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If we drop these two objects in water, the seed will still float, and
the rock will still sink. Why? Because the volumes are different. The
two objects have the same mass, but the mass is more concentrated
in the piece of rock. The rock is
more dense
than the seed.
Density
is the amount of mass compared to the volume. Imagine
that we can scrunch both objects into perfect spheres. The mass will
still be the same, but now we can compare the volumes.
The rock has the same mass as the sunflower seed, but in a smaller
volume, so the rock is more dense. But why does the rock sink and
the seed float? Look at the same mass of water.
Compare the rock and sunflower-seed spheres to an
equal mass of water. The volume of the water is larger
than the volume of the rock, but smaller than the volume
of the sunflower seed. The rock is more dense than the
water, so it sinks. The sunflower seed is less dense than the
water, so it floats.
Water Density
Why does warm water form a layer on top of room-
temperature water? Water particles move faster when water
gets hot. Particles push one another farther apart. The water
expands. When water expands, the mass stays the same,
but the volume increases. What happens to the density?
Look at the glass of layered water. Which is the hot
water? Which is the cold water? How do you know?
Rock
Sunflower seed
0.1 g
0.1 g
Rock
Water Sunflower seed
0.1 g
0.1 g
0.1 g
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