Why is the electricity produced at the bottom of dams?

Why is the electricity produced at the bottom of dams? When you catch a deep-sea fish, why does its eyes pop-out? Why do your ears pop on an airplane or up in the mountains?

Forces in Fluids

Pressure • Pressure is equal to the force applied to a surface, divided by the area.

Equations for Pressure • Pressure = Force/surface area • Pressure = Newtons (Kg x m/s/s) side x side • Units are in Pascals or N/m²

Fluid • A substance that can easily change its shape, such as liquids and gases. • The molecules in a fluid have a certain amount of force (mass and acceleration) and exert pressure on surfaces they touch.

FLUID PRESSURE • All the molecules add up together to make up the force exerted by the fluid.

Air has a mass of 1Kg/m³ AIR PRESSURE • Gravity creates an air pressure of 10.13N/m³ at sea level.

1 atmosphere = 760 mmHg = 29.92 inHg = 14.7 lb/in2 = 101.3 KPa

Pressure and Elevation • Air Pressure decreases as elevation increases.

The whole system is a low pressure, but it dramatically decreases towards the eye of the hurricane. Very Low pressure Pressure always flows from high to low, which creates the high velocity winds. Higher Pressure

Barometric Pressure • The barometer is used to forecast weather. • Decreasing barometer means stormy weather and an increasing barometer means warmer weather.

Pressure and Depth • Water pressure increases with depth.

Pressure and Temperature • As temperature increases, pressure increases.

Pascal's Principle • When a force is applied to a confined fluid, the increase in pressure is transmitted equally to all parts of the fluid.

Transmitting Pressure in a Fluid • When force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.

Buoyancy The tendency or ability of an object to float.

Buoyancy • The pressure on the bottom of a submerged object is greater than the pressure on the top. The result is a net force in the upward direction.

Buoyant Force The upward force exerted by a fluid on a submerged or floating object.

Buoyancy • The buoyant force works opposite the weight of an object.

Archimedes’ principle: • Buoyant Force on an object immersed in a liquid equals the weight of the liquid displaced.

Density and buoyancy: An object that has a greater density than the fluid it is in, will sink. If its density is less than the fluid it will float. Density

A solid block of steel sinks in water. A steel ship with the same mass floats on the surface.

Density • Changes in density cause a submarine to dive, rise, or float.

DENSITY OF WATER 1g/cm³

Bernoulli's Principle

Bernoulli's Principle • The pressure exerted by a moving stream of fluid is less than its surrounding fluid.

Bernoulli's Principle • Therefore, as the speed of the fluid increases its pressure decreases.

This is the reason planes fly.

There are 4 forces in flight • Thrust- jet engines and propellers create lift which moves the plane forward. • Drag- air friction which must be overcome for the plane to fly. • Weight- pulling the plane down. • Lift- raises the plane.

Bernoulli’s principle explains how lift is created. • Faster moving air has less pressure. • The shape of the wing makes the air move faster over the top, creating lift to make the plane rise.

Others appeal to a model based on Newton's laws and assert that the main lift comes as a result of the angle of attack. Part of the Newton's law model of part of the lift force involves attachment of the boundary layer of air on the top of the wing with a resulting downwash of air behind the wing. If the wing gives the air a downward force, then by Newton's third law, the wing experiences a force in the opposite direction - a lift. While the "Bernoulli vs Newton" debate continues, Eastlake's position is that they are really equivalent, just different approaches to the same physical phenonenon. NASA has a nice aerodynamics site at which these issues are discussed.

That's All Folks!!

Why is the electricity produced at the bottom of dams?