In a deep-sea diving excursion, Keiji notices that the strap of his diving watch feels tighter on his wrist as he descends to greater depths. His friend Amar, watching from the submarine with a viewport at the same depth, does not feel any change in the fit of his own watch. Why does Keiji feel increased pressure on his wristwatch strap while Amar does not, even though both watches are at the same depth?
Respond very briefly.
As Keiji descends, the water pressure around him increases because the weight of the water above him is increasing. This water pressure applies a force on all surfaces in contact with it, including the strap of his diving watch, which is compressed against his wrist, making it feel tighter. Meanwhile, Amar is in a submarine that is designed to withstand the external water pressure, maintaining an internal pressure similar to surface conditions. Therefore, Amar does not feel a change in pressure on his wristwatch strap, as the interior of the submarine shields him from the increased water pressure.