air pressure in the balloon went back up and the balloon grew larger.

As the temperature (K) of a gas increases, the pressure increases. (directly proportional)