Chapter 11- Forces in Fluids
CUE WORDS or QUESTIONS
What is pressure?
What is the unit for pressure?
NOTES WRITTEN
Pressure – the force exerted on a surface divided by the total area over
which the force is exerted so the amount of pressure you exert depends
on the area over which you exert a force
• Pressure = Force / Area
– Force = N
– Area = m2
– Pressure = N/m2 = Pascal (Pa)
What is a fluid?
Fluid – a material that can easily flow and takes the shape of any container
All of the forces exerted by the individual particles in a fluid combine to
•
make up the pressure exerted by the fluid.
As your elevation increases, atmospheric pressure decreases
•
Water pressure increases as depth increases
What is density?
Density – mass per unit volume
• Density = mass / volume (g/ml or g/cm3)
• The density of water is 1.0 g/ml or 1.0 g/cm3
• An object that is more dense than the fluid sinks
• An object that is less dense than the fluid floats
What is buoyant force?
The buoyant force acts in the direction opposite to the force of gravity,
so it makes an object feel lighter
Buoyant force – upward force exerted by a fluid on a submerged object
What is Archimedes’ principle?
Archimedes’ principle - the buoyant force acting on a submerged object
is equal to the weight of the fluid the object displaces
If the weight of the object is greater than the buoyant force – then the net
force will be downward and the object will sink
If the weight of the object is less than the buoyant force then the net force will
Why do boats float?
be upward and the object will float
An object with greater volume has a greater buoyant force acting on it – even
if the object is more dense than the fluid it is immersed in

SUMMARY
This is why cruise ships float… the large amount of water displaced
CUE WORDS or QUESTIONS
What is Pascal’s principle?
NOTES WRITTEN
Pascal’s principle – the pressure increases by the same amount
throughout an enclosed or confined fluid
When force is applied to a confined fluid, the change in pressure is
transmitted equally to all parts of the fluid
How do hydraulic systems
relate to Pascal’s principle?
Hydraulic system – uses liquids to transmit pressure and multiply force in a
confined fluid
The hydraulic brake system of a car multiplies the force exerted on the brake
pedal
What is Bernoulli’s principle?
Bernoulli’s principle – the pressure exerted by a moving stream of fluid is
less than the pressure of the surrounding fluid
Moving fluid creates a lower pressure– air moves from high to low pressure
How does Bernoulli’s principle
relate to airplanes?
SUMMARY
Wings can be shaped to move air faster or slower on top or bottom of the
wing, depending on if a plane needs to move up or down
Smoke goes up the chimney due to air blowing across the chimney creating
a up
lower pressure pushing the smoke upward and out of the house