What are waves?

Wave Definition: A disturbance that transfers energy from place to place. What carries waves? A medium, a medium is the material through which a wave travels. A medium can be a gas, liquid, or solid.

Medium These media are distinguished by their properties - the material they are made of and the physical properties of that material such as the density, the temperature, the elasticity, etc. Such physical properties describe the material itself, not the wave.

Not all waves require a medium to travel. Mechanical Waves are waves that require a medium. Electromagnetic Waves travel through empty space and do not require a medium.

What causes waves? Waves are created when a source of energy causes a medium to vibrate. A vibration is a repeated back and forth or up and down motion.

Lab: Slinkys in Action Use a slinky to make different types of waves. Notice how the ribbon moves with each different type of wave. Where did the energy come from to start the wave? How could you tell the wave carried energy?

Types of waves: Waves are classified according to how they move.

Transverse Wave Teacher’s Domain Animation Use a marker to trace a particles motion as the wave travels through the medium. How does the particle move with respect to the direction of the wave?

Transverse wave (sometimes called a sine curve or wave) Waves that move the medium at right angles to the direction in which the waves are traveling is called a transverse wave 3:15min.transverse wave 3:15min. Transverse means across. The highest parts are called crests the lowest parts are called troughs.

Draw & Label a Transverse Wave

Compressional or Longitudinal Wave Matter vibrates in the same direction as the wave travels. Longitudinal discussionLongitudinal discussion 3:36 min

Compressional or Longitudinal wave The parts, where the coils are close together are called compressions, the parts where the coils are spread out are called rarefactions. Teacher’s Domain animation

Draw & Label a Compressional/Longitudinal Wave

Longitudinal & Transverse Wave Animation Longitudinal & Transverse Wave Animation #2

Combinations of waves Surface waves are a combination of transverse and longitudinal waves. The waves occur at the surface between water and air. Surface Wave Animation Summary of Waves

Summary of Waves - NASA Launch Pad Video Clip

Review, Review, Review… What does a wave carry? How can waves be generated? Compare and contrast a longitudinal and transverse wave.

Properties of Waves

Basic Properties of Waves Amplitude Wavelength Frequency Speed

Amplitude Amplitude is the maximum (displacement) distance the particles of the medium carrying the wave move away from their rest positions. The farther the medium moves as it vibrates the larger the amplitude of the resulting waves. The greater the amplitude the greater the amount of energy

Amplitude of transverse waves The amplitude of a transverse wave is the maximum distance the medium moves up or down from its rest position. You can find the amplitude of a transverse wave by measuring the distance from rest to crest or rest to trough.

Amplitude of a longitudinal wave. The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes.

Wavelength A wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is its wavelength. Transverse measure from crest to crest or trough to trough. Longitudinal measure from one compression to the next.

Frequency The number of complete waves that pass a given point in a certain amount of time. AKA number of vibrations per second. Frequency measured in hertz (Hz) named after Heinrich Hertz who discovered radio waves in Frequency Animation

Period The period of a wave is the time for a particle to make one complete cycle.

Pair Share Is there a relationship between wavelength and frequency? What is it? Is there a relationship between frequency and period? What is it? Is there a relationship between amplitude and frequency? What is it?

Speed The speed, wavelength, and frequency of a wave are related to each other by a mathematical formula. Speed = wavelength x frequency Frequency = speed/wavelength Wavelength = speed/frequency

Speed What can effect the speed of a wave? Wave speed depends upon the medium through which the wave is moving. Only an alteration in the properties of the medium will cause a change in the speed.

1. A teacher attaches a slinky to the wall and begins introducing pulses with different amplitudes. Which of the two pulses (A or B) below will travel from the hand to the wall in the least amount of time? Justify your answer.

They reach the wall at the same time. Don't be fooled! The amplitude of a wave does not affect the speed at which the wave travels. Both Wave A and Wave B travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels.

2. The teacher then begins introducing pulses with a different wavelength. Which of the two pulses (C or D) will travel from the hand to the wall in the least amount of time ? Justify your answer.

They reach the wall at the same time. Don't be fooled! The wavelength of a wave does not affect the speed at which the wave travels. Both Wave C and Wave D travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels.

3. Two waves are traveling through the same container of nitrogen gas. Wave A has a wavelength of 1.5 m. Wave B has a wavelength of 4.5 m. The speed of wave B must be ________ the speed of wave A. a. one-ninth b. one-third c. the same as d. three times larger than

Answer: C The medium is the same for both of these waves ("the same container of nitrogen gas"). Thus, the speed of the wave will be the same. Alterations in a property of a wave (such as wavelength) will not affect the speed of the wave. Two different waves travel with the same speed when present in the same medium.

4. TRUE or FALSE: Doubling the frequency of a wave source doubles the speed of the waves

FALSE The speed of a wave is unaffected by changes in the frequency.

Speed Waves in different mediums travel at different speeds. However, in a given medium and under the same conditions the speed of the wave is constant.

Chapter 15 -3

Ways Waves Interact Reflection Refraction Diffraction Interference Constructive Destructive Standing Waves

Reflection When an object or wave hits a surface through which it cannot pass, it bounces back. Angle of incidence Angle of reflection

Examples of reflection Mirror Echo Ball against a wall

Refraction is when a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium which causes it to bend. The bending of waves due to a change in speed is called refraction.

Refraction Though all waves change speed when they enter a new medium. Bending occurs when one side of the wave enters the new medium before the other side

Diffraction When a wave passes a barrier or moves through a hole in a barrier it bends and spreads out.

Interference Constructive interference occurs whenever two waves combine to make a wave with a larger amplitude. Destructive interference when the amplitudes of two waves combine producing a smaller amplitude.

Standing waves: If the incoming wave and the reflected wave combine at the right places the combined wave appears to be standing still. It appears to be standing in one place, even though it is two waves interfering as they pass through each other. Brightstorm video 9:45 min

Nodes and Antinodes Nodes: at certain points, destructive interference causes the two waves to combine and produce an amplitude of zero. Antinodes are the points of maximum energy. The crests and troughs of a standing wave.

Resonance Most objects have a natural frequency of vibration. Resonance occurs when vibrations traveling through an object match the object’s natural frequency. An object that is vibrating at its natural frequency absorbs energy from the objects that vibrate at the same frequency. Occurs in music.