Physics · Ch 8 — Heat and Thermodynamics
Adiabatic Process
Adiabatic Process
An adiabatic process has zero heat exchange, , so the first law reduces to : the gas expands only at the expense of its own internal energy (cooling), or is heated by external compression work done on it. This arises either from thermal insulation (Figure 8.28), or simply because the process happens too fast for heat to exchange even without insulation -- a bursting tyre, a rapidly compressed/expanded gas, or warm air rising and adiabatically cooling into cloud droplets (Figure 8.29). The equation of state is (equivalently or ), where is the adiabatic exponent; the adiabatic curve is always steeper than an isotherm through the same point, since (Figures 8.30-8.32). The work done works out to positive (gas co …
What this figure shows. Two thermally-insulated cylinder-piston systems side by side, both wrapped in an explicit insulation layer. The left one, labelled adiabatic compression, shows the piston being pushed inward with an arrow, and text noting pressure P and temperature T both increase as a result. The right one, labelled adiabatic expansion, shows the piston moving outward with an arrow, and text noting pressure P and temperature T both decrease as a result -- demonstrating that in an adiabatic process, unlike an isothermal one, compression genuinely heats the gas and expansion genuinely cools it, because no heat can …
What this figure shows. A set of three small illustrative panels. Panel (a) shows a bicycle or vehicle tyre suddenly bursting, with air rapidly rushing outward -- too fast for any heat exchange with the surroundings to occur even without insulation. Panel (b) shows a gas cylinder being compressed or expanded very quickly by a piston, again too fast for heat exchange despite having no thermal insulation. Panel (c) shows warm, moist air near the Earth's surface rising upward into the atmosphere, expanding adiabatically as it rises into lower-pressure air, cooling as it expands, and its water vapour condensing into visibl …
What this figure shows. Two P-V diagrams, similar in layout to the isothermal Figure 8.25, but tracing steeper curves called adiabats instead of isotherms. The left diagram shows adiabatic expansion from (Pi,Vi,Ti) to (Pf,Vf,Tf), and the right shows adiabatic compression between the same two states in the reverse direction. A caption notes that the adiabatic curve is visibly steeper than an isotherm passing through the same starting point, because the adiabatic exponent γ is alw …
What this figure shows. A gas cylinder with perfectly non-conducting (insulated) walls and base, fitted with a frictionless, insulating piston of cross-sectional area A, shown at two different piston positions corresponding to the initial volume Vi and the final volume Vf. This is the geometric setup the textbook uses, together with the adiabatic equation of state PVγ = constant, to carry out the integral W = ∫P dV and arrive at the closed-form adiabatic work ex …
What this figure shows. Two P-V diagrams (adiabatic expansion on the left, adiabatic compression on the right), each showing the adiabatic curve between the initial and final states drawn alongside two isotherm curves -- one isotherm for the initial temperature Ti and another for the final temperature Tf -- so that all three curves (the adiabat and the two isotherms) can be visually compared. The shaded region under the adiabatic curve represents the work done W in the process, and the figure is used to show explicitly that the adiabat is steeper than either isotherm, since work done is evaluated the same way (as the area under the P-V curve) regardle …