A heavy rock sinks, but a boat, equally heavy,
doesn't! Neat! So what gives? The
Biggest factor is the contact area between the
boat and the water (the area where the boat
and water touch).
The secret to floating boats is a problem
of spreading the weight over a large area of
water. If you think of a bunch of water
molecules trying to hold up a boat, they're
pushing against the boat to keep it on top of the
water. If the contact area between the water and
the boat is larger (a large area of the boat is
touching the water), more water molecules can push
against the boat, so they can keep it afloat. You
can think of it like lifting furniture. You might
not be able to lift it alone, but if several
people help out, each person lifts a part of it.
Boats tend to have big flat surfaces on the
bottom (the hull of the boat), which helps them
float. Although they're heavy, they spread
their weight across a large surface in the water.
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