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13.2 Forces and Pressure in Fluids
How does Pascal’s principle describe the transmission of pressure through a fluid?
Transmitting Pressure in a Fluid
According to Pascal’s principle, a change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid.
13.2 Forces and Pressure in Fluids
Pascal’s Principle
A.The forces exerted against the walls of the container are equal at a given depth.
B.When squeezed, the pressure is transmitted equally throughout the fluid.
Transmitting Pressure in a Fluid
13.2 Forces and Pressure in Fluids
At any given depth, equal pressures act against all points on the inside of the bottle.
When the bottle is squeezed, the pressure still increases with depth. The pressure increases equally throughout the water.
Transmitting Pressure in a Fluid
13.2 Forces and Pressure in Fluids
How does a hydraulic system work?
A hydraulic system is a device that uses pressurized fluid acting on pistons of different sizes to change a force.
Transmitting Pressure in a Fluid
In a hydraulic lift system, an increased output force is produced because a constant fluid pressure is exerted on the larger area of the output piston.
Hydraulic Systems
13.2 Forces and Pressure in Fluids
The truck uses hydraulic-powered struts to lift its load. The larger area of the output piston produces the increased force.
Transmitting Pressure in a Fluid
13.2 Forces and Pressure in Fluids
When an input force is applied to the small piston in a hydraulic system, the piston pushes against the fluid sealed in the system.
• The pressure produced by the small piston is transmitted through the fluid to the large piston.
• The pressure on both pistons is the same.• Because the output pressure acts on a much
larger area, the output force is larger.
Transmitting Pressure in a Fluid
13.2 Forces and Pressure in Fluids
How is the speed of a fluid related to the pressure within the fluid?
Bernoulli’s Principle
According to Bernoulli’s principle, as the speed of a fluid increases, the pressure within the fluid decreases.
13.2 Forces and Pressure in Fluids
Try this simple experiment. • Hold a sheet of paper by its top corners. • Position the paper directly in front of your
mouth.• Blow over the top surface of the paper.• The far end of the paper lifts upward.
Bernoulli’s Principle
13.2 Forces and Pressure in Fluids
As the air blows across the top of the paper, the pressure exerted by the air decreases.
• The motionless air below the paper exerts a greater pressure.
• The difference in pressure forces the paper upward.
Bernoulli’s Principle
13.2 Forces and Pressure in Fluids
The fast-moving stream of air from the blow dryer creates a column of low-pressure air.
The table tennis ball is suspended in an area of low pressure.
13.2 Forces and Pressure in Fluids
Wings and Lift
Bernoulli’s principle explains the ability of birds and airplanes to fly.
• Air traveling over the top of an airplane wing moves faster than the air passing underneath.
• The pressure difference between the top and the bottom of the wing creates an upward force known as lift.
Bernoulli’s Principle
13.2 Forces and Pressure in Fluids
Air flowing over the top of the wing is diverted up and over the wing’s curved surface.
Bernoulli’s Principle
13.2 Forces and Pressure in Fluids
The wings of birds produce lift in much the same way as an airplane wing. Unlike airplane wings, birds can flap their wings to produce forward movement and some lift.
The downward force created by the spoiler on a race car pushes the tires down onto the road, giving the car better traction.
Bernoulli’s Principle
13.2 Forces and Pressure in Fluids
Spray Bottles
Pressure differences between the solution chamber and the moving stream of water draw the solution into the stream.
Bernoulli’s Principle
13.2 Forces and Pressure in Fluids
Assessment Questions
2.A 5-N input force of a hydraulic system corresponds to a 40-N output force. If the area of the small piston is 11 cm2, what is the area of the large piston?
a.8 cmb.255 cmc. 88 cm2
d.2200 cm2
13.2 Forces and Pressure in Fluids
Assessment Questions
2.A 5-N input force of a hydraulic system corresponds to a 40-N output force. If the area of the small piston is 11 cm2, what is the area of the large piston?
a.8 cmb.255 cmc. 88 cm2
d.2200 cm2
ANS: C
13.2 Forces and Pressure in Fluids
Assessment Questions
•According to Bernoulli’s principle, as the speed of a moving fluid increases, the pressure within the fluid increases.
TrueFalse
13.2 Forces and Pressure in Fluids
Assessment Questions
•According to Bernoulli’s principle, as the speed of a moving fluid increases, the pressure within the fluid increases.
TrueFalse
ANS: F, decreases
