States of Matter Section 3

Pressure

〉Fluids exert pressure evenly in all directions.

– pressure: the amount of force exerted per unit area of a surface

– example: when you pump up a bicycle tire, air particlesconstantly push against each other and against the tire walls

States of Matter Section 3

Pressure, continued

• Pressure can be calculated by dividing force by the area over which the force is exerted:

• The SI unit for pressure is the pascal.

– pascal: the SI unit of pressure; equal to the force of 1 N exerted over an area of 1 m2 (symbol, Pa)

, or Force F

Pressure PArea A

States of Matter Section 3

Buoyant Force

〉All fluids exert an upward buoyant force on matter.

• buoyant force: the upward force that keeps an object immersed in or floating on a fluid

States of Matter Section 3

Buoyant Force, continued

• Archimedes’ principle: the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid that the object displaces.

States of Matter Section 3

Comparing Weight and Buoyant Force

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Buoyant Force, continued

• An object will float or sink based on its density.

– If an object is less dense than the fluid in which it is placed, it will float.

– If an object is more dense than the fluid in which it is placed, it will sink.

States of Matter Section 3

Density

States of Matter Section 3

Pascal’s Principle

〉Pascal’s principle : if the pressure in a container is increased at any point, the pressure increases at all points

– Mathematically, Pascal’s principle is stated as P1 = P2.

– Because P = F/A, Pascal’s principle can also be expressed as F1/A1 = F2/A2.

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Pascal’s Principle, continued

• Hydraulic devices are based on Pascal’s principle.

– Because the pressure is the same on both sides of the enclosed fluid, a small force on the smaller area (left) produces a much larger force on the larger area (right).

– The plunger travels through a larger distance on the side that has the smaller area.

States of Matter Section 3

Fluids in Motion

〉Fluids move faster through small areas than through larger areas, if the overall flow rate remains constant. Fluids also vary in the rate at which they flow.

States of Matter Section 3

Fluids in Motion, continued

• Viscosity depends on particle attraction.– viscosity: the resistance of a gas or liquid to flow

• Bernoulli’s principle: Fluid pressure decreases as speed increases.

States of Matter Section 3

Start of Class Review Chapter 3

• All matter is made of atoms and molecules that are always in motion.

• Because they are in motion all particles of matter have kinetic energy.

• Mass and energy are both conserved. Neither mass nor energy can be created or destroyed.

• All fluids exert an upward buoyant force on matter• Fluids move faster through small areas than through

larger areas, if the rate remains constant.

States of Matter Section 3

End of Class Review Chapter 3

• You can classify matter as solid, liquid, or gas by determining whether the shape and volume are definite or variable.

• The identity of a substance does not change during a change of state.

• Fluids exert pressure evenly in all directions.• All fluids exert an upward buoyant force on matter.