DensityDensity is how concentrated or compact
matter is.
Packing snow into snowballs increases
its density.
You are squeezing large
amounts of matter into small
volumes of space.
Changing the DensityYou can make an object denser without
adding any any mass (or weight) by squeezing it into a smaller space.
When the volume of a loaf of bread
is reduced, its density
increases.
Density of Water
A liter of water occupies a volume of 1000 cm3 and has a
mass of 1 kg.
Its density is 1 kg/L.
No matter how much water you have, its density is the same.
Float or Sink?
Any substance that is less dense than water will float in water. If the substance's density is greater than water's density, then it will sink.
The density of ice is 0.92 g/cm3.
The density of liquid water is 1.0 g/cm3.
Therefore, ice should float in water.
Pressure
Although the weight of both books is the
same, the upright book exerts a
greater pressure against the
surface of the table.
Pressure in a LiquidLiquid pressure = weight density x depth
The deeper you go underwater, the greater
the pressure.
Why is this water tower so high above
the ground?
Pressure in a Liquid
depth
Having a great “depth” of water
above the ground helps insure that
reliable water pressure is
supplied to the many homes it
serves.
Pressure Behind a DamThe average water pressure acting against the dam depends on the average depth of the water
and not on the volume of water held back.
Which dam must be built stronger?
Buoyancy in a Liquid
The greater pressure against the
bottom of the submerged rock
produces an upward buoyant force.
Even objects that are dense enough to sink will have a buoyant force exerted on them
when underwater.
Archimedes' Principle
An immersed body is buoyed up by a force equal to the weight of the fluid it displaces.
When a stone is submerged, it
displaces a volume of water equal to the
volume of the stone.
Will the buoyant force on the stone be
enough to keep it from sinking?
Archimedes' Principle
Yes, if the object is less dense than water.
A floating object displaces a
weight of fluid equal to its own
weight.
Why does some of the block of wood stick up
above the water's surface?
Archimedes' Principle
For objects that sink, the buoyant force on them is not great enough to support their entire weight.
Why Do Ships Float?
Iron is nearly 8 times denser than water.A solid bar of iron sinks straight to the
bottom of any container of water.
So why do ships that are made of
iron float?
Flotation
Additional weight or cargo requires that additional water be displaced.
This results in a larger buoyant force that is needed to support that extra weight!
The Lava Lamp
Wax at the bottom is heated by the lamp, expands, becomes
less dense and floats to the top.
Wax at the top now cools down, contracts,
becomes more dense, and sinks. heat source
Pressure in a Gas
The overall effect of millions of gas molecules colliding with each other is what we
call pressure.
When you pump more air into a tire, you increase the
density, making collisions between molecules more likely. This increases the
pressure.
Fluid Flow
Because the flow is continuous,
water must speed up when it flows
through the narrow part of the brook.
Bernoulli's PrincipleWhere the speed of a fluid increases,
internal pressure in the fluid decreases.
Water speeds up when it flows into the narrower part of the pipe.
The bubbles are bigger in the narrower part because internal pressure there is less.
faster
less pressure
slower
more pressure