Chapter 1: Characteristics of Waves Section 1: What are Waves Sound and Light Chapter 1: Characteristics of Waves Section 1: What are Waves 3: 38.08/58 = 60.48% 5: 46.05/58 = 79.40% 6: 45.80/58 = 78.97%

Vocabulary Wave Energy Medium Mechanical Wave Vibration Transverse wave Crest Trough Longitudinal wave Compression Rarefaction

Waves and Energy A wave is a disturbance that transfers energy from place to place. Remember, energy is the ability to do work. Think about a raft on the water Wave disturbs surface as well as raft. But the disturbance caused by the wave is temporary, and the wave passes, and raft returns to normal. Most kinds of waves require something to travel though. The material through which a wave travels is called a medium. Waves that require a medium are called mechanical waves. Waves that don’t require a medium are called electromagnetic waves

How do waves transfer energy? Although mechanical waves travel though a medium, they don’t carry the medium with them. The wave just makes the medium move back and forth, it is the energy that is getting transferred. Think of the “wave” at a sporting event

What causes waves? Energy is always required to make a wave. Mechanical waves are produced when a source of energy causes a medium to vibrate. A vibration is the repeated back and forth or up and down motion. When a vibration moves through a medium, a wave results. Remember, anything that moves has energy, so a moving object can give its energy to a medium, and make a wave.

Types of Waves Transverse Waves Waves that move the medium at right angles to the direction the wave travels. As a transverse wave moves, the particles of the wave move at right angles to the direction of the wave.

Compression is where the medium is close together Longitudinal Waves These waves move the medium parallel to the direction in which the wave travels. Compression is where the medium is close together Rarefactions are where the medium is far apart.

We can use diagrams to represent transverse and longitudinal waves.

Chapter 1: Characteristics of Waves Section 2: Properties of Waves Sound and Light Chapter 1: Characteristics of Waves Section 2: Properties of Waves

Vocabulary Amplitude Wavelength Frequency

Amplitude Remember, all mechanical waves move medium. The distance the medium moves depends upon the amplitude. Amplitude is the maximum distance that the particles of the medium carrying the wave move away from their rest positions. More energy = Greater Amplitude For transverse waves: Amplitude is the maximum distance up or down the wave moves. Higher/lower waves = greater amplitude For longitudinal waves: Amplitude is the measure of how compressed or rarefied the medium becomes. Dense compressions = greater amplitude

Wavelength Wavelength A wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is the wavelength. Transverse Wave: Wavelength can be found by measuring distance from crest to crest or from trough to trough. Longitudinal Wave: Wavelength can be found by measuring distance between compressions.

Frequency Wave frequency is the number of complete waves that pass any given point in a certain amount of time. If I make waves in a rope so that one wave passes a given point every second, the frequency of the wave is 1 wave per second. Frequency is measured in unit of hertz (Hz) The wave above would have a frequency of 1 Hz.

Speed of Waves Different waves travel at different speeds. The speed of a wave is how far the wave travels in a given length of time Or the distance divided by the time it took to travel that distance.

Relating Ideas Speed, wavelength and frequency are mathematically related. Speed = Wavelength x Frequency Wavelength = Speed / Frequency Frequency = Speed / Wavelength

Chapter 1: Characteristics of Waves Section 3: Interactions of Waves Sound and Light Chapter 1: Characteristics of Waves Section 3: Interactions of Waves

Vocabulary Reflection Refraction Law of reflection Diffraction Interference Constructive Interference Destructive Interference Standing wave Node Antinode Resonance

Reflection When a wave hits a surface though which it cannot pass, it bounces back. This interaction is called reflection All waves obey this. The law of reflection states that the angle of incidence equals the angle of reflection.

Refraction When a wave moves from one material to another, it encounters a change in wave speed. If the wave is at an angle, one side change speed before the other, causing it to bend. This bending of waves due to a change in speed is called refraction. Again, the wave MUST enter an angle for this to occur

White light and refraction White light is made of lots of different frequencies of light When white light refracts, each color bends by different amounts. This separates the colors Rainbows!

Diffraction When a wave moves around a barrier or after it passes through a narrow channel it will bend and spread out. This is called diffraction. Like refraction, it involves the bending of waves. Unlike refraction, does not pass through any new materials.

Interference Interference is an interaction that occurs whenever two waves meet. Two types of interferences Constructive Interference Occurs when two waves combine to make a wave with a bigger amplitude Occurs when crests of one wave overlap with crests of another wave (or troughs and troughs) Destructive Interference Occurs when two waves combine to make a wave with a smaller amplitude Occurs when crests of one wave overlap the troughs of a 2nd wave. If crest is larger than trough, then resultant wave will have a smaller crest If trough is larger than crest, the resultant wave will have a smaller trough

Interference Applets

Standing Waves A special occurrence when interference occurs after wave reflection has occurred. If the incoming wave and reflected wave have just the right frequency, they will produce a combined wave that appears to be standing still. This combined wave is called a standing wave. So a standing wave is really two waves interfering as they pass through each other, that appears to be standing still.

Nodes and Antinodes In a standing wave, destructive interference produces points with no amplitude. These points of zero amplitude on a standing wave are called nodes. Nodes are always evenly spaced on the standing wave. Also in a standing wave, constructive interference creates points with great amplitude. These points of maximum amplitude are called antinodes. Antinodes are also ½ between nodes.

Standing Wave Demonstrator

Resonance Most object have a natural frequency. A swing that is pushed at the swing’s natural frequency allows a small push to create a large increase in the swing’s amplitude. Standing waves occur when an object vibrates at its natural frequency. If a nearby object vibrates at the same frequency as an object’s natural frequency, resonance can occur. Resonance is an increase in the amplitude of a vibration that occurs when external vibrations match an object’s natural frequency. Can be useful Musical instruments use resonance o create stronger, clearer sounds.

Resonance can be harmful Tacoma Narrows Bridge