Physics 2 - Exam 1 - Ch 16-21

diff btw oscillation & waves (ch 16)

(ch 16) In a simple harmonic oscillator, if an object is displaced from equilibrium and set in motion, at which point is velocity the greatest?

Equilibrium point (X = 0)

?? On a general frictionless surface, which direction indicates a frictionless surface? Which direction indicates the presence of friction?

-X = frictionless

+X = friction

What is the restoring force on a pendulum on Earth?

gravity

T/F? Oscillation can create waves, in real time.

True

Total Energy =

KE + PE

• PE can be static or elastic

What would the graphs of Total Energy (TE), KE, & PE look like when graphed on an energy vs. time graph for an object oscillating on a spring?

• TE would be a flat horizontal line at the highest value (relative to KE & PE)

  • constant

• KE and PE would be alternate sine waves, whose peaks are at TE & troughs are at 0

  • peaks and troughs don’t align

crest

peak of a wave

trough

lowest point of a wave

A single note of a banjo starts out loud and slowly quiets over time. What happens to the sound waves in terms of period (T), f and amplitude (X) as the sound decreases in volume?

• Amplitude decreases

• T & f stay about the same

A babysitter is pushing a child on a swing. At the point where the swing reaches 𝑋, where would the corresponding point on a wave of this motion be located?

𝑋 is the maximum deformation, which corresponds to the amplitude of the wave. The point on the wave would either be at the very top or the very bottom of the curve.

Know this (circuit info)

T is ___ counter, while f is ____ counter.

time; wave

longitudinal wave

disturbance (X) is parallel to direction of propagation (v)

what kind of wave is sound?

longitudinal

transverse wave

(typical thing when u think of wave)

constructive v. destructive interference

c = amplitudes add together

• while the wavelength (and frequency) of the resulting wave remains the same

d = amplitudes subtract from each other

nodes vs antinodes

• NOdes are areas of wave interference where there is NO motion. (connection between loops)

• Antinodes are areas of wave interference where the motion is at its maximum point. (bumps)

Imagine you are holding one end of a jump rope, and your friend holds the other. If your friend holds her end still, you can move your end up and down, creating a transverse wave. If your friend then begins to move her end up and down, generating a wave in the opposite direction, what resultant wave forms would you expect to see in the jump rope?

The rope would alternate between having waves with amplitudes two times the original amplitude and reaching equilibrium with no amplitude at all. The wavelengths will result in both constructive and destructive interference

Which measurement of a wave is most important when determining the wave's intensity?

Amplitude, because a wave’s energy is directly proportional to its amplitude squared.

constructive interference

when two waves arrive at the same point exactly in phase; that is, the crests of the two waves are precisely aligned, as are the troughs

destructive interference

when two identical waves arrive at the same point exactly out of phase; that is, precisely aligned crest to trough

rarefaction v. compression of sound waves

audible hearing range (frequency)

20 - 20,000 Hz

review pre-quiz questions

Imagine you observe two fireworks explode. You hear the explosion of one as soon as you see it. However, you see the other firework for several milliseconds before you hear the explosion. Explain why this is so.

Sound and light both travel at definite speeds. The speed of sound is slower than the speed of light. The first firework is probably very close by, so the speed difference is not noticeable. The second firework is farther away, so the light arrives at your eyes noticeably sooner than the sound wave arrives at your ears.

You observe two musical instruments that you cannot identify. One plays high-pitch sounds and the other plays low-pitch sounds. How could you determine which is which without hearing either of them play?

Compare their sizes. High-pitch instruments are generally smaller (eg. flute)

than low-pitch instruments (eg. tuba) because they generate a smaller wavelength.

loudness

experience of amplitude

• as amplitude increases, perceived loudness increases

sonic boom

constructive interference of sound created by an object moving faster than sound

• bow wake created

why can’t people inside plane hear the boom?

inside the “cone,” sound waves are mostly destructive —> decreased intensity heard inside the plane

There is no change in frequency when source and observer move together because it fits your experience.

std vs. noise-canceling headphones

Regular headphones only block sound waves with a physical barrier.

Noise-canceling headphones use destructive interference to reduce the loudness of outside sounds.

How is it possible to use a standing wave's node and antinode to determine the length of a closed-end tube?

When the tube resonates at its natural frequency, the wave's node is located at the closed end of the tube, and the antinode is located at the open end. The length of the tube is equal to one-fourth of the wavelength of this wave. Thus, if we know the wavelength of the wave, we can determine the length of the tube.

pitch

perception of frequency

Why is it possible to use ultrasound both to observe a fetus in the womb and also to destroy cancerous tumors in the body?

diff intensities (higher destroys tumors)

17.8!! worked example

polarization of neutral objects.

sep of charges while object still remains neutral

gravitational force is completely negligible on a SMALL scale, where the interactions of individual charged particles are important (F_elec)

Gravitational force on a large scale dominates interactions between large objects because it is always attractive, while Coulomb forces tend to cancel.

G Force

6.67E-11

18.3 eg meaning?

elec filed is stronger between which types of charges? why?

unlike charges

• fields from each charge point in same direction —> their strengths add

• meaning??

  • “field of two unlike charges is weecause the fields of the individual charges are in opposite directions and so their strengths subtract. At very large distances, the field of two unlike charges looks like that of a smaller single charge.”

on parallel plates, The force on the charge is the same no matter where the charge is located between the plates. This is because the electric field is uniform between the plates.

dielectric strength

maximum electric field strength above which an insulating material begins to break down and conduct

E & I travel in the ___ direction. Why?

same;

bc E = -V/q (?)

—> which means it follows the direction of decreasing potential (which is how Current travels)