Transcript Sinking & Floating

Buoyancy
(Sinking & Floating)
Slide Show #3
The Titanic
• Dubbed “The Unsinkable”
• Hit an iceberg & sank in 1912
• Over 1500 people died.
Why is it that…..
In 2 hours and 45 minutes a huge
ship that was sailing along
became a sunken wreck?
Why does most of an iceberg lie
beneath the surface of water?
WHAT MAKES AN OBJECT FLOAT OR
SINK?
Buoyancy
• Objects under water
seem lighter.
• The pressure of
water exerts a force
called buoyant force.
Buoyant Force vs. Weight
• Buoyant Force acts in the upward direction.
• Weight acts in a downward direction.
Buoyancy Types
+ buoyancy (rises)
- buoyancy (sinks)
0 neutral buoyancy (stationary)
Displacing Water
• An object underwater
(submerged) displaces
(takes the place of ) a
fluid equal to its own
volume (how much
space it takes up).
Floating & Sinking
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There is always a downward force (weight).
If Weight > than Buoyant Force, object sinks.
If Weight < Buoyant Force, object rises.
If Weight = Buoyant force, object floats or can stay
stationary if underwater!
This dude named Archimedes…
Archimedes Principle states that the Buoyant
Force acting on an object is equal to the weight
of the fluid displaced.
Real Weight = 3 Newtons
After dunked,
Weight = 1 Newton
Buoyant Force =
3 -1 = 2 Newtons
Weight of fluid displaced
= 2 Newtons
In water…..
• The Density of water is 1.00 g/cm3
• If object’s density is < 1.0 g/cm3 (floats)
• If object’s density is > 1.0 g/cm3 (sinks)
• If object’s density = 1.0 g/cm3 (neutral)
Hydrometers
• A hydrometer measures the
density of a fluid.
• The depth to which it sinks
in a fluid depends on the
density.
Floating & Sinking in the Atmosphere
• Objects float in all fluids
• Including gases!
• Air is a good example.
Helium vs. Hot Air
Helium
• Helium is a light gas.
• It is lighter than air.
• Helium’s density < density
of surrounding air.
Hot Air Balloon
• Hot air is less dense than
cold air.
• Molecules of air move
farther apart when hot.
• More volume, less density.
• Balloon “floats”
Coke vs. Diet Coke
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•
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Coke has corn syrup
Diet Coke does not
Corn syrup is very dense.
So, Coke sinks!
Diet Coke floats!
The Ice Cube
• Ice floats on water.
(It is less dense than
water)
• Ice sinks in alcohol
(It is more dense than
alcohol)
• The Egg is
more dense
than water
(It sinks)
• The Egg is
less dense
than salt
water
(It floats)
Egg Buoyancy!
Density Column
• Densities are in order from the
lowest (at the top) to the
highest (at the bottom)
• This accounts for things like oil
skimmers and cooking with
alcohol
Hot Air Bag
• Hot Air is less dense
than colder air
around it.
• So, the hot air in the
bag makes it more
buoyant (it floats)!
Fluids experience
buoyancy as well!
• Hot fluid
moves faster!
• Hot air rises!
• Cold Fluid
moves slower.
• Cool air sinks!
And now…..
• Eureka – Buoyancy
• Eureka – Convection