» Atwood's machine (0650)
Immagini
DESCRIPTION
Exhibit 650 is a large Atwood's machine designed to study the motion of a mass in free fall and to measure the acceleration (g) due to gravity.
The apparatus consists of two wood columns 2.5 meters high with a tribometer mounted on the top. The tribometer is a system to reduce the friction and consists of a pulley "R" and two pairs of interconnected wheels r,r,r',r'. See Image-1
The axis of pulley R rests on the circumferences of each pair of wheels to which it transmits its motion, thus reducing the friction. In the groove of the pulley, there is a thin silk thread to the extremes of which are attached two equal masses "M". These masses are in equilibrium in any position. When a small mass "m" is added to one of the masses, (M+m) begins to descend with acceleration "a" less than "g" as indicated in drawing-1.
One can calculate the acceleration "a" in the following way:The force acting on the mass (M+m),
![Equazione: [ (M + m)g -T = (M + m)a \eqno{i}]](/foto/equaz/650_eq01.png "Equazione: [ (M + m)g -T = (M + m)a \eqno{i}]")
where "T" is the tension in the thread; "a" is the acceleration of the system.
The force acting on the mass (M) is:
![Equazione: [ Mg - T = - Ma \eqno{ii} ]](/foto/equaz/650_eq02.png "Equazione: [ Mg - T = - Ma \eqno{ii} ]")
Solving for "a", one obtains;
![Equazione: [ a = \frac{mg}{2M+m} ]](/foto/equaz/650_eq03.png "Equazione: [ a = \frac{mg}{2M+m} ]")
By choosing opportune masses, one can obtain an acceleration much smaller than "g" and thus a precise value for "g". To ease the mass motion study, there is a ruler, graduated in centimeters for measuring distance and a pendulum for measuring time. There is also a mechanical release so that the pendulum can with precision release the motion in a known position of the pendulum.
BIBLIOGRAPHY
- [1] A. Ganot, "Trattato elementare di Fisica Sperimentale ed Applicata e di Meteorologia con una numerosa raccolta di problemi", Milano, Francesco Pagnoni, Tipografo-editore, 1861
- [2] Elroy M. Avery, "School Physics", (New York: Sheldon and Company,1895),page 110.
- [3] URL [ http://www.phys.uniroma1.it/DipWeb/museo/Meccanica/atwood.html ]
- [4] Thomas B. Greenslade,Jr, "Atwood's machine", The Physics Teacher, January 1985. Pag.24.
Dati Catalografici
| Data di costruzione: | --- |
|---|---|
| Data di carico: | anteriore al 1835 |
| Nr. Inventario: | 71 (Generale dal 1874) 37 (Antico inv. Gabinetto Fis) |
| Costruttore: | Costruttore sconosciuto |
| Materiale: | legno, ottone, laccato |
| Dimensioni: | Base: Larghezza 65cm, profondità 65cm altezza 250cm |
| Conservazione: | buono |