1. Chapter 11 Notes
Forces in Fluids

2. Section 1 - Pressure
Pressure decreases as the area over which a force is distributed increases.
increase surface area, decrease pressure
ice skates
Pressure - equal to the force exerted on a surface divided by the total area over which the force is exerted.
Pressure = force/area
pressure units = pascal
1 Pa = 1N/m2
Chapter 11

3. Pressure cont’d fluid - substance which can easily flow
All of the forces exerted by the individual particles in a fluid combine to make up the pressure exerted by the fluid.
Balanced pressure - air pressure
as elevation increases, air pressure decreases
water pressure increases as depth increases
Chapter 11

4. Section 2 - Floating and Sinking
Buoyant force - acts in an upward direction, against the force of gravity.
Makes an object feel lighter
Archimedes’ principle - the buoyant force on an object is equal to the weight of the fluid displaced by the object
floating and sinking - pg. 383
Chapter 11

5. Floating & Sinking cont’d.
density = mass/volume units g/mL or g/cm3
water density = 1 g/mL pg.363
By comparing densities, you can predict whether an object will float or sink in a fluid.
Chapter 11

6. Section 3 – Pascal’s Principle
Pascal’s principle - When force is applied to a confined fluid, an increase in pressure is transmitted equally to all parts of the fluid.
Page Demonstration
Chapter 11

7. Hydraulic System
Multiplies a force by applying the force to a small surface area. The increase in pressure is then transmitted to another part of the confined fluid, which pushes on a larger surface area.
Small force over small area results in a larger force exerted by a larger area at another place.
Car brakes, repair shop lift, fire truck ladder
Chapter 11

8. Section 4 - Bernoulli’s Principle
Wright brothers
Fluid naturally flows from an area of hogh pressure to an area of low pressure.
Chapter 11

9. Bernoulli’s principle
As the speed of a moving fluid increases, the pressure within the fluid decreases.
Air moves at different speeds above and below objects.
Difference in pressure causes lift or downward force
wings pg. 395
Chapter 11

10. Chapter 11 - Vocabulary List
Pressure
Pascal’s principle
hydraulic system
buoyant force
Archimedes’ principle
Bernoulli’s principle
Chapter 11

11. Bernoulli’s Principle cont’d.
Bernoulli’s principle helps explain how planes fly. It also helps explain why smoke rises up a chimney, how an atomizer works, and how a flying disk glides through the air.
Chapter 11