Physics 18 Questions

Thermodynamics is from the Greek root meaning movement of heat. "The study of heat and its transformation into different forms of energy." Coined by Lord Kelvin

Macroscopic, because atoms were unknown at the time thermodynamics was created. "early workers had only vague notions of atoms, and knew nothing of elections and other microscopic particles; their models invoked macroscopic notions: mechanical work, pressure, temperature."

the gas will contract 1/273 of its volume for each degree C decrease, given constant pressure. Suggests that the limit of coldness is -273.15°C-- absolute zero.

the gas pressure will decrease 1/273 of its pressure for each °C decrease, given constant volume. Suggests that the limit of coldness is -273.15°C-- absolute zero.

The gas will contract to a zero volume by this rule. Clearly cannot have a substance with zero volume!

-273°C 0 Kelvin *and -459.7°F!

Thermodynamics concerns *changes* in internal energy from a substance, because measuring the amount can be complex. Indicated by changes in temperature. Internal energy is the total E (KE+PE) of submicroscopic particles that make up a substance.

Two systems in thermal equilibrium with a third system are in equilibrium with each other. So named after 1, 2, 3rd laws named.

Adding heat flow to the law of conservation of energy gives the first law of thermodynamics. *"When heat flows to or from a system, the system gains or loses an amount of energy equal to the amount of heat transferred."* Heat added to a system = increase in internal energy + external work done by the system.

a well-defined group of atoms or objects, molecules, particles. ex.) body of a living creature, steam in a steam engine, Earth's atmosphere

The heat added to a system is equal to the change in internal energy plus the external work done by the system.

mechanical work done on a system: internal energy increases temperature increases

No heat enters or leaves the system. "impassable" thermally insulate the system

work *on* system: internal energy increase. Bike pump use warms up. work *by* system: internal energy decreases. Open tire escaping air cools down valve.

Air temperature rises as heat is added or as pressure is increased. Air temperature may be changed by +/- heat, changing pressure of air (involves work), both. Solar radiation (heat) moisture condensation warm ground contact

Air temperature rises (or falls) as pressure increases (or decreases). Characteristic by parts of air (parcels) pressure lessens, allowed to expand and cool. Reduced pressure = reduced temperature.

Rising air cools. Sinking air warms up. Decreasing and Increasing T

When higher elevations in the atmosphere are warmer than lower elevations. Usually higher elevations are cooler than lower elevations. *mountains vs valley weather!

Adiabatic processes can even occur in the liquid ocean (deep currents circulating per 1000 years) and inside Earth (convection currents in molten material under crust)

Heat of itself never flows from a cold object to a hot object. In winter, heat flows from warm inner house to cold outer air. In summer, heat flows from hot exterior to cooler interior. Heat flow = from *hot* to *cold*

Heat flows into a system from a hot reservoir, work is done by the system, and heat flows out to a cold reservoir

Undesirable discarded heat *expelled heat from oven on a hot summer day= undesirable *expelled heat from laundry on a cold winter day= desirable

The second law expresses the *maximum* efficiency of a heat engine in terms of hot and cold temperatures. When work is done by a heat engine operating between two temperatures, *T*(hot) and *T*(cold), only some of the input heat at *T*(hot) can be converted to work, while the rest is expelled at *T*(cold). "All systems tend to become more and more disordered as time goes by."

To prevent the backward push on the turbine blades by exhaust gasses Without condensation (pressure), counterproductive

High-quality energy is organized. ex.) gasoline, turbulent water Low-quality energy is disorganized. ex.)dispersed thermal energy, water pooled after waterfall

High-quality energy tends to transform into lower-quality energy. Order tends toward disorder. Quality of energy is lowered with each transformation, as energy degrades

Natural systems tend to go from order to disorder unless work is done on them to bring order out of disorder. *Open lid of bottle; molecules escape and disorder; will not order back into bottle!

Entropy: natural dispersing or degrading of energy. ex.) Energy locked in chem bonds in wood degrades when wood burns. Total amount of entropy in a system tends to increase with time (while available energy for work decreases) *batteries go dead even w/o use

1st law has no exceptions. 2nd law exceptions are possible but improbable. Law nutshell: "You can't win" (can't get more output than input) "You can't break even" (can't get as much output as input) "You can't get out of the game" (entropy forever increases)

No system can have its absolute temperature reduced to zero.

The pressure is increased, thus air temperature increases as per the 1st Law and meteorology: Air temperature rises as heat is added or as pressure is increased.

Sunlight is the ultimate source of energy in coal, oil and wood. However, the energy in wood is renewable relatively quickly by new growth, while coal and oil's energy is from the Sun of many years ago.

Ideal efficiency proves an upper limit to all heat engines. Friction is always present in all engines, and efficiency is always less than ideal. Only some of the heat can be converted to work, even if the environment conditions are ideal. Heat is expelled to the environment via the cooling system and exhaust.

The heat flow will be from the warmer kitchen air to the cooler refrigerator.

The refrigerator uses a pump to move a fluid around, compress and evaporate the fluid, causing it to absorb and release heat. The cooling of the interior of a refrigerator does not violate the laws of thermodynamics because work has to be input to the system in order to run the compressor that helps pump the heat out of the refrigerator.In each instance where there is heat transfer, the heat moves from the warmer to the colder part of the system - in keeping with the second law. Also, the 2nd Law can have exceptions.

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