Wave Interactions Describe refection, refraction, diffraction, and interference Compare destructive interference with constructive interference Describe resonance, and give examples

All stars, including the sun, produce light. Planets and the moon do not produce light. Why do planets and the moon shine so brightly in the evening sky?

Reflection occurs when a wave bounces back after striking a barrier. All waves—including water, sound, and light waves—can be reflected. Reflected sound waves are called echoes, and light waves reflecting off an object allow you to see that object. Light waves from the sun are reflected when they strike the surface of the moon

The mountain reflects off of the water

Refraction is the bending of a wave as it passes at an angle from one medium to another The speed of a wave varies depending on the medium in which the wave is traveling. When a wave moves from one medium to another, the wave’s speed changes.

Have you ever placed a pencil in a glass of water? The pencil appears to be broken into two pieces. When you take the pencil out of the water, it is perfectly fine.

The stick appears to bend in the water This is an example of refraction

Imagine you are walking and you hear music The sound seems to be coming from around the corner, but you cannot see who is playing the music because a house blocks your view. Are the sound waves bending around the corner?

Most of the time, waves travel in straight lines A beam of light from a flashlight is fairly straight Sometimes waves curve or bend when they reach the edge of an object. diffraction The bending of waves around a barrier or through an opening is known as diffraction

The amount of diffraction a wave experiences depends on its wavelength and the size of the barrier or opening the wave encounters

If you compare sound waves with long wavelengths to light with shorter wavelengths then you can understand why you can hear music around the corner of a building but are not able to see who is playing the music. Long wavelengths are more affected by diffraction than are short wavelengths.

Because waves are energy and not matter, more than one wave can exist in the same place at the same time. In fact, two waves can meet, share the same space, and pass through each other. When two or more waves share the same space, they overlap. The result of two or more waves overlapping is called interference.

When sound waves from several instruments combine through interference, the result is a wave with a larger amplitude, which means a louder sound.

Constructive interference occurs when the crests of one wave overlap the crests of another wave or waves. The troughs of the waves also overlap The resulting wave has a larger amplitude than the original waves had.

Destructive interference occurs when the crests of one wave and the troughs of another wave overlap The resulting wave has a smaller amplitude than the original waves had

RESONANCE When you push someone on a swing you have to time your pushes to the time for the swing to move back and forth. By continually adding energy to the swing in small pushes, the size of the swing gradually builds up to a large amplitude. RESONANCE occurs when a series of small pushes with the right timing and causes an object to build up a large amount of energy.

Example of resonance You may notice something vibrate loudly in the car only when driving a certain speed. At that speed the vibration from the engine is timed just right so that each vibration adds properly to the energy of the object, until it is vibrating with a large amplitude. At other speeds the timing isn't right and vibrations don't build up.

Resonance was partially responsible for the destruction of the Tacoma Narrows Bridge The wind caused vibrations that were close to a resonant frequency of the bridge

Because the bridge was in resonance, it absorbed a large amount of energy from the wind, which caused it to vibrate with a large amplitude