Physics 11: Mechanical Waves + Sounds

What’s periodic motion

Hint: EQUAL INTERVALS

Motion repeated in equal intervals of time

Eg. vibrating guitar string, bobble head, swing, bouncing ball

What’s vibration

Wiggling/shaking, back+ forth motion

What’s damping

Tendency of vibrating object to lose/fade out/dissipate energy over time

Eg. hit tune fork+ slowly fades

What’s A

Amplitude of disturbance/max distance from equilibrium position (m)

What’s equilibrium

Usually drawn w dotted lines

Resting position, all forces balanced here

What’s node

Hint: Points in a standing wave where the amplitude is always zero

Min disturbance/no movement

Think: Wave on string where nodes (certain points) don't move at all while rest of the string vibrates

What’s antinode

Hint: Antinodes are At the maximum

Max disturbance, highest distance of disturbance

• In vibrating string, points that move the most (up and down the most) = antinodes

What’s T

Period (s)

Time to complete FULL cycle of one wave to pass

• Eg. time for waves hitting feet, how long btwn wave hits

Full cycle: full motion completed btwn one point to next (eg. crest→crest)

What’s resonance

When forces applied to vibrating/oscillating object @ time interval = to period of oscillation→ amplitude increases

Eg. push friend on swing, correct timing to maintain pendulum clocks accurate (so don’t lose their energy during woo woo swings)

What’s all these variables in the formula

T=period (s) (time for full cycle)

l=length of massless rod/string (m)

g= gravitational field strength (N/kg or m/s²)

*Mass and amplitude are irrelevant→ not in formula

For this pendulum, to complete a full cycle and be ready to repeat it has to..?

Swing from right→left→back to right

If you put any mass on a spring vertically→it’ll ____????

Oscillate/bound up+down

On d-t graph: looks like since curve

What’s a wave

Disturbance (basically make string go wee weooo) that carries energy thru matter/space

What are mechanical waves

Waves that need physical medium (stuff, matter) to travel thru

Eg. water waves, sound waves, waves along a rope

What’s a medium

Any physical matter like air, water, rope, etc

What’s transverse waves

Think: spider man goes up and down

Waves that displace medium w pulse disturbance that’s perpendicular to direction of wave itself (basically has amplitude)

What’s longitudinal waves

Waves that displace medium w pulse disturbance that’s parallELLLL to direction of wave itself (basically front n back)

What’s surface waves

Made up of both longitudinal + transverse waves → circular waves

What’s A

Amplitude (m)

Max distance from equilibrium

Energy displayed in the amplitude of the wave… more energy= larger amplitude

What’s ^{𝛌 (lambda)}

Wave length (m) length of one COMPLETE wave

Basically crest→crest / trough→trough

THINK: length to complete a wwwaavveee (italize)

What’s v

Speed (m/s)

How fast wave travels

Depends on MEDIUM it travels thru, (density, thickness, stiffness etc)

PS. More energy CANT make wave travel faster→only makes bigger amplitude

• Think: v=d/t, doesn’t care abt frequency, just abt cycles finished

What’s in phase and out of phase

In phase: Crests match

Out of phase: crests DONT match

What’s cursive f

Frequency

Hz OR cycles/s

How many waves pass/second

If wave’s travelling thru one medium→speed is constant

To change velocity of wave, must change MEDIUMS

Think: d/t doesn’t have anything abt frequency, no matter frequency its still same d and t

When incident wave hits fixed boundary,

It’ll be reflected→Opposite vertical (inverted)

Waves travel at speeds according to medium it’s in

If medium changes→speed+other behaviour of waves change

What’s reflection

Throwing back of body/light/, heat, sound w out absorbing it

If energy continues into new medium, some→reflected… In two these situation: new medium 1. more dense/2. less dense?

1. If new medium MORE dense, some energy goes onward into this new medium. The reflection is INVERTED

   1. THINK: if the NEW person is more dense→ some energy goes onward into this new medium (we know) + reflection is INVERTED bc they have an INVERTED view on the world
      

2. If new medium=LESS dense, some energy goes onward into this new medium. The reflection is UPRIGHT

   1. THINK: New person (medium) is less dense→ some energy goes onward into this new medium (we know) + reflection is upRIGHT

T or F:.. When frequency of wave is altered by crossing boundary

False pookie :(

When frequency of wave is NOT ALTERED by crossing boundary

But v might change if change in energy source

T or F: reflected pulse becomes INVERTED when wave less dense rope is heading toward boundary w more dense rope

YES!!!

Reflected pulse becomes INVERTED when wave less dense rope is heading toward boundary w more dense rope

T or F: Amplitude of incident pulse=always NEVER GREATER than amplitude of reflected pulsve

FALSE.

Amplitude of incident pulse=ALWAYS. GREATER than amplitude of reflected pulse

BC transfer of some energy into wall

What’s superposition

Displacement of medium caused by 2/+ waves = sum of displacement by individual waves (interference)

→Constructive OR destructive interference

What’s standing waves

Combo of 2 waves moving in opp directions, each having same amplitude +frequency

This cool thing is result of interference (when waves r superimposed), energies either added together (antinodes) or cancel out (nodes)

What’s the law of reflection

NORMAL LINE= dotted line=perpendicular direction from surface. Ref point for angle of incidence+ angle of reflection

^𝛳i =angle of incidence

^𝛳r=angle of reflection

→Direction of reflected wave w ref to normal (not surface of barrier)

→reflection is still in same medium so .. same velocity, Hz, wavelength, but NEW DIRECTION POOKEH!!

How would echo from insect flying TOWARD BAT differ from insect flying away from bat???

Think: car nyoom

Insect flying to bat: higher Hz from bat

Flying away from bat: lower Hz from bat

What’s the law of refraction

Bending of path of light wave that passes from one material to another

Occurs at boundary

Caused by change in speed of light wave upon crossing of boundary

Hz doesn’t change as usual