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FORCES AND FLUIDS
Some things to bring out of the recesses of your mind:
Fluids: any matter that has the ability to flow = liquid
gas
Force: any push or pull exerted on matter
Pressure: force exerted on matter by air molecules
more air molecules=more pressure
less air molecules = less pressure
Let’s not forget DENSITY!!!
Density is the amount of matter in a given volume
DOES NOT CHANGE WITH CHANGES IN SHAPE
OR SIZE!!!
Density of water is 1 g/ml
The ability of an object to float is dependent on the
Object’s density with respect to the density of the
Fluid it is in.
If an object sinks, its density would be greater than the
Density of the fluid. In this case, greater than 1 if we
Are placing the object in water.
Styrofoam
D=0.75g/ml
If an object has a density greater than 1 g/ml it will sink in water.
Rock has a density
Of 3 g/ml
Pressure is a result of the presence of molecules.
Pressure of a fluid has two properties:
1. pressure is exerted perpendicular to the surface
of the object
2. pressure increases as molecules increasethe deeper you go the greater the pressure
Perpendicular force
Perpendicular forces applied to the object by the water, keep the
Object afloat. The more force applied, the easier it is to float.
The smaller the
Surface area of
The object, the
More likely it will
Sink.
Buoyancy is the force exerted on an object
by a fluid and it usually acts against gravity.
This is why objects feel lighter in water.
Some of the force of gravity (weight) is
cancelled out by the force of buoyancy. If
the buoyant force is stronger than the force
of gravity, the object will float in the fluid.
Force exerted downward (mass + gravity) is less than force exerted
By water upward (buoyant force)
Buoyancy is a factor of:
Gravity
Mass
Density of: boy
tube
water
Gravity
Buoyant Force
Archimedes’ Principle states that the
buoyant force of a fluid is equal to the weight
of the fluid displaced by the object. If an
object can displace (push away) enough
fluid to equal its weight, it will float. This is
why a tremendous ship made of iron can
float but a cannonball would sink. The ship’s
shape allows it to push enough water away
to equal the weight of the ship.
5.0
Pounds
Buoyant force is greater than the
force of gravity. Density of the
object is less than the density of
the fluid.
0.0 lbs
3.0
As with buoyancy, Archimede’s principle involves the
densities of both the fluid and the object. If density is
less than the liquid, the object floats – more than the liquid
the object sinks.
The amount of fluid displaced by the object is again
determined by how the fluid exerts pressure on the object.
If the object has a greater density than the fluid it will sink
10.0
Pounds
Density of the object is greater
than the density of the fluid.
Buoyant force is less than force
of gravity
0.0
10.0
lbs
The amount of water that was displaced by the
floating boat weighs the same as the boat itself.
According to Archimedes’ Principle, this is why
the boat floats and doesn’t sink.
Displaced Water
Bernoulli’s principle: if molecules are what cause
pressure on an object, if we remove the molecules
then we remove the pressure of the fluid exerted
on objects!
Fewer molecules here
=less pressure
More molecules here
= more pressure
Pascal’s principle: the pressure exerted on a confined
fluid is dispersed equally throughout that fluid as well
as on the walls of the container.
Because the compression of the gas is distributed evenly on the
confined liquid, the resulting action is equal.
Because Pascal’s law says that the pressure on a confined fluid is
dispersed evenly throughout the fluids involved, this pressure will directly
affect density and therefore buoyancy.
Pressure on a fluid disperses a force proportionate to
the number of molecules and therefore amount of pressure
present.
Fewer molecules here = less
pressure (less force) so water
does not go as far.
More molecules here=more
pressure (more force) so water
is pushed farther away.