Forces on a Cello String

Oscillations and Waves > Instruments > Strings

DCS# ~1J30.26

FORCES ON A CELLO STRING

APPARATUS

bar with cello string, pulley and clamp	202-06-D
30 lb weight	202-04-E
weight hanger and weights	202-04-E
large right angle clamps	202-01-E2
cello bow	202-06-D

DESCRIPTION

String is 80 cm long, mass is 12.7 g, force needed to make a 70 cm length of it vibrate at D₂ (73.4 Hz) is 30 lb. We show that the force exerted on the bridge of the cello is less than 30 lb by hanging masses on the middle and measuring the deflection.

W = 2T sin θ/4

Thus the total force exerted by strings on bridge (and consequently by bridge on cello) is less than 120 lbs. For maximum impact should be followed by second demonstration in which 120 lb person stands on cello, causing its collapse.

We also show that the note obtained under the above tension is indeed D₂.

-REW