1 / 16

Adding Heat

Explore the concepts of adding heat, raising temperature, latent heats, and phase changes in the context of Lance Armstrong's climb in the 2004 Tour de France on Alpe d'Huez. Calculate work, energy expenditure, temperature changes, and more.

jflannagan
Download Presentation

Adding Heat

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Adding Heat Raises energy

  2. Board Work The 2004 Tour de France Alped’Huez time trial stage was a climb with a finish 1200 m higher than the start. The winner, Lance Armstrong, had a mass (with gear) of 84 kg. • Assuming friction is negligible, how much work did he do on the climb? • Muscle is about 20% efficient. How much energy did he expend? • How much became thermal energy?

  3. Raising Temperature by adding heat § 12.7

  4. c = q mDT Specific Heat (Capacity) • Heat needed to change the temperature of a unit amount of a substance. • q= heat input • m = mass of sample • Dt = temperature change • Units: J/(kg K) or cal/(kg K) or J/(mol K)… • Intensive

  5. Board Work • Show that DT = q/(mc)

  6. Board Work • Lance Armstrong’s mass was 75 kg. Assume c = 4184 J/(kg K). If he were a closed system, what would have been his change in temperature?

  7. Latent Heats of phase changes § 12.8

  8. Solid Water (Ice) Source: M. Chaplin, Water Structure and Behavior. www.lsbu.ac.uk/water/ice1h.html

  9. Solids • Strong connections between atoms • rigidity and elasticity • Atoms vibrate about fixed positions

  10. Phase Changes • Potential energies: Solid < Liquid < Gas • During a phase change, potential energy, not kinetic energy (temperature) changes. • Heating or cooling a changing phase does not change its temperature!

  11. Evaporation of a Liquid • More energetic jostling = higher temperature • An especially fast molecule at the surface may detach.

  12. KE PE Evaporation • Evaporating molecules carry away energy • Remaining liquid cools (KE decreases)

  13. Melting of a Solid • Solid structure maximizes favorable interactions • Higher energy allows more movement • Molecules slow as potential energy increases

  14. steam Water boils Liquid water Ice melts ice Heating Curve for Water

  15. Latent heat • Potential energy of phase change (energy required to change the phase of 1 kg of substance) • Water’s latent heat of fusion (melting): 335,000 J/kg • Water’s latent heat of vaporization: 2,255,000 J/kg

  16. Whiteboard Work • During the Alpe d’Huez climb, how much sweat would Lance have needed to evaporate to keep his body temperature constant? The heat q needed to vaporize a mass m of water is q = m (2.255 106 J/kg). Solve for mass m and substitute in the values.

More Related