PHYSICS 221Topic Checklist
UNIT 3
We finish up by studying the fields of wave motion and thermal physics.
Chapter 11 Harmonic Motion and Waves Many of the most important and interesting phenomena in nature involve repetitive motion. Sound and light waves are obvious examples.
q Simple Harmonic Motion This is a technical term for the behavior of a mass moving under the influence of a restoring force. Such a body has an equilibrium position at which this force is zero. As the body is displaced from its equilibrium position the restoring force tries to move it back. For true harmonic motion, the restoring force must be proportional to the displacement from equilibrium.
where k is called the spring constant. The result is that the mass will oscillate back and forth between two turning points. In such problems always choose the coordinate origin to be the equilibrium position.
q Amplitude The distance from the equilibrium position to the turning point.
q Elastic Potential Energy
q Total Energy
q Period The time for one complete cycle.
q Frequency The number of cycles per second.
The unit of frequency is the hertz. 1 Hz = 1 cycle per second.
q Simple Pendulum
q Damping and Resonance
q Wave Motion Crests and troughs.
q Wavelength Distance from crest to crest.
q Amplitude Maximum height of a crest. Determines the energy of the wave.
q Wave Velocity Speed at which wave propagates.
q Interference of Waves Occurs when two waves meet. Know the conditions for constructive and destructive interference.
q Types of Waves
§ Transverse: The direction of vibration is perpendicular to the direction of propagation. Waves in the strings of musical instruments are examples of this type. The speed of waves in a stretched string depends on the tension and density:
§ Longitudinal: The direction of oscillation is parallel to the direction of propagation. Sound in air is an example of longitudinal waves.
q Standing Waves
§ Nodes: Positions of no vibration due to destructive interference.
§ Antinodes: Positions of maximum vibration due to constructive interference
q Resonant Frequencies The natural frequencies at which standing waves can exist depend upon the size of the vibrating material.
Be able to sketch standing wave patterns and compute allowed wavelengths and frequencies.
Chapter 12 Sound Sound is the most obvious example of wave motion. This chapter develops some of the properties of sound waves in air.
q Speed The speed of sound in air at 0° C is 331 m/s. Add 0.6 m/s for each degree above zero.
q Pitch The pitch is determined by the frequency. The audible range for humans is about 20 Hz to 20 kHz.
q Loudness The loudness is determined by the amplitude. One measure of loudness is called intensity which is the power per unit area transported by the wave. Intensity is measured in W/m2.
q Decibels An alternative measure of loudness is the decibel. The decibel corresponds more closely to human response than does the W/m2.
where I0 is the reference level, chosen to be the threshold of hearing, 1x10-12 W/m2.
If the perceived loudness of a sound is doubled,
§ The intensity is multiplied by 10.
§ The intensity level is increased by 10 dB.
Chapter 13 Temperature This chapter begins the study of thermal physics. You will learn what effects temperature has on substances and why they occur.
q Temperature Scales Fahrenheit, Celsius, and Kelvin.
q Thermal Expansion: Linear and volume expansion.
q Ideal Gas Law The state of a gas is given by specifying its pressure, volume, and absolute temperature.
where n is the number of moles of gas and R is the universal gas constant. In MKS units R = 8.315 J/mol K. In the units used in chemistry R = 0.082 l atm/mol K.
q Avogadro’s Number NA = 6.02 x 1023 molecules/mole
q Change of State Problems If the number of moles does not change, the states 1 and 2 are related by:
q Distribution of Molecular Speeds
q Evaporation
q Vapor Pressure, Partial Pressure
q Relative Humidity
q Dew Point
Chapter 14 Heat This chapter is about heat as a form of energy.
q Internal Energy Energy of a substance due to molecular motion.
q Specific Heat Capacity The amount of heat required to raise the temperature of one gram of a substance by 1°C.
Q = mcDT
q Calorimetery Problems Heat gained equals heat lost.
q Latent Heat Heat involved in phase changes. Melting and boiling.
Q = mL
q Heat Transfer
§ Conduction: Heat moving through a substance.
§ Convection: Heat carried by motion of fluids.
§ Radiation: Energy contained in electromagnetic waves.
Chapter 15 Thermodynamics This chapter describes some of the processes by which heat energy can be harnessed to do useful work. The limits on the efficiency of such processes are shown.
q First Law of Thermodynamics Include heat in the law of conservation of energy.
DU = Q – W
q Thermodynamic Work The work done by an expanding gas.
q Efficiency is the ratio of the work output to heat input.
q Special Processes
§ Isothermal: Constant temperature
§ Isobaric: Constant pressure
§ Adiabatic: No heat flow
q Second Law of Thermodynamics Defines “allowable” processes and limits efficiency of thermal devices.
§ Heat will not flow spontaneously from a cold body to a hot one.
§ No device can change a given amount of heat completely into work.
§ Natural processes tend toward a state of greater disorder.
q Entropy A measure of the disorder in a system. In any process the total entropy of a system plus its environment must be positive.
