13.2 Forces and Pressure in Fluids

Transmitting Pressure in a Fluid The pressure in a fluid at any given depth is constant, and it is exerted equally in all directions So if I squeeze a water bottle, will the pressure be greater at the point where I squeeze?

Transmitting Pressure in a Fluid Pascal’s Principle According to Pascal’s principle, a change in pressure at any point in a fluid is transmitted and unchanged in all directions throughout the fluid

Transmitting Pressure in a Fluid 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: Hydraulic systems Hydraulics is the science of applying Pascal's principle 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: Hydraulic systems 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. 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: Hydraulic systems If you are working with a hydraulic system where the large piston has 8 times the area of the small piston, then the output force is how many times larger? 8 times. Why is this? Recall that force is equal to the product of pressure and area. Because the pressure on each piston is the same, the difference in forces is directly related to the difference in areas.

Bernoulli's Principle Swiss scientist Daniel Bernoulli (1700–1782) As the speed of a fluid increases, the pressure within the fluid decreases.

Bernoulli's Principle How does an airplanes wings work? The wings of an airplane are shaped so that the air going over the top of the wing goes faster than the air on the bottom. More speed on top means less pressure on top, which means we get lift.

Bernoulli's Principle Lift: an upward force due to a pressure difference between the top and bottom of a wing Air flowing over the top of the wing is diverted up and over the wing’s curved surface.

Bernoulli's Principle 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.

Bernoulli's Principle Spray Bottles Pressure differences between the solution chamber and the moving stream of water draw the solution into the stream. As water streams through the sprayer, it passes over the top of a small tube that reaches down into the solution chamber. The fast-moving water creates a low-pressure area at the top of the tube. The pressure difference between the solution chamber and the tube forces the concentrated solution up the tube. The solution then mixes with the water and is sprayed out of the end of the sprayer.