Why do students carrying heavy school bags find it easier to use bags with wider straps instead of thin straps?

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1. Why do students carrying heavy school bags find it easier to use bags with wider straps instead of thin straps?

Wider straps distribute the weight of the school bag over a larger surface area on the student's shoulders. Since pressure is defined as force per unit area ($P = F/A$), increasing the area ($A$) while the force ($F$, the weight of the bag) remains constant reduces the pressure exerted on the shoulders. This lower pressure makes the bag feel more comfortable and easier to carry.