Square dance sound circuit

(1) The force f of the lifting rod is the power, and the gravity of the object is the resistance. According to the balance condition of the lever: f-motion× l-motion =F-resistance× l-resistance, it can be obtained that f-motion =L-resistance× l-motion f-resistance =15× 200n = 40n;

(2) The electrical energy consumed during normal operation can obtain acoustic energy;

(3) The volume knob used in portable audio is essentially a sliding rheostat (or potentiometer). Sliding rheostat changes the resistance by changing the length of the resistance wire connected to the circuit, thus changing the current in the circuit and achieving the purpose of controlling the volume.

So the answer is: 40; Sound; A rheostat (or potentiometer).