Torricelli’s BAROMETER used a glass tube filled with Hg suspended in a bowl of Hg. The pressure of the air molecules pushing on the bowl pushed the Hg up into the glass tube.

The weight of the mercury in the tube was equal to the weight of the air pressing down on the mercury in the dish.

As atmospheric pressure increases…

The mercury in the tube rises.

Ways to measure Standard

Pressure(0˚C)• 1 Standard Atmosphere is equal to:

• 760 mm Hg• 1013 millibars• 101.3 kPa (kiloPascals)

1kPa=1000N/m2

• 14.7 pounds/in2

• 760 Torr• Dimensional analysis will be used

to convert from one system to another

Buoyancy and Swimming

• Buoyancy is why most people float. Your body displaces water. When the mass of the water you displace is more than your mass, you float.

• Because of buoyancy you weigh very little in water.

Buoyancy• Buoyant Force –

Force that acts against gravity causing objects to seem lighter.

• Fluid trying to enter the space of an object pushes up on object.

• Based on the difference between density of the fluid and the object

Buoyancy

• Ballast tanks can be filled with water or air to change the density of the boat.

Submarine action• Positive buoyancy – density

less than water – floats on top or is rising

• Neutral buoyancy – density is equal to water – remains at constant depth

• Negative buoyancy - sinks