1. Chapter 13 Forces in Fluids
It’s a bit of a review…

2. Pressure Area Pressure is force exerted over an area P = Force
Area
Pressure is measured in kilopascals (kPa), Remember?

3. Pressure
If a weightlifter exerts 30,000 Newtons of force on a barbell 3.5m2, what is the resultant Pressure?
P = F / A
= 30,000N / 3.5m2
= kPa

4. Water Pressure Water pressure increases with depth
Pressure in a fluid at any given depth is constant, and is exerted equally in all directions

5. Air Pressure Air is a mixture of gases that has mass
The weight of the earth’s atmosphere exerts a pressure of 101kpa at sea level
You cannot feel this pressure because your body is used to it, but if you were on another planet, you’d notice a change

6. Planetary Atmospheric Pressures

7. Air Pressure
Air pressure decreases with altitude: the higher up you go, the less air there is, and the less pressure it exerts
This is why mountain climbers need oxygen – there is not enough air to breath at that altitude

8. Air Pressure
The weight of the atmosphere above you is exerting a force of 1000N at all times
Your body has a similar pressure which balances out the force of the atmosphere
Ever have your ears pop?

9. Pascal’s Principle
The pressure applied to a fluid is transmitted unchanged throughout the fluid.
When you squeeze one end of the tube, the pressure is transmitted through the entire fluid, and the paste will pushed out of all openings.

10. Bernoulli’s Principle
States that as the velocity of a fluid increases, the pressure exerted by that fluid decreases.
Airplane wing

11. Bernoulli’s Principle

12. Buoyancy
Is the ability of a fluid (liquid or gas) to exert an upward force on an object immersed in it.
This upward force is called the buoyant force Force of the object pushing down on the water.
Buoyant force of water pushing up on the object.

13. Buoyant Force
The amount of buoyant force determines if an object will sink or float.
If the buoyant force is less than the object’s weight, it will sink. If the buoyant force is greater than the weight, it will float.

14. Archimedes's Principle
States that the buoyant force on an object in a fluid is equal to the weight of the fluid displaced by the object.
Same mass of steel
Ship hull
Since hull displaces more water, the buoyant force is greater. It floats.