In a belt-drive system, which two tensions are typically evaluated?

• A. Drive and idle tensions
• B. Static and dynamic tensions
• C. Initial and final tensions
• D. Tight side tension and slack side tension

Answer: (D)

Power in a belt drive comes from the difference in tension between the two sides of the belt. One side is pulled tighter by the driving pulley (the tight side) to transmit the torque, while the opposite side remains looser (the slack side). These two tensions are the ones typically evaluated because they determine how much power can be transmitted and how the belt will behave under load. The transmitted power is roughly the belt speed times the difference between the two tensions: P ≈ (tight side tension − slack side tension) × belt velocity. Centrifugal tension can affect both sides at high speeds, but the standard analysis focuses on the tight and slack tensions. Other pairings like static vs dynamic tensions or initial vs final tensions describe different concepts (load states or installation conditions) and are not the primary tensions used to assess belt-drive performance.