FORCE AND FLUIDS !! FELIPE CASTAÑO OSORNO
The amount of force exerted on a given area is pressure.
Calculating Pressure
Pressure can be calculated by using the following equation:
Calculating Pressure
Pressure can be calculated by using the following equation:
The SI unit for pressure is the pascal. One pascal (1 Pa) is the force of one newton exerted over an area of one square meter (1 N/m2).
The atmosphere is the layer of nitrogen, oxygen, and other gases that surrounds Earth. Earth’s atmosphere is held in place by gravity, which pulls the gases toward Earth. The pressure caused by the weight of the atmosphere is called atmospheric pressure.
Atmospheric pressure is exerted on everything on Earth, including you. At sea level, the atmosphere exerts a pressure of about 101,300 N on every square meter, or 101,300 Pa. So, there is a weight of about 10 N (about 2 lbs) on every square centimeter of your body. Why don’t you feel this crushing pressure? Like the air inside a balloon, the fluids inside your body exert pressure.
The atmosphere is the layer of nitrogen, oxygen, and other gases that surrounds Earth. Earth’s atmosphere is held in place by gravity, which pulls the gases toward Earth. The pressure caused by the weight of the atmosphere is called atmospheric pressure.
Atmospheric pressure is exerted on everything on Earth, including you. At sea level, the atmosphere exerts a pressure of about 101,300 N on every square meter, or 101,300 Pa. So, there is a weight of about 10 N (about 2 lbs) on every square centimeter of your body. Why don’t you feel this crushing pressure? Like the air inside a balloon, the fluids inside your body exert pressure.
Variation of Atmospheric Pressure
The atmosphere stretches about 150 km above Earth’s surface. However, about 80% of the atmosphere’s gases are found within 10 km of Earth’s surface. At the top of the atmosphere, pressure is almost nonexistent. The pressure is close to 0 Pa because the gas particles are far apart and rarely collide. Mount Everest in south-central Asia is the highest point on Earth. At the top of Mount Everest, atmospheric pressure is about 33,000 Pa, or 33 kilo-pascals (33 kPa). (Remember that the prefix kilo- means 1,000. So, 1 kPa is equal to 1,000 Pa.) At sea level, atmospheric pressure is about 101 kPa.
Atmospheric Pressure and Depth
Take a look at Figure 3. Notice how atmospheric pressure changes as you travel through the atmosphere. The further down through the atmosphere you go, the greater the pressure is. In other words, the pressure increases as the atmosphere gets “deeper.” An important point to remember about fluids is that pressure varies depending on depth. At lower levels of the atmosphere, there is more fluid above that is being pulled by Earth’s gravitational force. So, there is more pressure at lower levels of the atmosphere.Water Pressure and Depth
Like atmospheric pressure, water pressure depends on depth. Water pressure does not depend on the total amount of fluid present. A swimmer would feel the same pressure swimming at 3 m below the surface of a small pond and at 3 m below the surface of an ocean. Even though there is more water in the ocean than in the pond, the pressure on the swimmer in the pond would be the same as the pressure on the swimmer in the ocean.
The atmosphere stretches about 150 km above Earth’s surface. However, about 80% of the atmosphere’s gases are found within 10 km of Earth’s surface. At the top of the atmosphere, pressure is almost nonexistent. The pressure is close to 0 Pa because the gas particles are far apart and rarely collide. Mount Everest in south-central Asia is the highest point on Earth. At the top of Mount Everest, atmospheric pressure is about 33,000 Pa, or 33 kilo-pascals (33 kPa). (Remember that the prefix kilo- means 1,000. So, 1 kPa is equal to 1,000 Pa.) At sea level, atmospheric pressure is about 101 kPa.
Atmospheric Pressure and Depth
Take a look at Figure 3. Notice how atmospheric pressure changes as you travel through the atmosphere. The further down through the atmosphere you go, the greater the pressure is. In other words, the pressure increases as the atmosphere gets “deeper.” An important point to remember about fluids is that pressure varies depending on depth. At lower levels of the atmosphere, there is more fluid above that is being pulled by Earth’s gravitational force. So, there is more pressure at lower levels of the atmosphere.Water Pressure and Depth
Like atmospheric pressure, water pressure depends on depth. Water pressure does not depend on the total amount of fluid present. A swimmer would feel the same pressure swimming at 3 m below the surface of a small pond and at 3 m below the surface of an ocean. Even though there is more water in the ocean than in the pond, the pressure on the swimmer in the pond would be the same as the pressure on the swimmer in the ocean.
Water Pressure
Water is a fluid. So, it exerts pressure like the atmosphere does. Water pressure also increases as depth increases, as shown in Figure 4. The deeper a diver goes in the water, the greater the pressure is. The pressure increases because more water above the diver is being pulled by Earth’s gravitational force. In addition, the atmosphere presses down on the water, so the total pressure on the diver includes water pressure and atmospheric pressure.
Figure 4 Differences in Water Pressure
Water is a fluid. So, it exerts pressure like the atmosphere does. Water pressure also increases as depth increases, as shown in Figure 4. The deeper a diver goes in the water, the greater the pressure is. The pressure increases because more water above the diver is being pulled by Earth’s gravitational force. In addition, the atmosphere presses down on the water, so the total pressure on the diver includes water pressure and atmospheric pressure.
Figure 4 Differences in Water Pressure
BUOYANT FORCE
Buoyant Force and Fluid Pressure
Look at Figure 1. Water exerts fluid pressure on all sides of an object. The pressure exerted horizontally on one side of the object is equal to the pressure exerted on the opposite side. These equal pressures cancel one another. So, the only fluid pressures affecting the net force on the object are at the top and at the bottom. Pressure increases as depth increases. So, the pressure at the bottom of the object is greater than the pressure at the top. The water exerts a net upward force on the object. This upward force is buoyant force.
Look at Figure 1. Water exerts fluid pressure on all sides of an object. The pressure exerted horizontally on one side of the object is equal to the pressure exerted on the opposite side. These equal pressures cancel one another. So, the only fluid pressures affecting the net force on the object are at the top and at the bottom. Pressure increases as depth increases. So, the pressure at the bottom of the object is greater than the pressure at the top. The water exerts a net upward force on the object. This upward force is buoyant force.
Floating, Sinking, and Density
Think again about the rock in the lake. The rock displaces 5 L of water. But volumes of solids are measured in cubic centimeters (cm3). Because 1 mL is equal to 1 cm3, the volume of the rock is 5,000 cm3. But 5,000 cm3 of rock weighs more than an equal volume of water. So, the rock sinks.
Because mass is proportional to weight, you can say that the rock has more mass per volume than water has. Mass per unit volume is density. The rock sinks because it is more dense than water is. The duck floats because it is less dense than water is. The density of the fish is equal to the density of the water.
More Dense Than Air
Why does an ice cube float on water but not in air? An ice cube floats on water because it is less dense than water. But most substances are more dense than air. So, there are few substances that float in air. The ice cube is more dense than air, so the ice cube doesn’t float in air.
Less Dense Than Air
One substance that is less dense than air is helium, a gas. In fact, helium has one-seventh the density of air under normal conditions. A given volume of helium displaces an equal volume of air that is much heavier than itself. So, helium floats in air.
Think again about the rock in the lake. The rock displaces 5 L of water. But volumes of solids are measured in cubic centimeters (cm3). Because 1 mL is equal to 1 cm3, the volume of the rock is 5,000 cm3. But 5,000 cm3 of rock weighs more than an equal volume of water. So, the rock sinks.
Because mass is proportional to weight, you can say that the rock has more mass per volume than water has. Mass per unit volume is density. The rock sinks because it is more dense than water is. The duck floats because it is less dense than water is. The density of the fish is equal to the density of the water.
More Dense Than Air
Why does an ice cube float on water but not in air? An ice cube floats on water because it is less dense than water. But most substances are more dense than air. So, there are few substances that float in air. The ice cube is more dense than air, so the ice cube doesn’t float in air.
Less Dense Than Air
One substance that is less dense than air is helium, a gas. In fact, helium has one-seventh the density of air under normal conditions. A given volume of helium displaces an equal volume of air that is much heavier than itself. So, helium floats in air.
•A fluid is any material that flows and takes the shape of its container.
•Pressure is force exerted on a given area.
•Moving particles of matter create pressure by colliding with one another and with the walls of their container.
•The pressure caused by the weight of the atmosphere is called atmospheric pressure.
•Fluid pressure increases as depth increases.
•As depth increases, water pressure increases faster than atmospheric pressure does because water is denser than air.
•Fluids flow from areas of high pressure to areas of low pressure.
•All fluids exert an upward force called buoyant force.
•Buoyant force is caused by differences in fluid pressure.
•Archimedes’ principle states that the buoyant force on an object is equal to the weight of the fluid displaced by the object.
•Any object that is more dense than the surrounding fluid will sink. An object that is less dense than the surrounding fluid will float.
•The overall density of an object can be changed by changing the object’s shape, mass, or volume.
GAMES: http://www.flasharcadegamessite.com/buoyant-force-online-game.html
VIDEOS: www.youtube.com/watch?v=2fCVMhCOGWE
SOPA DE LETRAS Y JUEGAS PARA PENSAR: http://naturalezaenconstruccion.blogspot.com/
REFERENCES : http://my.hrw.com/tabnav/controller.jsp?isbn=0030462495
SCIENCE CLASS AND NOTEBOOK
VIDEOS: www.youtube.com/watch?v=2fCVMhCOGWE
SOPA DE LETRAS Y JUEGAS PARA PENSAR: http://naturalezaenconstruccion.blogspot.com/
REFERENCES : http://my.hrw.com/tabnav/controller.jsp?isbn=0030462495
SCIENCE CLASS AND NOTEBOOK