1. Forces in Fluids

2. Pressure The force distributed over an area Pressure = Force/Area Unit: the Pascal (Pa) 1 Pa = 1 N/m 2

3. Pressure in Fluids A fluid can take the shape of its container The moving particles exert force on the walls of the container. Water pressure increases with depth and is exerted in all directions.

4. Air Pressure and the Atmosphere Air pressure decreases as you increase altitude. Why? The atmosphere exerts a pressure of about 101 kPa at sea level. This equal to about 15 psi (pounds per square inch)! So, why aren’t we being crushed by the air?

5. Earth’s Atmosphere 78% Nitrogen 21% Oxygen 1% Argon Trace gases

6. Measuring Air Pressure Mercury Barometer invented by E. Torricelli in 1643 A glass tube inverted into a pool of mercury Aneroid Barometer Uses a box and coil spring mechanism to measure changes.

7. Pascal’s Principle A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid.

8. Hydraulic Systems Increase output force due to pressure remaining constant.

9. Bernoulli’s Principle As the speed of a fluid increases the pressure within the fluid decreases. Daniel Bernoulli 1700-1782 Switzerland

10. Wings at Work Lift Weight Thrust Drag

11. Buoyant Force Buoyancy is the ability of a fluid to exert an upward force on an object placed in it. This results in the apparent lost of weight for the object. The buoyant force is the upward force caused by the fluid.

12. Archimedes Principle The buoyant force is equal to the weight of the fluid displaced by the object. The larger the volume of the object – the larger the buoyant force The denser the fluid the greater the buoyant force.

13. Density and Buoyancy If the object is less dense than the fluid it is placed in then it will float. If the object is more dense than the fluid it is placed in then it will sink. If the buoyant force is less than the weight of the object then it will sink.

14. Buoyancy Positive buoyancy – Buoyant force > weight – float Negative buoyancy – Buoyant force < weight – sink Neutral buoyancy – Buoyant force = weight – suspended