Equipment:
Theory: To maintain equilibrium, the torque exerted by the spring scale must balance the gravitational torque. The further away from the hinge the spring scale is placed, the smaller the force necessary to produce this torque. Also, the further out the hanging weight is, the more impact it has.
Description: This is a simple demo, but it really gets across the idea of torque. As the spring scale is moved around the students will see the force change - it's important to point out that the torque is constant; the force must change to keep the torque constant. The hanging weight can be slid along the bar to change the required torque; this again is reflected in a change in the reading on the spring scale. The spring scale can also be held so that it's not perpendicular to the rod; this increases the force required to produce the necessary torque.
To put this together, clamp the steel rod horizontally on to the desk, with about 20 cm of it hanging out in front. Slide the T-connector on to the rod; place the end of the aluminum rod into the base of the T and clamp it. The aluminum rod should now rotate freely, the rotation axis being the steel rod.
Slide a hook on to the aluminum rod - this hook is supported by the spring scale. The force exerted by the spring scale changes as the hook is slid back and forth along the rod. Clamp the hook in place when illustrating what happens when the force is exerted at an angle that is NOT perpendicular to the rod. Placing the hanging weight over the rod and sliding it back and forth will also change the reading on the spring scale. All of this should make it clear to the students that both the force and the distance are important when determining torque.
Setup time: 10 minutes
Other demonstrations in this category : Torque wrench 1J40.15 -- Meter-stick balance 1J40.20 -- Loaded beam 1J40.40 --
Previous category : Resolution of forces - Suspended block 1J30.10
Next category : Dynamic torque - Tipping block 1K10.10