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.

Equation for Density

=mV

density= massvolume

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

P= FA

pressure=force area

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?

Why Do Ships Float?

The trick is to get the iron to displace more water by shaping it like a bowl.

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

Bernoulli's Principle

Air must flow faster over the top of the airplane wing. According to Bernoulli, the

pressure there must become less.

A lifting force is generated that tries to

push the wing up toward the area of lower

pressure.

lift

drag