# Waves. What is a wave?  Repeating disturbance that transfers energy through matter or space  Waves in water  Sound  Light  When traveling through.

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Waves

What is a wave?  Repeating disturbance that transfers energy through matter or space  Waves in water  Sound  Light  When traveling through matter, they are caused by particles transferring energy to other particles  The wave does not “move”  It transfers energy causing particles around it to move  Waves carry energy without transporting matter

Making Waves  Waves only travel as long as they have energy  As the energy is lost, the waves decrease in size  All waves are due to vibrations  Movement up and down, or back and forth

Mechanical Waves  Waves that can only travel through a medium  Medium=matter through which a wave travels  Sound waves, water waves, and other waves we can see are mechanical waves

Transverse waves  A wave where particles in the medium move back and forth at right angles to the direction of the wave

Longitudinal waves  Waves in which the particles move back and forth  Same direction as the movement of the wave  Most of the waves we cannot see  Sound waves

Seismic Waves  Caused by the movement of Earth’s Crust

Properties of Waves  Parts of a wave  Transverse waves:  Crest-high points  Trough-Low points  Longitudinal waves:  Compression- more dense region  Rarefaction- less-dense region

Wavelength  The distance between one part of the wave, and the next just like it  Represented by Greek letter lambda (λ)

Frequency and Period  Frequency-number of wavelengths that pass a fixed point each second  Measured in Hertz (Hz)  1 Hz= 1/s  Related to frequency  Longer wavelengths have longer frequencies  More small waves pass through a point than longer waves  Period  Amount of time it takes one wavelength to pass a point in seconds

Wave Speed

Amplitude  Measure of the size of the disturbance of a wave  In longitudinal waves,  High-amplitude waves have compressions closer together and rarefactions farther apart  Low-frequency waves have compressions further apart and rarefactions closer together  In transverse waves,  From the rest position to the crest or trough

Reflection  Occurs when a wave strikes an object and bounces off of it

The Law of Reflection  Beam hitting the object is the incident ray  The reflected beam is the reflected ray  The perpendicular line between them is the normal  i is the angle of incidence  r is the angle of reflection  The Law of reflection states that i and r are equal

Practice  A laser hits a mirror at 25 degrees to the normal. What will be the angle of reflection to the normal?  25 degrees

You try it  A beam of light hits a mirror at an angle of 10 degrees from the mirror. What is the angle of reflection from the normal?  80 degrees

Refraction  Bending of waves due to change in speed from one medium to another  When light slows down, it bends toward the normal  When light speeds up, it bends away from the normal

Diffraction  The bending of waves around an object

Interference  Multiple waves overlap and combine to form a new wave  Constructive interference: Waves add together  Destructive interference: Waves subtract from one another

Standing Waves  Occurs when waves equal in wavelength and amplitude, but in opposite directions, constantly interfere with each other  https://www.youtube.com/watch?v=no7ZPPqtZEg https://www.youtube.com/watch?v=no7ZPPqtZEg  The waves appear not to move  Standing waves have nodes  Places where interfering waves always cancel  Used in instruments to produce pure sounds

Resonance  Process by which an object is made to vibrate by absorbing energy at its natural frequency  Swinging on a swing (have to pump at the right time to speed up)  https://www.youtube.com/watch?v=wvJAgrUBF4w https://www.youtube.com/watch?v=wvJAgrUBF4w

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