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

The speed of a wave depends on the medium through which it travels Usually faster in liquids than gases

More particles in a liquid

Exception: Light travels more slowly in liquids than gases

Changes to the medium can affect the wave’s speed Sound travels quicker at warm temperatures than in cool

temperatures

Equation:

Speed=frequency x wavelength

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

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