1/26/11

Post date: Jan 25, 2011 9:34:56 PM

• • No bell ringer.

  • Quiz 3 - States of matter, changes of state, pressure

  • 3.3 Notes

  • 3.3 Demos

    • • Pressure

        • • The air around us exerts pressure on us. A bottle of water with a single hole in the bottom will not leak because the pressure inside the bottle is equal to the pressure outside the bottle. When the bottle is squeezed, there is more pressure inside than out, so water comes out the hole.

• • • Bernoulli's Principle

      • • A ping pong ball floats on a jet of air from a compressor, hair dryer, or straw. The fast-moving air has lower pressure than the still air around it, which sucks the ping pong ball in.

        • Blowing out through a funnel will capture a ping pong ball for the same reason.

• • Pascal's Principle

    • • Two connected bottles are filled with water. The bottom bottle has holes poked in it. When the top bottle is squeezed, water shoots out of each hole at the same time with the same force. The pressure in the top bottle is transferred evenly throughout the bottle, making water come out everywhere at the same time.

Page 94: 1-9 due tomorrow

Fluids through openings

• • when fluids move from a wide to a narrow opening, they have to speed up to get all the fluid through

  • When fluids move from a narrow to a wide opening, they slow down.

  • example: putting your thumb over part of a hose's opening to shoot water faster and farther

  • example: narrow opening at end of a squirt gun to make water shoot faster and farther

  • example: clear tape over most of sink opening to shoot water fast and get user wet (good April Fool's prank!)

Pressure and movement

• • Fluids generally move in ways that will equalize pressure differences

  • Fluids flow from higher pressure to lower pressure (higher pressure side is pushing them harder than the lower pressure side)

  • Objects in a fluid will move with the fluid according to pressure differences

  • example: Fire One! game (push on pumps to move plastic piece using air pressure)

  • example: Compressed air leaking out of a tire into the lower pressure atmosphere

  • example: Hiss when opening a soda due to higher pressure air (and CO2) inside bottle moving into lower pressure atmosphere.

  • example: ALL WEATHER is driven by differences in pressure