Week 5 - Fluid Technologies

1 Pressure

 
Lesson 17: Pressure

Textbook Readings

ScienceFocus 8
Pages 71, 73-75
or
Science in Action 8
Page
s 53, 56-59

Both gasses and liquids are considered fluids but only gasses are compressible. Which means that gasses can be squished into a smaller space but that liquids and solids can not. Liquids transfer pressure .
Background Information
Air Pressure Like everything on earth, the air in our atmosphere is being pulled down by gravity. Air pressure is strongest close to the Earth.
More molecules = more weight = more pressure
Air pressure decreases as you move further away from the Earth, therefore air pressure changes with altitude. If you go for a ride on an airplane or dive in the mountains, you ears "pop" as your body adjusts to the change in pressure.
As air is heated, the molecules move farther apart and the air in the balloon becomes less dense. The balloon floats up in the air.

As air is heated, the molecules move farther apart and the air in the balloon becomes less dense. The balloon floats up in the air.

As the air in the balloon cools. The molecules move closer together and the balloon becomes more dense. The balloon returns to Earth.


 
Barometer
Air pressure is measured using a barometer. A simple barometer consists of a thin glass tube in mercury. As the air pressure
  • pushes down on the mercury in the dish the pressure forces the mercury to rise up the narrow tube.
  • decreases the mercury level in the glass tube goes down.
  • increases the mercury level in the glass tube goes up.

Water Pressure

 

Water pressure also changes as you move downward. As a diver moves deeper in the water the pressure increases because the molecules are packed closer together. Water is not compressible, as shown above, but it is under increasing pressure as the depth increases. Since the pressure is already evenly distributed, because the molecules are already close together, the temperature of the water doesn't increase as its depth increases. Another reason the temperature doesn't increase is because it is further from the source of heat (the sun). There are locations in the ocean, however, that are hotter the lower you travel but that is because those areas are close to a different heat source. These heat sources are vents from cracks in the Earth's crust where magma is closer to the surface of the crust in those locations.



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