Density is a basic physical property of all matter. Every
substance has a density that can be measured and the density
of a substance is always the same. If you were asked, which
do you think is heavier, a kilogram of feathers or a
kilogram of lead, your initial response would probably be
the lead. Surprisingly, they both weigh the same amount. How
is this possible? A kilogram of feathers takes up a large
amount of space, or volume. A kilogram of lead is small
enough to hold in your hand. The kilogram of lead takes up
less space because lead has a much greater density than the
feathers. Density is the mass per unit volume of a
substance. To find the density of a substance divide the
mass by the volume.
The amount of matter in an object is its mass. Consider
the matter in a bag of potatoes to that of a bag of popcorn.
The bag of potatoes has more matter than the bag of popcorn.
The bag of potatoes has more mass. Mass is measured with an
instrument called a balance, in units of grams. The amount
of space an object takes up is called its volume. A
graduated cylinder is used to measure the volume of a liquid
and is often measured in milliliters. The volume of a solid
can be determined by measuring the amount of water the solid
displaces in a graduated cylinder.
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