Introduction to Waves

1. Introduction to Waves

3. Imagine that your family has just returned from a day at the beach. You had a lot of fun, but now you are hungry from playing in the ocean under the hot sun. You put some leftover pizza in the microwave for dinner, and you turn on the radio. Just then the phone rings. It’s your best friend calling to see if you have finished the science homework yet. What is a Wave? A wave is any disturbance that transmits energy through matter or space With a partner, see if you can brainstorm all of the different waves present in this scenario There are at least FIVE different waves! Water waves in the ocean; microwaves inside the microwave oven; light waves from the sun; radio waves transmitted to the radio; and sound waves from the radio, telephone, and voices.

4. Waves Carry Energy As a wave travels, it uses energy to do work on everything in its path. Ex: The waves in a pond do work on the water, and anything floating on the water’s surface, to make it move up and down. Energy can be carried through a wave, however, the material through which the wave travels does not move with the energy. Ex: Sound waves travel through air, but air does not travel with sound

5. Energy Transfer Through a Medium Some waves transfer energy by the vibration of particles in a medium. A medium is a substance through which a wave can travel A medium can be a solid, a liquid, or a gas. Waves that require a medium are called mechanical waves Examples: Sound waves; ocean waves; waves on guitar and cello strings

6. Energy Transfer Without a Medium Some waves can transfer energy without traveling through a medium Waves that do not require a medium are called electromagnetic waves Examples: Visible light; microwaves produced by microwave ovens; TV and radio signals; and X rays used by dentists and doctors Even though electromagnetic waves do not require a medium, they can still travel through substances such as air, water, and glass. However, they travel fastest through empty space.

7. Transverse Waves The highest point of a transverse wave is called a crest Waves in which the particles vibrate with an up-and-down motion are called transverse waves The lowest point of a transverse wave is called a trough Crests Troughs

8. Longitudinal Waves A section of a longitudinal wave where the particles are crowded together is called a compression In a longitudinal wave the particles of the medium vibrate back and forth along the path that the wave travels A section of a longitudinal wave where the particles are more spread out is called a rarefaction

9. Properties of Waves The amplitude of a wave is the maximum distance the wave vibrates from its rest position. Larger Amplitude = More Energy A wavelength is the distance between any two adjacent crests/troughs or compressions/rarefactions in a series of waves Wavelength Amplitude Wavelength Amplitude Wavelength Wavelength Transverse Wave Longitudinal Wave

10. Properties of Waves The number of waves produced in a given amount of time is the frequency of a wave. Higher Frequency = More Energy Shorter Wavelength Longer Wavelength

11. Properties of Waves The speed of a wave depends on the medium in which the wave travels. Waves travel fastest through solids because the particles in solids are close together. Waves travel slowest in gases because the particles in gases are so spread out. The wave speed is the speed at which a wave travels Wave Speed (v) can be calculated using wavelength () and frequency (f) in the following equation: v =  x f (wave speed = wavelength x frequency)