Energy’s Role

• Energy is the capacity to do work.
• Sources of energy can include:
• electricity, candles, and batteries
• the food you eat
• chemical reactions that release heat
• According to the kinetic theory, all matter is made of particles that are constantly in motion.
• Because the particles are in motion, they have
  kinetic energy, or energy of motion.
• Thermal energy is the total kinetic energy of a substance.
• The more kinetic energy the particles in the object have, the more thermal energy the object has.
• Temperature is a measure of average kinetic energy.
• Unlike total kinetic energy, temperature does not depend on how much of the substance you have.
• For example, a teapot contains more tea than a mug does, but the temperature, or average kinetic energy of the particles in the tea, is the same in both containers.
• A change of state—the conversion of a substance from one physical form to another—is a
  physical change.
• The identity of a substance does not change during
  a change of state, but the energy of a substance does change.
• A transfer of energy known as heat causes the temperature of a substance to change, which can lead to a change of state.
• A change of state—the conversion of a substance from one physical form to another—is a
  physical change.
• The identity of a substance does not change during
  a change of state, but the energy of a substance does change.
• A transfer of energy known as heat causes the temperature of a substance to change, which can lead to a change of state.
• Some changes of state require energy.
• Evaporation is the change of a substance from a liquid to a gas. Energy is needed to separate the particles of a liquid to form a gas.
• Sublimation is the process by which a solid turns directly to a gas. Sometimes ice sublimes to form a gas.
• Energy is released in some changes of state.
• Condensation is the change of a substance from a gas to a liquid. Energy is released from the gas and the particles slow down.
• Energy is also released during freezing, which is the change of state from a liquid to a solid.
• When a substance loses or gains energy, either
  its temperature changes or its state changes, but
  not both.
• Energy is released in some changes of state.
• Condensation is the change of a substance from a gas to a liquid. Energy is released from the gas and the particles slow down.
• Energy is also released during freezing, which is the change of state from a liquid to a solid.
• When a substance loses or gains energy, either
  its temperature changes or its state changes, but
  not both.

Conservation of Mass and Energy

• The law of conservation of mass says that mass cannot be created or destroyed.
• For instance, when you burn a match, the total mass of the reactants (the match and oxygen) is the same as the total mass of the products (the ash, smoke, and gases).
• The law of conservation of energy states that
  energy cannot be created or destroyed.

For instance, when you drive a car, gasoline releases its stored energy, in the form of heat, used to move the car.

Fluids

• A fluid is a nonsolid state of matter in which the atoms or molecules are free to move past each other, as in a gas or liquid.
• Fluids are able to flow because their particles can move past each other easily.

The properties of fluids allow huge ships to float, divers to explore the ocean depths, and jumbo jets
to soar across the skies.

• Buoyant force is the upward force exerted on an object immersed in or floating on a fluid.
• Buoyancy explains why objects float.
• All fluids exert pressure: the amount of force exerted per unit area of a surface.
• Archimedes’ principle states that the buoyant force on an object in a fluid is an upward force equal to the weight of the volume of fluid that the object displaces.
• The volume of fluid displaced by an object placed in a fluid will be equal to the volume of the part of the object submerged.
• An object will float or sink based on its density.
• If an object is less dense than the fluid in which it is placed, it will float.
• If an object is more dense than the fluid in which it is placed, it will sink.
• Fluids exert pressure evenly in all directions.
• For example, when you pump up a bicycle tire, air particles are constantly pushing against each other and against the walls of the tire.
• Pressure can be calculated by dividing force by the area over which the force is exerted:

Pressure = force/area

• The SI unit for pressure is the pascal (abbreviation: Pa), equal to the force of one newton exerted over an area of one square meter (1 N/m 2).
• Pascal’s principle states that a fluid in equilibrium contained in a vessel exerts a pressure of equal intensity in all directions.
• Mathematically, Pascal’s principle is stated as
  p 1 = p 2, or pressure 1 = pressure 2.
• Hydraulic devices are based on Pascal’s principle.
• Hydraulic devices can multiply forces. Because the pressure is the same on both sides of the enclosed fluid, a small force on the smaller area (at left) produces a much larger force on the larger area (at right).

EXAMPLE

Pascal’s Principle A hydraulic lift, makes use of Pascal’s principle, to lift a 19,000 N car. If the area of the small piston (A 1) equals 10.5 cm 2 and the area of the large piston (A 2) equals 400 cm 2, what force needs to be exerted on the small piston to lift the car?

. List the given and unknown values.
Given: F 2 = 19,000 N
A 1 = 10.5 cm 2
A 2 = 400 cm 2
Unknown: F 1

Write the equation for Pascal’s principle.
According to Pascal’s principle, p 1 = p 2. F 1/A 1 =F 2/A 2 = F 1 = (F 2)(A 1)/A 2

Insert the known values into the equation,
and solve F1 -= (19,000 N)(10.5 CM2)/400 CM 2 = 500 N

• Viscosity is the resistance of a gas or liquid to flow.
• Bernoulli’s principle states that as the speed of a moving fluid increases, the pressure of the moving fluid decreases.