A simple Cavendish apparatus is described that allows measurement of the gravitational constant G and makes observable the gravitational attraction between commonplace objects. The apparatus consists of a torsion balance constructed from readily available materials, including lead bricks and fishing weights (“sinkers”). A computer program is used to determine the gravitational field at the location of the small mass due to a nearby lead brick, which allows students to gain experience with numerical methods. Experimental results obtained are compatible with the accepted value of G.
References
1.
I.
Newton
, “Principia book III The system of the world Proposition 10, Theorem 10
,” 1687; see I. B. Cohen, Isaac Newton: The Principia
(Univ. California Press
, Berkeley
(1999
), p. 815
.2.
H.
Cavendish
, “Experiments to determine the density of the earth
,” Philos. Trans. London
88
, 469
–526
(1798
).3.
B. E.
Clotfelder
, “The Cavendish experiment as Cavendish knew it
,” Am. J. Phys.
55
, 210
–213
(1987
).4.
I.
Falconer
, “Cavendish: the man and the measurement
,” Meas. Sci. Technol.
10
, 470
–485
(1999
).5.
Clive
Speake
and Terry
Quinn
, “The search for Newton's constant
,” Phys. Today
67
(7
), 27
–33
(2014
).6.
Harold V.
Parks
and James E.
Faller
, “Simple pendulum determination of the gravitational constant
,” Phys. Rev. Lett.
105
, 110801-1
–110801-4
(2010
).7.
Terry
Quinn
, Harold
Parks
, Clive
Speake
, and Richard
Davis
, “Improved determination of G using two methods
,” Phys. Rev. Lett.
111
, 101102-1
–101102-5
(2013
).8.
Terry
Quinn
, Clive
Speake
, Harold
Parks
, and Richrd
Davis
, “Erratum: Improved determination of G using two methods
,” Phys. Rev. Lett.
113
, 039901
(2014
).9.
B.
Block
, R. D.
Moore
, and P.
Roos
, “Do-it-yourself Cavendish balance
,” Am. J. Phys.
33
, 963
–965
(1965
).10.
J. Cl.
Dousse
and Ch.
Rhême
, “A student experiment for accurate measurement of the Newtonian gravitational balance
,” Am. J. Phys.
55
, 706
–711
(1987
).11.
Hans
Meissner
, “Demonstration of gravitational attraction with the Cavendish balance
,” Am. J. Phys.
25
, 639
–640
(1957
).12.
E. M.
Purcell
, “Gravitational torsion balance
,” Am. J. Phys.
25
, 393
(1957
).13.
The wire cost ∼$8 and was obtained from Component Supply Company, 1220 New Hope Road, Fort Meade, FL 33841.
14.
The laser cost ∼$7 and was purchased from Parts Express, 725 Pleasant Valley Dr., Springboro, OH 45066 (model DC-LP11112, part number 073-082). The laser is powered by an Enercell voltage source, but any source of 5 V will do.
15.
William H.
Press
, Saul A.
Teukolsky
, William T.
Vetterling
, and Brian P.
Flannery
, Numerical Recipes
, 3rd ed. (Cambridge U.P.
, New York, NY
, 2007
), pp. 773
–839
.16.
Peter J.
Mohr
, Barry N.
Taylor
, and David B.
Newell
, “CODATA recommended values of the fundamental physical constants: 2010
,” Rev. Mod. Phys.
84
, 1527
–1605
(2012
).© 2016 American Association of Physics Teachers.
2016
American Association of Physics Teachers
AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.
