Wednesday, November 7, 2001

• Web Project
• Most groups now have links to their web project.
• Borrowed material must be clearly identified and cited, permission is best.
• Chapters 10, 11, 12 are shorter and mostly review from Chemistry, so we will not spend as much time on these chapters.

Chapter 9:  Solids and Fluids

Air drag - additional note to what is in your textbook:
    At relatively low speeds (less than about 10 m/s):  Fair = bv
    At relatively high speed (more than about 10 m/s):  Fair = 0.5DpAv²

Ponderables:

• A person in a boat floating in a small pond throws an anchor overboard.  Does the level of the pond rise, fall, or remain the same? [fall]
• What happens to the water level in a glass as the ice in it melts? [stays the same]
• What happens to the water level in a glass as the ice (with small pebbles) in it melts? [falls]
• Should a golf ball have backspin or topspin for maximum flight distance? [backspin]
• To make a baseball curve to the left, which way should the pitcher spin the ball? [spin to the left]
• Chicago has been called "the windy city."  How does the Bernoulli effect contribute to this nickname? [air speeds increases as it passes through the narrow spaces between the buildings]

When your instructor lays on a bed of nails, how much force does each nail contribute to support his weight? [~150 lbs/1500 nails =  0.1 lb/nail]
• If an angioplasty procedure expands an artery too much so that the diameter is significantly larger than the surrounding region, would the blood pressure be larger or smaller at that point?  How is this similar to an aneurism?

Temperature scales:
    T(Kelvin) = T(Celsius) + 273.15
    T(Fahrenheit) = (9/5)T(Celsius) + 32

Ideal gas law:  PV = nRT
    Note:  Remember that T must be in Kelvin!

Most substances expand when heated, and the rate of expansion depends on the temperate difference and the linear, area, or volume expansion coefficient.

The pressure of a gas is proportional to the average kinetic energy of the gas molecules, which is directly proportional to the absolute (Kelvin) temperature of the gas.  From this relationship, the average (rms) speed of the gas molecules can be calculated, and this is useful for determining whether a planet has an atmosphere based on the escape speed of each type of gas molecule.

Ponderables:

• Why does water at 75 degrees Farenheit feel cold but air at this same temperature feels warm?
• If you get a hot cup of coffee but don't want to drink it right away, should you add cold dairy creamer right away or just before you drink it for the hottest cup of coffee?  Which method of heat transfer is most significant for this problem?
• How should gloves be constructed to minimize heat loss from your hands on a cold winter day?
• Why is it difficult to get a sunburn from sunlight passing through a window?

• (P.2) In terms of energy, how many candy bars does it take to get to the top of Mt. Mitchell?
• P.7 on page 363:  What is the temperature change in the water from the top to the bottom of Niagara Falls (h = 50 m)?
• What is the final temperature when 100 mL of water at 10^oC is mixed with 100 mL of water at 50^oC?
• What is the final temperature when 100 g of ice at -5^oC is mixed with 100 mL of water at 50^oC?
• P.42:  How long does it take for a cup of water to boil when placed in a solar cooker?

P.61:  How much fluid does a runner loose through perspiration?
• Estimate the power of a microwave oven if a cup of water at room temperature boils in 2 min. on high.
• You look "radiant"!  How much?

• Compared with atmospheric pressure, what is the pressure inside an inflated rubber balloon?
• When a balloon is placed in liquid nitrogen, what happens to the pressure and weight?
• Is the buoyant force on a balloon inflated with air more or less than the weight of the air inside the balloon?
• When a deflated balloon is placed on an electronic scale, the scale reads 0.5 g.  When the balloon is inflated, the scale reads 0.7 g.  When the balloon is placed in LN2, its volume is almost zero, and the scale reads 1.4 g.  From these values, determine the magnitude of all the forces acting on an inflated balloon.
• From this example, what can you learn about measuring devices?

• Web Project links - due today
• HW11b - due Monday
• RWP11 - due next Wednesday