Pressure in Fluids • Pressure depends on force and area. • If you spread the force over more area, there is less pressure. Which creates more pressure? 10 cm 10 cm 20 N Push 5 cm 5 cm 20 N Push If this woman were to step on you, which part of the shoe creates more pressure? Force (weight) Force (weight) Area Same force over smaller area creates more pressure under the heel. Pressure in Fluids • Pressure depends on force and area. • If you spread the force over more area, there is less pressure. • The formula to calculate pressure is: Pressure = force area The S.I. unit that we use for pressure is the pascal (Pa) What causes fluid pressure? • Pressure in fluids is caused by the particles pushing against a surface. • Each particle gives a teeny tiny push, but they all add up. • The more crowded the particles are, the harder they push. • The faster they are moving, the harder they push. Less Fluid Lower Pressure More Fluid Higher Pressure Is Because air has weight, and if there is less air above you, there then lessthere pressure more pressure will be or less weight. Why? the causes mountain? The weightonoftop theoffluid the pressure! Plastic bottle sealed at 14,000 feet on Mauna Kea observatory on the island of Hawaii, taken down to 9000 feet and then 1000 where the air pressure is crushing the bottle. You can’t feel If the air has weight, why atmospheric pressure your don’t because we feel the body fluids push back! atmospheric pressure? The forces are balanced. Less Fluid More Fluid Because water has weight, and if there is more water above you, Is there more pressure then there will be more weight. How you on the do divers or theknow? shark? The weight of the fluid causes the pressure! What part of an iceberg has the most pressure on it? Pressure increases as you get deeper! Remember that pressure pushes in all directions so the iceberg is being pushed on all sides, all the way around.