When in balance the torque on one side of the fulcrum is equal to the torque on
the other side of the fulcrum, from which we get the following:
W1 × L = W2 × R (10.5)
where W1 is a weight at a distance L from the fulcrum and W2 the counter balancing
weight at a distance R from the fulcrum.
Example 10.3 Two pounds of potatoes are being weighted with a balance, the counter
weight on the balance is 0.5 lb. If the balance arm from the potatoes to the fulcrum is
6 in long, how far from the fulcrum must the counter balance be placed?
2 lb × 0.5 ft = 0.5 lb × d ft
d = 2 × 0.5/0.5 = 2 ft
Spring transducer is a device that measures weight by measuring the deflection
of a spring when a weight is applied, as shown in Fig. 10.5a. The deflection
of the spring is proportional to the weight applied (provided the spring is not
stressed), according to the following equation:
F = Kd (10.6)
where F = force in pounds or newtons
K = spring constant in pounds per inch or newtons per meter
d = spring deflection in inches or meters
Example 10.4 When a container is placed on a spring balance with an elongation
constant of 65 lb/in (11.6 kg/cm) the spring stretches 3.2 in (8.1 cm). What is the
weight of the container?