Download what forces act on the block?

Main Ideas
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Forces Within Solids
Forces within solids
Pressure
Buoyant forces: Archimedes Principle
Floating objects
Forces within the earth’s crust: isostasy
Convection
Chunk inside wall
Building
Contact Forces
Weight
Pieces of solid objects must have internal contact
forces equal to their weight.
what forces act on the block?
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significant gravitational force?
charges involved?
is anything touching the object
(contact forces)?
a. normal force
b. friction
what is the motion of the block?
acceleration = 0
net force = 0
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Frightened Fish
What laws and principles apply?
Pressure
Shark
Fish
the contact forces and gravity act
equally on the block
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Fish
contact force
acceleration
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Pressure=Force/Area
Pressure of a static fluid is perpendicular to
surfaces immersed in the fluid
Pressure of fluid is the same in all directions
Pressure increases with depth
Pressure is the same for all points at the
same depth
weight
PS100, Section 3, Winter 2000
Chapter 6, Page 1
Atmospheric and Hydrostatic
Pressure
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Atmospheric
pressure at the
earth’s surface is
about 15 psi.
Buoyant Forces
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Fluids always push up on anything
they surround.
Two ways of thinking about it:
1.
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Water pressure is
about 1 atmosphere
every 11 meters.
2.
United States Department of the Interior
Bureau of Reclamation - Lower Colorado Region
Archimedes Principle
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Pressure is greater on the bottom
Fluids can support their own weight.
The upward force is equal to the weight
of the displaced fluid.
Immersed Object
An object immersed in a fluid
experiences an upward buoyant force
due to contact interactions with the
surrounding fluid, whose strength is
equal to the weight of the displaced
fluid.
Contact Forces
Gravity
Three Immersed Balls
Gravity
Floating Objects
buoyant force
lead
water
cork
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weight
PS100, Section 3, Winter 2000
According to Archimedes Principle, an object will sink
until its weight equals the weight of displaced fluid.
Chapter 6, Page 2
Brain twister
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Iceberg Example
So, how much water does it take to
float a battle ship?
a. A weight of water equal to the weight of
the ship.
b. A volume of water equal to the volume of
the ship.
c. A few cups.
Forces Within the Earth’s Crust
Convection
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Isostasy-balance between the weight of the earth’s
crust and buoyancy of the mantle
crust floats on mantle
taller features (mountains) have deeper roots
Ways to say something floats
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cold (high density) fluids sink
warm (low density) fluids rise
this creates circulating currents
It is less dense than the surrounding fluid.
It weighs less than an equal volume of fluid.
The buoyant force is equal to its weight
when it is only partially submerged.
It displaces a weight of fluid equal to its
weight when it is only partially submerged.
STOP!
n Remember
to read
Chapter 9
before next
class.
You must compare weight and buoyant force.
PS100, Section 3, Winter 2000
Chapter 6, Page 3