Collection
Search Tips
Peer reviewed
ERIC Number: EJ1142653
Record Type: Journal
Publication Date: 2017-Mar
Pages: 4
Abstractor: As Provided
ISBN: N/A
ISSN: ISSN-0031-921X
EISSN: N/A
Entropic Damping of the Motion of a Piston
Mungan, Carl E.
Physics Teacher, v55 n3 p180-183 Mar 2017
The concept of an "entropic force" can be introduced by considering a familiar setup, namely a horizontal cylinder enclosing an ideal monatomic gas by a piston of cross-sectional area "A" and mass "m" that can slide without friction. The surrounding atmospheric pressure P[subscript atm] keeps the piston from flying out of the cylinder. The cylinder and piston have negligible heat capacity (compared to the gas), but the gas is not thermally insulated from the surroundings at room temperature T[subscript R]. Ignore any viscosity or turbulence of the enclosed gas or surrounding air. Two specific and illustrative situations are analyzed here. In the first, the piston is massless, "m" = 0. The piston is temporarily held in place by a pin while the gas is quickly adjusted to initial pressure P[subscript i] = P[subscript atm] and temperature slightly larger than that of the room, say T[subscript i] = 1.1T[subscript R], using a heater and regulator. The piston is then released from rest, v[subscript i] = 0. In the second case, the piston has inertia, "m" > 0, and the gas is initially in both mechanical and thermal equilibrium with the surroundings so that P[subscript i] = P[subscript atm] and T[subscript i] = T[subscript R]. The piston is now given a quick inward push, v[subscript i] < 0. In both situations, the aim is the same: Describe the subsequent evolution of the system.
American Association of Physics Teachers. One Physics Ellipse, College Park, MD 20740. Tel: 301-209-3300; Fax: 301-209-0845; e-mail: pubs@aapt.org; Web site: http://aapt.scitation.org/journal/pte
Publication Type: Journal Articles; Reports - Descriptive
Education Level: N/A
Audience: N/A
Language: English