Sage Journals: Discover world-class research

Abstract

We consider a constantly accelerating car as well as a control volume consisting of the car without the wheels. The work done on this system is by an external force from the drive wheel, which has a small mass relative to the car, on the axle. We show that this external force is approximately equal to the external frictional force at the bottom of the tire, where it is not applied through any distance, and so no real work is done. The amount of work done by the external force at the axle of the wheel-less car is approximately equal to the value of the pseudowork for the full car (including wheels). The mass of the drive wheel plays an important role in the full energy equation of the wheel-less system, since rotational and kinetic energies are imparted to the wheel, and the overall change in energy of the wheel-less system is negative.

Keywords

pseudowork real work forces on a car

Get full access to this article

View all access options for this article.

References

Penchina

C. M.

, ‘Pseudowork-energy principle’, Am. J. Phys., 46(3) (1978), 295–296.

Sherwood

B. A.

, ‘Pseudowork and real work’, Am. J. Phys., 51(7) (1983), 597–602.

Arons

A. B.

, ‘Developing the energy concepts in introductory physics’, The Physics Teacher, 27(7) (1989), 506–517.

Kumar

, ‘Pitfalls in elementary physics – 3. Work and energy’, Resonance 3(12) (1998), 69–77.

The notation ‘sys’ was adopted from Bruce Sherwood after we brought this system of a wheel-less car to his attention. He found the system to be interesting and wrote about it (with some changes in the drive train and engine placement) on his blog. Sherwood

B. A.

, ‘Work and energy for an accelerating car’, at http://matterandinteractions.wordpress.com/2012/01/09/work-and-energy-for-an-accelerating-car (retrieved 10 January 2010).

The same thing was noted on a web page by Marianna Breinig, who could not find a book which discussed how friction accelerates a car (per e-mail discussion on 15 October 2012). See http://electron6.phys.utk.edu/101/CH2/wheels.htm or http://electron9.phys.utk.edu/phys135d/modules/m6/situations.htm.

Pseudowork and Real Work for a Car

Abstract

Keywords

Get full access to this article

References