dec notes
Dec 1, 2007
Mrs. Bowers
Energy
Heat v. temperature
Odors are caused by moving particles – all matter is made of tiny, moving particles – atoms and molecules – held together by chemical bonds
Faster movement – greater kinetic energy
kinetic theory – all particles in motion; forces of attraction between particles, and without forces, particles would drift apart;
scientists need to know how much energy is in a sample of matter – how many calories?!
Temperature is measure of ave KE in a sample; measured in Kelvins (temp is INTENSIVE)
273 K = 1⁰C
⁰C = 5/9 (⁰F+40) – 40
⁰F = 9/5 (⁰C+40) – 40
Examples:
33⁰C = 91.4⁰F = 306 K
90⁰F = 32.2⁰C = 305.2 K
⁰C: 30 is hot, 20 is nice, 10 is cool, 0 is ice
Heat (thermal energy) is the total energy of all the particles in a sample of matter (not just KE); depends not only on ave motion of particles (ave KE), but on the total number of particles (heat is EXTENSIVE)
Example: pull bucket of water out of a pond. Initially, they both have the same temperature, but they have different amounts of heat because there are more molecules in the pond.
Heat is measured in terms of amount of energy added or removed to the system
If the mass of an object increases, the thermal energy of the object increases
Heat is thermal energy that flows from something with a higher temperature to something with a lower temperature. *You never “let cold in” by opening a door – you are letting heat out!
Heat is measured in Joules.
Different substances have different capacities for absorbing heat. The amount of heat energy to raise the temperature of 1 g of a substance 1⁰C is the specific heat. The specific heat capacity is a measure of the ability of a substance to absorb heat. Every substance has its own specific heat.
Substance c (J/g⁰C) c (J/(kgK)
Al 0.9 900
Cu 0.38 380
Au 0.13 130
Ice 2.06 2060
Fe 0.45 450
Pb 0.13 130
Steam 2.06 2060 ???
H2O 4.184 4184
Alcohol 2.45 2450
Graphite 7.10 7100 ??? s/b 0.710
Sand 6.64 6640 ??? s/b 0.664
Website with list of specific heats for solids:
www.engineeringtoolbox.com/specific-heat-solids-d_154.html
The thermal energy of an object changes when heat flows into it or out of it, and that heat flow CHANGE is related to the mass of the object, the object’s specific heat, and the temperature change.
Q = m * C * ΔT or Q = m * C * (Tf-Ti) DO pay attention to positive & negative temp change!
Change in thermal energy = mass * specific heat * change in temperature
Example: A 32 gram silver spoon heats from 20⁰C to 60⁰C. What is the change in its thermal energy?
Q = 32g * 0.235 J/(g⁰C) * (60⁰C - 20⁰C) = 300.8 J
A 45-kg brass structure gains 180,480-J of thermal energy as its temperature increases from 28⁰C to 40⁰C. What is its specific heat?
180,000 J = 45 kg (C ) (40-2 
⁰C C = 180,480/(45 * 12) = 334.2 J/(kgK)
Dulong-Petit Law – law of specific heat – sp. ht. of a solid element is inversely related to its atomic weight
Change of State
When you want to heat a solid to melt, it takes heat to raise temp to the melting point, then more heat to melt the substance.
Heat of fusion (Hf) – heat required to melt – change a solid at its melting point to a liquid at the same temperature
Heat of vaporization (Hv) – heat required to vaporize – change a liquid at its boiling point to a gas at the same temperature
1) the ice rises in temperature from -10.0 to 0.00 °C.
2) the ice melts at 0.00 °C.
3) the liquid water then rises in temperature from zero to 100.0 °C.
4) the liquid water then boils at 100.0 °C.
5) the steam then rises in temperature from 100.0 to 120.0 °C http://dbhs.wvusd.k12.ca.us/webdocs/Thermochem/Time-Temperature-Graph.html
see also:
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/ttab.html
Heat Transfer
Conduction – transfer of heat/thermal energy through matter by direct contact between particles; transfer by collision; like kicking a soccer ball
Convection – transfer of energy by the motion of the heated particles in a fluid; the more energetic the fluid is, the more the particles move and carry their energy. When heated, the volume increases – the particles expand and have less density – because the density is lower, the hot particles rise to float above cooler particles (which are denser because they are closer together).
Convection currents transfer heat from warmer to cooler parts of the fluid.
Radiation – heat that travels through space in the form of electromagnetic waves. When the wave strikes something, some energy is absorbed, and some energy is reflected. The amount of energy absorbed or reflected depends on the type of material. When radiation is absorbed, thermal energy is increased. Gases absorb less radiative energy and transmit more because gas molecules are far apart and the waves pass through – have fewer collisions. Solids and liquids absorb more and radiate less – particles are closer together so the heat stays within the substance better.
answers - jan 12
January 12, 2008
Kylie Hughes
Jean DeMerritt
Amy Lester
Kristy Jernigan
Answers to Exercises
1. Aluminum conducts heat into the potato.
2. The scissors conduct heat away from your skin and the pencil insulates.
3. Metal will conduct heat away from their hands, and their skin will get very cold very quickly. The mittens are insulators.
4. As the steam condenses, it releases heat energy to the room. The heat is conducted through the metal pipes to the air.
5. As sweat evaporates, the liquid must absorb energy to turn into a gas. It takes the energy from your skin which makes you feel cooler. Fanning allows the process to go faster.
6. It’s the same reason we sweat; they fan the air, water evaporates and absorbs heat, making the hive cooler.
7. It would last longer in a small ice chest because it has less internal energy and less room for the particles to gain energy and melt.
8. The faceplates are gold-plated to help protect astronauts by reflecting radiation from the sun. The white material reflects radiation also, helping the astronauts to control internal temperature.
9. No; because as cool air circulates out the refrigerator, the cooling unit kicks in and releases extra heat out of the back or bottom as it pulls heat out of the refrigerator.
10. There’s a smaller percent of surface area exposed to the air in an apartment, and since heat rises, lower floors are helping heat the upper floors, which conserves energy for everyone.
11. The water from the damp cloth evaporates, absorbing energy from the canteen, helping to keep the liquid cool.
12. Their suits are heavily insulated, so the heat from their bodies stays inside the suit. They use liquid because water has a high specific heat and can absorb a lot of energy without a big change in temperature.
13. Energy can escape.
14. It holds the heat in so energy can’t escape.
15. As you exercise, you use energy at a faster rate. You need more and more oxygen so your cells can process glucose and make the ATP you need for energy. You have to breathe harder and faster to keep up.
16. They heat up in the sun, and the smelly molecules also heat up and travel by convection. Heat rises and circulates.
17. They shiver to warm up their bodies to allow faster circulation, and so they can move faster.
18. It depends on how “slight” the breeze is and on the humidity. (We are runners.) In high humidity (like where Kristy grew up), running with a slight breeze feels hot and stuffy, while running against the breeze helps cool you as sweat evaporates. In low humidity (like here in west Texas), sweat evaporates either way, and running with the breeze uses less energy. Even in high humidity, if the breeze is strong enough, it’s better to run with the wind.
19. A geodesic dome has the least surface area.
20. The thermal pollution would radiate to the ground and destroy the ecology.
21. Oranges would freeze first because they are smaller and have less water. The specific heat of the water would help keep them from freezing, and the grapefruits have less surface area per unit of volume.
22. The wind can travel both under and over the bridge and causes the water to freeze quicker.
23. More than 8 inches won’t have a big effect in insulating ability, and it would also get pretty heavy. Trying to pack more snow would just tire her out without much of a payoff in insulation.
24. Air inside is air conditioned and cold; air outside is hot and humid. When people go outside, their lenses are cold, and the water in the air condenses on them.
25. The air in the cave is so far underground that it is well insulated. Radiation from the sun doesn’t reach that far, and the ground insulates it, so heat isn’t conducted well from above or below.
26. Reptiles take on the temperature of their surroundings, so they bury themselves or stay in the shade to stay cool. They also stay still to use less energy during the day, and are more active at night.
27. Penguins are helped because lower surface area helps keep them warm – they have less area from which to lose heat. Elephants need to be large in order to have enough surface area to stay cool.
28. Smaller ears lose less heat.
29. It keeps energy consumption down.
30. They release heat – lots of surface area.
31. Air acts as an insulator, so your body heat mostly stays in your body. The water absorbs heat from your body at a much faster rate than the air.
32. Most of the insulation in goose down is air. If it gets wet, it will flatten and not insulate any more.
33. The camel’s fur helps keep heat out.
Thermal Activities
1. The water in the bottle expands and overflows.
2. The balloon expands in the heat, and shrinks when it cools.
3. The weight hangs lower when the wire is heated because the wire expands when it’s hot.
4. This didn’t work very well. We tried heating it with flame, which was dangerous and difficult to get the heat to the band. We used a space heater, but the rubber band didn’t expand very much. It might work better with older, already stretchy rubber bands instead of new.
Problems
1. 273K + 30 C = 310K
2. Q = (750 g)(4.184 J/gC)(80C – 50C) = 94140J
3. ΔL = αLΔT = ΔL = (12 x 10 -6 /C )(15 m)(1C - 29.4C) = .005 m
4. ΔV = βVΔT = ΔV = (1240 x 10 -6 /C)(500 mL)(45C – 20C) = 15.5 mL = 500mL + 15. 5 mL = 515. 5 mL
5. ΔV = βVΔT = ΔV = (207 x 10 -6 /C)(1000 cm3)(80C – 20C)= 12.42 cm3 =
1000 cm3 + 12.42 cm3 = 1012.42 cm3
6. Q = mcΔT: m=Q/cΔT = 1.36 x 105 J/(500K – 345K)(.90 j/gK)= 975g of Al
7. Q = mcΔT = (25g)(4.184 J/gC)(Tf-10C) = (40g)(4.184J/gC)(80 - Tf)=[ Tf-10 = 1.6(80 – Tf)
Temperature Final = 53.1 C
8. Q = mHf =( 1150g)(334 J/g) = (2270g)(.45 J/gC)(ΔTC)
ΔT = 376 C
saturday science - taks resources
These websites have TAKS materials
www.dcschools.com go to Special Projects, then Smart Teaching TAKS Materials - ask Jean about details
www.lubbockisd.org go to Employee Information; Departments; Science K-12; Elementary or Secondary; TEKS and TAKS - this site has all questions from released tests separated by grade level, objectives, and organized by SE’s in PDF and Power Point - I wish I knew who to thank for doing all this work!! 
http://www.roomd113.com/TAKS%20TEST.htm this has a huge amount of information - lots of great links - wow!
http://www.telecampus.utsystem.edu/ - go to Get on Track for the TAKS - has lots of resources for all subject areas - some good video clips and web activities for science. Students have to register and log-in, and it keeps track of all they have done each time they use the site.
saturday science
what to say… Little Samara died last weekend, and it colored the whole week. I keep seeing her playing with Ian, racing together through the bouncy tunnel, sliding and jumping, racing back and forth in the gym - up and down the bleachers, dancing, hugging, laughing… She kept saying all the next week, “I saw you at the game” - Wayland Baptist University had all these air-filled, great big toys for kids to play in and on. They had so much fun. Little people aren’t supposed to die.
