1. IPC B Module 3 What two fluids are present in this background picture?
Forces in Fluids
IPC B Module 3
What two fluids are present in this background picture?

2. Pressure Pressure is the force that acts on a unit area of surface
Pressure = Force/Area
Remember that Area = L x w
Area is indirectly proportional to the pressure, thus pressure decreases with increase in area and increases with decrease in area.

3. Example
School bags have broad shoulder straps. Because of broad shoulder straps, the pressure because of the weight of the school bag is distributed over a larger area and it becomes easier to carry the bag.

4. Units of Pressure The SI unit of pressure is the Pascal (Pa)
1 kiloPascal (kPa) is equal to 1000 Pa
Older units include psi (pounds per square inch) used in your tires, atm (atmospheres), torr, and mmHg

5. Review Gases and Liquids are both FLUIDS
Similar to solid, liquid and gas also exert pressure. Liquid and gas exert pressure on inner walls of the container in which they are kept.
We do not feel the atmospheric pressure over us because the pressure inside our body cancels the atmospheric pressure.

6. Pressure in Fluids Water pressure increases as depth increases
The pressure in a fluid at any given depth is constant and is exerted equally in all directions.

7. Air Pressure Air pressure decreases as altitude increases.
That means it’s actually harder to cook in low pressure/high altitude.

8. Transmitting Pressure in Fluids
Pascal’s Principle-a change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid.
Forms the basis of hydraulics.
A hydraulic system is a device that uses pressurized fluid acting on pistons of different sizes to change a force.

9. Pistons Review the animation at this link
The pressure on both pistons is the same.
The FORCE can be multiplied and it’s based on the AREA

10. Bernoulli’s Experiment
Try this simple experiment. Pick up a single sheet of paper and hold its top corners using both of your hands. Now position the paper directly in front of your mouth and blow as hard as you can over the top surface of the paper. Even though you are blowing over its top, the far end of the paper lifts upward.

11. Bernoulli’s Principle
As the speed of a fluid increases, the pressure within the fluid decreases.
NOTE: This is an inverse relationship!
Things move from HIGH pressure to LOW pressure
So things will move to fill in a low pressure area.

12. Lift
The ability of birds and airplanes to fly is largely explained by Bernoulli’s principle. The air traveling over the top of an airplane wing moves faster than the air passing underneath. This creates a low-pressure area above the wing. The pressure difference between the top and the bottom of the wing creates an upward force known as lift. The lift created in this way is a large part of what keeps the airplane aloft.

13. Buoyancy
According to Archimedes’ principle, the buoyant force on an object is equal to the weight of the fluid displaced by the object.
The upward force on an object immersed in a fluid enabling it to float (or appear to be lighter)
Why you feel lighter in water than you do on land (and why it is easier to float in salt water than fresh water)

14. Buoyant Force If an object floats, it is BUOYANT
The object displaces more water than the object weighs
If an object sinks, it LESS BUOYANT
The object displaces less water than the object weighs
If an object does not sink completely to the bottom but is underwater, it has NEUTRAL BUOYANCY
The object displaces water that is equal to its weight

15. Archimedes’ Principle & Buoyancy
Because the weight of the displaced water is greater than the weight of box, the box will float to the surface of the liquid until the box displaces an amount of water equal to its weight.
Weight of Box = 2 kg
Volume = 2500 cm3
Weight of Water Displaced = 2 kg Volume of Water Displaced = 2000 mL

16. Archimedes’ Principle & Buoyancy
What Object Does in Fluid
Density (Object vs. Water)
Volume
(Object vs. Displaced Water)
Mass
(Object vs. Displaced Water)
Diagram
Floats Near the Top (Buoyant)
VO > VW
MO = MW
DO < DW
Neutrally Buoyant - Doesn’t Sink or Float
DO = DW
VO = VW
MO = MW
Sinks (Less Buoyant)
DO > DW
VO > VW
MO > MW

17. Floating and Sinking Ex.:
A ship made of steel can float because it can displace more water than the ship weighs
A steel block does not push enough water out of the way to keep it afloat
Steel
Steel Block
Higher Density
Sinks
Steel Ship
Lower Density
Floats

18. Which object(s) have a greater weight than the buoyant force. Equal to
Which object(s) have a greater weight than the buoyant force? Equal to? Less than?

19. Writing in Science Graded Separately Compare and Contrast
Write a paragraph comparing the forces acting on an object that floats in water and an object that sinks in water. Be sure to describe the relative sizes of the forces acting on each object. To explain a floating object, you could state that the weight of the floating object is equal to the buoyant force acting on it. To explain a sunken object, you could state that the weight of the sunken object is greater than the buoyant force acting on it.