Section 3 Behavior of Fluids

I. Pressure Why the tyre of bike, the airbed and basket ball can be firm to work?

The firmness is the result of ___________________________. These particles collide with the ___________ and push the surface __________.

When the tyre or ball are flat, what can you do to resume firmness? ______ particles, stronger force.

Pressure = Pressure is equal to the force exerted on a surface divided by the total area over which the force is exerted. Unit: For a given area, pressure ________ as force increases. For a given force, pressure _________ as area decreases.

Compare the pressure of A and B applied on the desk. A B cubeweightarea A200 N25cm 2 B600 N100cm 2 (Don ’ t think heavier object always exert more pressure!)

II. Atmospheric Pressure The atmosphere is the We live at the bottom of the “ air sea ”. 1. Atmospheric Pressure

Seawater exert pressure on diver The air around also press force on you.

101.3 kPa = _________ Pa = _________N/m 2 __________________ is the pressure of air. At sea level, atmospheric pressure is ________ So the force on 1 m 2 is N which is about the weight of the truck!

You don’t notice but you take advantage of air pressure. cleaner drink from a straw

2. Balanced Pressure The force exerted on the desk is about the weight of the truck! The desk isn ’ t be crushed because _____________ ___________________ _________________

With air inside, the iron pail will not be crushed. Without air, the iron pail will be crushed.

Atmosphere exerts a pressure on all surface of our body. ____________ in your body exert a pressure that balance the atmosphere pressure.

3. Variations in Atmospheric Pressure In 17th century, French physician Pascal had a experiment. A balloon partially filled with air expanded while being carried up the mountain.

____________________ ____________________ ____________________ As altitude increases, the number of air particles ________, so the atmosphere exert _____pressure on the balloon.

4. Air Travel Travel to higher altitudes, you might feel a popping sensation in your ears. To ________air, your ear is heard as a pop.

III. Changes in Gas Pressure The pressure of a gas in a closed container changes with ________ and ___________.  ________volume, more pressure. The particles have __________ to move, so they collide _____ _______ and produce ________pressure.

The particles have ______ kinetic energy to move, so they collide ___________ and thereby produce a ________ pressure.  ________ temperature, more pressure

IV. Float or Sink Water pressure _________ as you swim deeper in water. Atmospheric pressure __________ as you walk down a mountain.

________ force ________force The difference in pressure results in an upward force—— _________________

Archimedes’ Principle The buoyant force on an object is equal to ________________ _________________________ _________________________. The buoyant force on object =

Buoyant force weight Buoyant force= weight, _________ Buoyant force < weight, __________ Buoyant force > weight, __________________

Density=

A tourist is floating on Dead Sea. The Dead Sea dissolved __________ so that its density is ______than the man ’ s density.

Why an iceberg can float on water? Because ______________ ____________________ ________________. For most matter, D solid > D liquid But _____ is exception!

How to make a balloon float in air? (1) (2)

Why the steel ship can float on water even the density of steel is much greater than water?

Archimedes' Principle explains why steel ships float. ______________________________________ ______________________________________ _____________________________________.

Example: A 4.60 cm 3 sample of a solid has a mass of 10.0g. Will it float in water? (density of water is 1.00g/cm 3 )

V. Pascal’s Principle When a force is applied to a confined fluid, __________________________________ __________________________________. force water The pressure increases equally everywhere

Application of Pascal’s Principle Hydraulic system use Pascal’s principle to ____________, which enable up to lift heavy objects using __________________. Force= pressure ×area Downward force=500 N Upward force=10,000 N

Ex: A hydraulic device has two pistons. How much force do you have to apply to the piston with an area of 10 cm 2 to lift an object weighting 2,000 N on a piston with an area of 50 cm 2 ? ? N 10 cm N 50 cm 2

Force pump Fluid in a closed container which has a hole will __________________________ ________________________________.

In heart, ______________ work together to move blood to and from the lungs and to the rest of the body. Blood from the body Blood to lungs Blood from lungs Blood to body

1.Which change results in an increase in gas pressure in a sealed, flexible container? A) Decrease in temperature. B) Decrease in volume. C) Increase in volume. D) Increase in altitude. 2. Which is a unit of pressure? A) N B) kg C) g/cm 3 D) N/m 2 Learning Check

3. In which case will an object float on a fluid? A) Buoyant force is greater than weight. B) Buoyant force is less than weight. C) Buoyant force equals weight. D) Buoyant force equals zero. 4. Which is equal to the buoyant force on an object? A)Volume of the object B)Weight of the displaced fluid C)Weight of object D)Volume of fluid

A king ’ s crown has a volume of 110 cm 3 and a mass of 1800 g. The density of gold is 19.3 g/cm 3. Is the crown pure gold? Calculation