Warm-Up: What do you think of when you hear the word “waves”?

Warm-Up: • What do you think of when you hear the word “waves”? • What do you think it means for something to oscillate?

Lesson 2.1 – Oscillating Motion • Objectives: • I can explain what oscillatory motion is, and give examples. • I can define what it means for a motion to be periodic • I can determine the direction of the force in oscillatory motion, and identify the equilibrium position of the object.

Oscillatory Motion: • Oscillatory motion is defined as ________________________ motion, around an _________________ point. • Oscillatory motion is __________________, which means that it repeats itself. back-and forth equilibrium periodic

Equilibrium point. The pendulum swings left and right, but always passes through this point in space. • The force in any oscillatory motion is always in an opposite direction from the displacement of the moving object from the equilibrium point. • This is what causes the object to return toward the equilibrium point.

Examples of Oscillatory Motion: Pendulums (like those in a clock!) Musical metronomes Swings on a playground Speakers blasting music

Quick Check: • See if you can answer the questions on your half-sheet! • Work by yourself first, to make sure you understand before we move on!

#1. Oscillatory motion is best defined as… • A. Left and right motion repeated. • B. Up and down motion repeated. • C. Un-ending circular motion • D. Any motion that repeats itself, back- and forth in opposite directions.

#2. In your own words, what does it mean for motion to be periodic?

#2. In your own words, what does it mean for motion to be periodic? • Any motion that is periodic repeats itself over time.

#3. Use the diagram below. • Which point represents the equilibrium position • Which direction is the force acting on the child at point X? • Which direction is the force acting at point Z?

#3. Use the diagram below. • Which point represents the equilibrium position • Which direction is the force acting on the child at point X? • Which direction is the force acting at point Z? Equilibrium

Lesson 2.2 – The Anatomy of a Wave • Objectives: • I can identify the crest, wavelength, and amplitude of a wave. • I can define the frequency of a wave and recognize its units.

What do you think of when you hear “waves”? • Most of us think about waves in the ocean. • But in reality, waves are all around us!

Definition of a Wave: • In physics, waves are ___________________ disturbances that travel through space and time. • Remember what it means for an object to oscillate from 10 minutes ago? oscillatory

Examples of things that travel in waves: • Visible light • Sounds • Vibrations from earthquakes • Energy (electromagnetic radiation)

Parts of a Wave: Wavelength Crest Equilibrium Amplitude time

Think of waves as a never ending “roller coaster” for particles or energy. • The amplitude is the height of the hills. • The wavelength is how far apart the hills are. • But how do we know how fast the particles are moving in a wave??

#1. Count how many cars pass by in 15 seconds

#2 Count how many cars pass by in 15 seconds

Calculate the frequency (in cars/sec) for each observation: • ___________________ • ___________________ • ___________________ • ___________________

Defining Frequency: • Frequency can be a difficult property to grasp at first, but soon becomes intuitive!  • It is not a physical characteristic, but rather a measured speed. • We define frequency as: ________________________________________________________________________________. the number of wavelengths that pass a point per second.

Frequency has units of ___________. We can also call this a _______________. • The Frequency-Wavelength Trade-Off: • In general, the higher (faster) the frequency of a wave, the ________________ its wavelength. 1/seconds Hertz (Hz) shorter

Example: Which wave would you expect to have a lower frequency? WHY? A B

Lesson 2.3 – Types of Waves • Objectives: • I can differentiate between transverse and longitudinal waves, and give examples of each type of wave. • I can describe transverse and longitudinal waves in terms of the direction of their motion, relative to the direction of their oscillation.

Longitudinal Waves – also called compression waves. • The motion of the wave oscillation is in the SAME direction that the wave travels.

Transverse Waves – direction of the wave oscillation is in the perpendicular direction to it’s motion.

Lesson 2.4 – Sounds • Objectives: • I can explain how sound travels in waves. • I can identify the relationship between pitch and frequency. • I can explain the Doppler Effect in terms of frequency of sound waves.

Sound waves are mechanical waves. This means that they rely on a medium to carry them. • Medium = any substance a wave must travel through • Air • Glass • Water • Insulation • Drywall

MECHANICAL WAVES CANNOT TRAVEL IN A VACUUM (SPACE) • They rely on the molecules in the medium to carry them through vibrations.

The sounds we hear are measured in Hertz (Hz). • This means how many vibrations happen per second. (1/s) • A “middle C” in music = ~256 Hz or 256 vibrations per second.

What kind of wave is sound?? • Longitudinal (Compression)

Compressions and Rarefactions

A sound wave is a pressure wave; regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. These compressions and rarefactions result because sound • is more dense than air and thus has more inertia, causing the bunching up of sound. • waves have a speed that is dependent only upon the properties of the medium. • is like all waves; it is able to bend into the regions of space behind obstacles. • is able to reflect off fixed ends and interfere with incident waves • vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations.

When sound is played at various frequencies, we can detect the frequency with our ears! • In music, we call this the pitch of the sound. • Higher frequency waves = higher pitch

Humans can hear a wide range of frequencies: • 20 Hz – 20,000 Hz • Some animals can hear different ranges • Dogs can hear up to 45,000 Hz • Cats can hear up to 85,000 Hz

The intensity of a sound is how much energy it carries in its wave. • We can measure the “loudness” of a sound relative to its intensity using decibels (dB) • Higher dB = louder sounds!

An automatic focus camera is able to focus on objects by use of an ultrasonic sound wave. The camera sends out sound waves that reflect off distant objects and return to the camera. A sensor detects the time it takes for the waves to return and then determines the distance an object is from the camera. • If a sound wave (speed = 340 m/s) returns to the camera 0.150 seconds after leaving the camera, how far away is the object?

On a hot summer day, a pesky little mosquito produced its warning sound near your ear. The sound is produced by the beating of its wings at a rate of about 600 wing beats per second. • What is the frequency in Hertz of the sound wave? • Assuming the sound wave moves with a velocity of 350 m/s, what is the wavelength of the wave?

Interference:

The Doppler Effect – a moving sound sources compresses sound waves so that the observer hears a higher frequency (pitch) as the sound source approaches and a lower frequency as the sound source fades away.

Sound waves can… • Reflect (echo) • Defract (travel around corners/obstacles) • Refract (bend their path)

Reflection: an incoming sound wave/light ray strikes a surface and is not absorbed, by rather reflected back into a different direction.

Defraction: the wave changes direction and “bends” around obstacles or through gaps.

Refraction: the waves bend as they cross between two different mediums (think light/water)

Warm-Up: What do you think of when you hear the word “waves”?