Chapter 1.2 Notes Pressure

All matter is made up of atoms and molecules. All matter is made up of atoms and molecules. Matter can exist in four states: Matter can exist in four states: Liquid, Solid, Gas, and Plasma

In a Solid, molecules are constantly moving, but they do no move around in the solid but instead vibrate in a fixed location.

In a Liquid, molecules are no longer confined to a fixed position. Molecules vibrate, but can now easily slide over one another and move about – it takes the shape of its Container.

In a Gas, molecules move freely about the container. When they hit each other or the container they bounce around like billiard balls. The shape of a gas takes the shape of the container.

In temperatures above 2000 degrees Celsius, electrons separate from atoms to form ions. A gas containing free electrons and ions is called Plasma.

Both liquids and gases are fluids. A fluid is a material that can flow, has no definite shape of its own, and conforms to the shape of its container. fluids

A hydraulic system uses a liquid as a fluid, which is called a working fluid. A hydraulic system uses a liquid as a fluid, which is called a working fluid.

Hydraulic Robot Demo

A pneumatic system uses a gas as its working fluid. A pneumatic system uses a gas as its working fluid.

The density of a material is the amount of matter per unit volume. The density of a material is the amount of matter per unit volume.density Density = mass / volume Density = mass / volume SI Units of density is kg/m 3 SI Units of density is kg/m 3

Coke versus Diet Coke

Density is sometimes written as a comparison of an object’s weight to its volume. This is called weight density. Density is sometimes written as a comparison of an object’s weight to its volume. This is called weight density. Weight density = Weight density = weight / volume SI units of weight density are N/m 3 SI units of weight density are N/m 3

A volume of 500 cm3 of a fluid has a mass of 550 g. What is the density? Density = mass/volume Density = mass/volume Density = 550kg / 500cm 3 Density = 550kg / 500cm 3 Density = 1.1 kg/cm 3 Density = 1.1 kg/cm 3

A force applied over a surface is pressure. A force applied over a surface is pressure.pressure Pressure = Pressure = force / area SI units of pressure are N/m 2 or Pascal SI units of pressure are N/m 2 or Pascal

Pressure Demos Bed of Nails Bed of Nails Bottomless Bottle Bottomless Bottle

A block has an area of.01 m 2 and exerts a force of 50 N on a table. Calculate the pressure the block exerts. Pressure = Force / Area Pressure = Force / Area Pressure = 50 N /.01 m 2 Pressure = 50 N /.01 m 2 Pressure = 5000 Nm 2 or Pascals Pressure = 5000 Nm 2 or Pascals

The pressure increases as the depth increases. The pressure increases as the depth increases.pressure Pressure = weight density x fluid depth Pressure = weight density x fluid depth

The height of a fluid in a storage tank is 100 cm above a valve. Find the pressure at the valve if the weight density is 13.6 g / cm Pressure = weight density x depth 2. Pressure = 13.6 g/cm 3 x 100 cm 3. Pressure = 1360 g/cm 2

Water exerts an upward force on all objects. This upward force is called the buoyant force and is caused by the pressure increasing with depth.

Page 35, draw in figure 1.20

If buoyant = weight density x Volume = weight of water displaced If buoyant = weight density x Volume = weight of water displaced If the weight of the brick is greater than the buoyant force, the brick will sink. If the weight of the brick is greater than the buoyant force, the brick will sink. If the weight of the brick is less than the buoyant force, the brick will float. If the weight of the brick is less than the buoyant force, the brick will float. If the weight of the brick is equal to the buoyant force, the brick will stay in the same place. If the weight of the brick is equal to the buoyant force, the brick will stay in the same place.

Archimede’s Principle Archimede’s Principle states that an object immersed in a fluid has an upward force exerted on it equal to the weight of the fluid displaced by the object. Archimede’s Principle

Two simple density rules of whether an object will float: 1. If the object has a greater density than the fluid, it will Sink. 2. If the object has a lower density than the fluid, it will Float.

Use table 1.4 on page 30 to answer this question: Use table 1.4 on page 30 to answer this question: Will a block of lead float or sink in mercury? Will a block of lead float or sink in mercury? Lead has a density of 11.3 and Mercury Float Lead has a density of 11.3 and Mercury Float

Pascal’s Principle says a change in pressure at any point in a confined fluid is transmitted undiminished throughout the fluid. Pascal’s Principle says a change in pressure at any point in a confined fluid is transmitted undiminished throughout the fluid. Pascal’s Principle Pascal’s Principle

P1 = P2; Since pressure = F/A; F1/A1 = F2/A2 P1 = P2; Since pressure = F/A; F1/A1 = F2/A2 Suppose F1 = 10N, what is the F2 if A1=.1 m 2 and A2 = 2 m 2 ? Suppose F1 = 10N, what is the F2 if A1=.1 m 2 and A2 = 2 m 2 ? F1/A1 = F2/A2 F1/A1 = F2/A2 10/.1 = F2 / 2 10/.1 = F2 / = F2 / = F2 / 2 2 x 100 = F2 2 x 100 = F2 200 N = F2 200 N = F2

On earth, we live at the bottom of a thick blanket of air. On earth, we live at the bottom of a thick blanket of air. Air also has pressure. Air also has pressure. Air pressure is caused by the weight of air above an area. Air pressure is caused by the weight of air above an area. Air pressure Air pressure Atmospheric pressure decreases with altitude. Atmospheric pressure decreases with altitude. A barometer is an instrument used for measuring atmospheric pressure. A barometer is an instrument used for measuring atmospheric pressure.

Atmospheric Pressure Demo Equilibrium Equilibrium

At sea level, the average atmospheric pressure is This equals a height of 760 mm of mercury, and this pressure is called one atmosphere. At sea level, the average atmospheric pressure is This equals a height of 760 mm of mercury, and this pressure is called one atmosphere. Absolute Pressure is the total pressure measured above zero pressure (a perfect vacuum). Absolute Pressure is the total pressure measured above zero pressure (a perfect vacuum). Gage Pressure is the pressure measured above atmospheric pressure. Gage pressure is a measure of how much greater the air pressure is inside the tire than the air pressure outside the tire. Gage Pressure is the pressure measured above atmospheric pressure. Gage pressure is a measure of how much greater the air pressure is inside the tire than the air pressure outside the tire. Absolute pressure = gage pressure + atmospheric pressure Absolute pressure = gage pressure + atmospheric pressure

The gage pressure is 33 psi and the atmospheric pressure is 14.7 psi, how much is the absolute pressure? The gage pressure is 33 psi and the atmospheric pressure is 14.7 psi, how much is the absolute pressure? Absolute pressure = gage + atmospheric Absolute pressure = gage + atmospheric Absolute = Absolute = Absolute = 47.7 Absolute = 47.7

Fluid systems have 2 things in common. First they both contain a fluid. Second, they have a pressure difference in the system that creates a force. Pressure is a prime mover in fluid systems. Fluid systems have 2 things in common. First they both contain a fluid. Second, they have a pressure difference in the system that creates a force. Pressure is a prime mover in fluid systems. If there is no pressure difference in a system, there is no movement. If there is no pressure difference in a system, there is no movement. If a pressure difference exists, the fluid will flow until it creates equilibrium. If a pressure difference exists, the fluid will flow until it creates equilibrium. In equilibrium, h2 must equal h1 and P2 must equal P1. In equilibrium, h2 must equal h1 and P2 must equal P1.