How tightly can I pack wiggling students into a classroom?

Transcription

1 How tightly can I pack wiggling students into a classroom?

2 A bronze sculpture of a cougar is sitting in the sun. In the morning, when the temperature is 20 degrees C, the tips of the ears are 11 cm apart. How much further apart are they when the sculpture heats up to 30 degrees C? α Bronze = A m B m C m D m E. None of the above

3 Thermal expansion: Lengths all change by the same factor (percentage) per degree. L L o T Why linear in temperature change?

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5 A concrete slab is measured with a steel measuring tape in a room where the temperature is at 20 o C and found to measure exactly 10 feet wide. The slab is measured again on a day when the temperature is 27 o C. The measurement will be a) Greater than 10 feet b) Less than 10 feet c) Exactly 10 feet α steel =11 x 10-6 / o C α concrete =12 x 10-6 / o C

6 A concrete slab is measured with a steel measuring tape in a room where the temperature is at 20 o C and found to measure exactly 10 feet wide. The slab is measured again on a day when the temperature is 27 o C. How much larger will the measurement be? A feet B feet C feet D feet E. None of the above α steel =11 x 10-6 / o C α concrete =12 x 10-6 / o C

7 The wrong way that gives the right answer...

8 The right way that also gives the right answer

9 The right way that also gives the right answer Why did wrong way give right answer? Loss of significant digits...

10 You heat a disc with a hole in it. Will the hole expand or shrink, or stay the same? A. Expand B. Shrink C. Stay the same

11 Area Change... What will it be proportional to?

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13 A 2 A o T V V o T 3 V o T

14 2 NEPHI 2:26 And the Messiah cometh in the fulness of time, that he may redeem the children of men from the fall. And because that they are redeemed from the fall they have become free forever, knowing good from evil; to act for themselves and not to be acted upon, save it be by the punishment of the law at the great and last day, according to the commandments which God hath given.

15 Ideal gases: Molecules collide like billiard balls Molecules don t occupy space Never condense into liquids or solids Don t exist Model a lot of things really well!

16 In an ideal gas, if you double the volume of the container, while keeping the temperature and the number of molecules the same, the pressure in the gas A. Decreases B. Stays the same C. Increases

17 Two versions of the ideal gas law

18 r r How big is a mole? If the earth was made out of baseballs. Earth Baseball N V 0.74 V 6 Earth Baseball m m 0.74 r r Earth Baseball Pennies to the moon d d penny moon d 10 moon N m d penny m moles 13 moles

19 In a liter of water moles If I turned that liter of water into steam at 100 degrees C at a pressure of one atmosphere, it would occupy a volume of 1685 liters!

20 Suppose we have two jars of gas, one of helium and one of oxygen. If both jars have the same volume, and the two gases are at the same pressure and temperature, which jar contains the greatest number of molecules? A. Jar of helium B. Jar of oxygen C. Both jars contain the same number. Consider both gases to obey the ideal gas law. Also note that the mass of an oxygen atom is greater than the mass of a helium atom.

21 A half-liter spray can is empty (you can t get more out), at 20 C, room temperature. What is the initial P (in absolute pressure)? How many molecules are still in the can?

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23 A half-liter spray can is empty (you can t get more out), at 20 C, room temperature. You throw it into the fire at 600 C. What is the final P in the can (if it doesn t burst)

24 A half-liter spray can is empty (you can t get more out), at 20 C, room temperature. You throw it into the fire at 600 C. Suppose instead you have.6 moles of water in the can, which becomes an ideal gas at 600 C. What is the final pressure (in atm) assuming the can does not break.

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26 What is the mass of air in this room, assuming it is all O 2. Take V= 1800 m 3 and T= 20 C. M oxygen =32 g/mole