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Lecture from Conceptual Physics, 8 th Ed.

The balloons float because they weigh less than the air that they displace. Air displaced: 1000lbs Air in balloon: 800lbs Lift: 200lbs. Lecture from Conceptual Physics, 8 th Ed. Why is the air in the balloon lighter ?. The Atmosphere p234.

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Lecture from Conceptual Physics, 8 th Ed.

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  1. The balloons float because they weigh less than the air that they displace. Air displaced: 1000lbs Air in balloon: 800lbs Lift: 200lbs Lecture from Conceptual Physics, 8th Ed. Why is the air in the balloon lighter?

  2. The Atmosphere p234 The sun’s heat makes air molecules bounce around. Gravity pulls the molecules back. What you end up with is… Molecules are squeezed together at the bottom and are further apart as you go higher.

  3. Atmospheric Pressure p236 The mass of air in the 1cm2 tube is 1 kg… Magdeburg hemispheres (cross-sectional area 1 m2) There are 10,000cm2 in 1m2 ! or 10 N of downward force. So, the pressure on the outside of the spheres holding them together was 100,000 N. That's Pascal standing next to the mayor BUT, pressure acts in all The horses didn’t stand a chance against 101.3 kPa or 101,300 N/m2. directions.

  4. The pressure (kPa) created by 760mmHg equals the kPa of the air outside. Barometers p238 Vacuum pumps make vacuums…fig.13.11 Less pressure here:

  5. Boyle’s Law p240 P1V1 = P2V2 1. (1kPa)(20L) = (P2)(60L) 2. The kPa of 10.3m of water is 101.3kPa so there are 202.6kPa or 2 atm of pressure on the diver. (2atm)(lung size)=(1atm)( ??? )

  6. Buoyancy of Air p242 A 1 cubic meter object displaces 12 Newtons of air. Archimedes’ principle: An object surrounded by air is buoyed up by a force equal to the weight of the fluid (air) displaced. If a m3 of He weighs 1N, then a 1m3 balloon of He will lift 11 N.

  7. Bernoulli’s Principle p243 When the speed of a fluid increases, pressure in the fluid decreases. Faster flow, less pressure. Applications of Bernoulli’s Principle

  8. More Applications

  9. Plasma p248 Still neutral but containing positive ions (formerly atoms) with an equal number of electrons. Ionized gas Street lights Oh goody, now we can talk about aerodynamics. Fluorescent lights Northern lights

  10. Aerodynamics Wing- provides lift. Vertical and horizontal stabilizers- make it go straight. Fuselage- streamlined to make it go fast. Let’s end the lecture and learn how to fold this glider.

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