Density:
Another Property of Fluids
307- 10 describe situations in daily life where the density of
substances naturally changes or is intentionally altered.
307-8 describe the relationship between the mass, volume
and density of solids, liquids, and gases using a particle
model of matter
208-2 Identify questions to investigate from practical
problems involving floating, sinking and density
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We have all seen the effects of a spill from an oil
tanker.
Luckily, oil floats, so we are able to clean it up
easier.
Why does oil float?
What is density?
Density is the mass per unit volume of
substance (the amount per unit size).
Density is a characteristic physical
property of liquids, solids and gases.
It is expressed as grams per cubic
centimeter (g/cm3), kilograms per
cubic meter (kg/m3) or grams per
milliliter (g/ml).
When we speak of items being heavy or light, we
really mean that one has a higher density than the
other.
For example: The rock is denser than the floating
cork.
How is density calculated?
Density is calculated by dividing the mass of a
substance by its volume.
D = M/V
Density in the real world
So, why does oil float on water?
Oil floats on water because it is less dense than
water.
If you poured about 15ml of cooking oil into a basin of water
you would notice the oil sinking into the water, then rising
and spreading out over the surface and finally stabilizing into
several oval shapes.
This is similar to what happens when oil leaks from a
tanker into the sea.
Because the oil is less dense than water, it floats on the
surface. The lighter the oil , the faster is will spread,
making it harder to contain. Once the leak is
contained, recovery of the oil is the next step.
What are three ways oil can be
recovered after a spill in the ocean,
lake or river?
The three ways are :
1. skimmers
2. sorbents
3. dispersants
What are skimmers?
Skimmers are boats and other devices that can remove oil
from the sea surface before it reaches sensitive areas along a
coastline. In the photo at right, oil is being skimmed from the
sea surface. Two boats are towing a collection boom, while oil
concentrated within the boom is being picked up by the
skimmer (the vessel at the apex of the boom).
What are Sorbents?
Sorbents are materials that soak up liquids. They can be used to
recover oil through the mechanisms of absorption, adsorption,
or both. The act as sponges to draw up the oil slick.
What are dispersants?
Dispersants are special chemical detergents which
attach themselves to the oil molecules and break up the
spill.
How can oil be recovered after an
oil spill?
http://video.nationalgeographic.
com/video/player/news/environ
ment-news/nsf-oilsomasundaran-vin.html
Understanding Concepts
Make a list of solids that you
know will float on water.
The solids that will float on water are balsa
wood, pine wood, birch wood and ice
List all of the gases that will float on
air.
The gases that will float on air are hydrogen and
helium
Why does Helium float on air?
Helium floats on air because it is
less dense than air
Aerial daredevil Mike Howard
flies to 7,000 feet attached to
300 small balloons.
Independent Assessment
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A solid block of iron sinks in water, but a ship
made out of iron floats, explain why this can
happen.
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Then, take a piece of plasticine and mold it into
a shape that you think would float. Explain your
design and why you think it can float.