ERIC Number: EJ892005
Record Type: Journal
Publication Date: 2007-May
Abstractor: As Provided
Reference Count: 0
Thermodynamics of a Block Sliding across a Frictional Surface
Mungan, Carl E.
Physics Teacher, v45 n5 p288-291 May 2007
The following idealized problem is intended to illustrate some basic thermodynamic concepts involved in kinetic friction. A block of mass m is sliding on top of a frictional, flat-topped table of mass M. The table is magnetically levitated, so that it can move without thermal contact and friction across a horizontal floor. The table is initially stationary, while the block has initial speed v[subscript i] and slides to rest relative to the table. The block and table are inside a large vacuum tank, so there is no air resistance, buoyancy, nor thermal losses to the atmosphere. Furthermore the inner surface of the vacuum tank is a perfect mirror so that the tank does not radiatively exchange heat with the block and table. The block and table are homogeneous, both initially have temperature T[subscript i], and they each have large thermal conductivities so that they rapidly attain a common final temperature T[subscript f] after the block has come to rest. The specific heat capacity of the block is c[subscript b] and that of the table is c[subscript t], and these heat capacities are assumed to be temperature independent over the range of temperatures that arises in this problem. (a) Find the common final speed v[subscript f] and temperature T[subscript f] of the block and table. (b) Find the changes in the bulk kinetic energies K (in the center-of-mass frame of the isolated block-table system), the internal energies U, and the entropies S of the block and table. (c) Discuss the first and second laws of thermodynamics in connection with these results.
Descriptors: Thermodynamics, Physics, Science Instruction, Scientific Principles, Kinetics, Learning Activities, Magnets, Heat
American Association of Physics Teachers. One Physics Ellipse, College Park, MD 20740. Tel: 301-209-3300; Fax: 301-209-0845; e-mail: email@example.com; Web site: http://scitation.aip.org/tpt
Publication Type: Journal Articles; Reports - Descriptive
Education Level: N/A
Authoring Institution: N/A