Final Exam Review
Physics 115
December 14, 1998
I am hoping to come up with about 50 questions. I have not decided whether they will be all multiple choice.
Electricity
Go over hour exam.
Go over Experiment E6.6
Make sure you go over the handouts on Electrostatics
and Magnetism.
There will be more questions like the ones on the hour exam.
Know about conductors and insulators.
Know which materials are magnetic.
Know all the components and their units of electricity:
Charge, current, resistance, potential difference, electrical energy, electrical power, electrical force, capacitance, inductance (didn't cover, will not ask about), magnetic poles, magnetic force.
We have dealt with direct current (DC). Almost all power sources produce alternating current voltage and current (AC).
This is because it is much easier to produce AC voltage using electromagnetic means. AC voltage moves positive and negative.
We use devices to change voltage from AC to DC when we need it.
Magnetic fields originate from moving charges.
Only moving charges feel a force in a magnetic field, not stationary charges. F=qvB, where B = magnetic field.
There is no force if the velocity is along the same direction as the magnetic field.
All of electricity and magnetism (called electromagnetism) can be understood by Maxwell's four equations.
These equations also prove that light basically consists of electric and magnetic field.
Light is part of electromagnetism.
Motion, Force, and Gravity
Speed describes how fast a body moves:
Instantaneous speed describes the speed at any instant.
Average speed describes the speed over some time period.
On a graph of distance versus time, we have found that the speed is the slope.
In order to describe speed and direction, we have to be sure of our frame of reference. We describe position, velocity, etc. in a reference frame. Remember the train shooting the ball up.
Scalar: a scalar quantity describes magnitude only.
Vector: a vector quantity describes both direction and magnitude.
Describe where I am with respect to you. It doesn't suffice to say 3 m. That would be on a circle of radius 3 m. You also have to give the direction. You could say 3 m south, or 3 m toward the computer. We often find vectors necessary to describe motion.
We call a description of where something is located a position vector.
Now let's define more precisely speed and velocity.
speed: only magnitude
velocity: magnitude and
direction.
Two cars moving with the same speed do not necessarily have the same velocity. One could be traveling north and the other south.
We use boldface to indicate vectors or arrows over the quantity.
acceleration is the rate of change of velocity.
note that v and a are vectors!
Acceleration can be due to a change in speed or a change in direction.
Circular motion at constant speed is called centripetal
acceleration..
Inertia is the property of a body that causes it to remain at rest or in motion unless acted upon by an outside force.
Newton's 1st Law
A body remains at rest or continues in uniform motion except when compelled to change its motion by forces acting upon it.
Also called the law of inertia.
New concept:
momentum, p
p = mv
What is a force?
A force is a push or pull. We used springs to express them.
A force is a vector.
There are four fundamental forces:
gravitational
electromagnetic
strong (nuclear)
weak (beta decay)
We must distinguish between external and internal forces.
External (or outside) forces are agents of change.
Examples of internal forces are the electromagnetic ones holding the body together, both inside the atoms and between the atoms.
Most of the forces with which we are familiar are electromagnetic.
Newton's 2nd Law
Force is defined as the rate of change of momentum.
The force and 
are vectors in the
same direction.
The instantaneous force occurs over a very small D t.
The SI unit of force is the newton.
1 N = 1 kg m/s2
If we always use SI units, then the answer will always be in SI units. If we use velocity in cm/s, the answer will not be in N.
Newton's 3rd Law.
Whenever one body exerts a force on a second body, the second body exerts a force of equal magnitude and opposite direction on the first body.
"For every action, there is a equal and opposite reaction."
Conservation of Linear Momentum.
In the absence of a net external force, the linear momentum of a body, or of a system of bodies, is always conserved.
Gravitation
We call the acceleration with which a body falls
to Earth, the acceleration of gravity and use the symbol g
to denote it. It is fairly constant over the surface of the Earth, but decreases
with altitude as we shall see.
F = ma = mg
The direction of g is towards the center of Earth.
Projectile motion is always a parabola, because there is only a vertical force. The vertical speed changes due to gravity, but the horizontal speed is constant.
Newton's Law of Universal Gravitation
There exists an attractive interaction between any
two material bodies in the universe.
Temperature is different than heat and thermal energy.
Temperature is what thermometers measure. It is an indication of the internal kinetic energy of the object.
The kelvin scale uses 0 K as the absolute zero temperature. It is related to the celsius scale by
Thermal energy is the sum of the internal potential and kinetic energies of all the atoms and molecules of a body.
We measure energy in the SI unit of joules. In more common use is calories.
cal = calories
J = joules
1 cal = 4.186 J
1 calorie is the amount of heat required to raise the temperature of 1 g of water by 1 0C.
1 Calorie = 1 kcal
Calorie is the food energy unit.
Specific heat capacity refers to the ability of a substance to store thermal energy.
Units: cal/g 0C
See table on page 300
Q = heat transfer
Q = mcD T
c = 1.0 cal/goC for water
c = 0.5 cal/goC for ice
c = 0.48 cal/goC for steam
How is energy transferred?
Conduction
Convection
Radiation
Phase Changes
As we go up the temperature scale:
Melting, evaporation (or vaporization).
As we go down the temperature scale:
Condensation, freezing (or solidification).
Some substances skip a phase: sublimation goes from solid to gas like CO2.
Latent heat of fusion is the energy required to go from solid to liquid. 80 cal/g for water.
Latent heat of vaporization is the energy required to go from liquid to gas. 540 cal/g for water.
When the phase changes goes in the opposite direction, negative values of energy occur. When water freezes, energy is released.
Evaporation is not the same as boiling. Evaporation takes place at the surface of the liquid. It takes energy to evaporate the molecules, and the object then feels cooler. That is why we sweat.
Zeroth law: Two bodies in thermal equilibrium with a 3rd body are in thermal equilibrium with each other.
First law: Energy is conserved in all transformations in an isolated system.
Second law: Within an isolated system, some (but never all) heat from a source can never be converted into work or mechanical energy.
Heat input = work output + waste heat output
Heat engines extract heat from a hot reservoir, does work, and expels part of the heat to a colder reservoir.
Max Eff = 
can never be 100%
Internal combustion car engines are examples of heat engines.
Second Law has several forms: heat flows spontaneously from a hotter body to a colder body, never the other way around.
Heat pumps require work to take heat from a cold body and remove it to a warm body. Refrigerators, freezers, and air conditioners do this.
Entropy: the entropy of an isolated system never decreases.
Matter
Space, time, matter, and energy constitute what we call the physical world.
Four fundamental properties: length, time, mass, and electric charge.
Derived quantities: speed, energy, electric current, magnetism, force
Scientific methodology-know it!
Note Eratosthenes's measurement in the 3rd century B.C. for the circumference of Earth.
Chapter 4 is the most important chapter.
Know chemical notation and chemical formulas.
Know how to balance chemical reactions.
Example: burn natural gas (mostly methane)
CH4 + 2O2 ® CO2 + 2H2O
There is no detectable change in the total mass during
a chemical reaction.
Chemical compounds (molecules) are formed when atoms of different elements join together to make identical units.
Know ionic and covalent bonding.
Understand notation for bonding.
Cohesion is the tendency for like molecules, such as those of water, to attract each other.
Surface tension, a consequence of cohesion, is the tendency of polar liquids (especially) to pull toward each other.
Adhesion is the tendency of unlike molecules to stick to each other (meniscus). (Adhesion forces between water and glass is stronger than cohesive forces of water).
Capillary action is the ability of water or other polar liquids to pull themselves through small tubes; it occurs when the bore of the tube is so small that the surface adhesion is stronger than any other force acting on the liquid.
Hydrogen bonds occur between a hydrogen atom in a polar molecule and the negatively charged portion of another polar molecule. A hydrogen atom is left with a considerable positive charge when it shares its single electron with atoms such as oxygen, fluorine and nitrogen in a polar molecule.
An acid is a compound that increases the concentration of hydrogen ions (H+) when dissolved in water.
A base is a compound that increases the concentration of hydroxide ions (OH-) when dissolved in water.
Know about pH.