Ritwik is buying a new school bag. He picks one with thin, string-like straps, saying it will feel…

Why

Ritwik is correct that thin straps weigh a little less — a few grams, perhaps. But the books inside weigh kilograms, and that whole load still presses on his shoulders through the straps. What decides how much it hurts is pressure: the force divided by the area it acts on. A thin strap squeezes the full weight onto a narrow strip of shoulder, so the pressure is high and it digs in. A broad strap spreads the same weight over a much bigger area, so the pressure on each bit of shoulder is lower. It is the same reason a sharp knife cuts easily (tiny area, huge pressure) and why heavy trucks have many wide tyres. Test: carry a heavy bag of groceries by its thin plastic handles, then again with a folded towel under the handles — same weight, very different feeling. Kirti is right: broad straps make the bag more comfortable because they spread the force over a larger area and lower the pressure.