A wave is an oscillation that transmits energy through a medium.

Waves do not transmit matter, only energy.

A pulse is like a wave, but only a single disturbance.

wave

medium

examples

sound

matter (solid, liquid, gas)

talking, music

light

electro-magnetic fields

sunlight, wifi

surface

interface between two media

ocean waves, ripples

string

string

whip

traffic

cars on a road

the 405 @ 5:00pm

seismic

solids

S and P waves

gravitational

spacetime

LIGO

electrical

wires

cable TV, phone lines

Interference

Two waves pass through each other without any effect.

Wave Properties

amplitude = m velocity
= m/s wavelength =
m

frequency = Hz period
= s

Frequency and period have a mathematical relationship. Let's see if we can build an equation for how they are related.

Use the simulator above to record five different pairs of frequency and period. Graph the pairs with period as the x-coordinate
and frequency as the y-coordinate. What does the graph look like?

$$f = \frac{1}{T}$$

\(f\) = frequency [Hz, s⁻¹, hertz]
How often an event happens in a second.

\(T\) = time period [s, seconds]
How many seconds are between each event.

Frequency and period are the inverse of each other. If a wave has a frequency of 2Hz, then 2 wavelengths pass a point in
a second, but the period is 1/2s because that is the time for a single wavelength to pass.

Click to Run

The Wave Equation

$$v = f \lambda \quad \quad v = \frac{\lambda}{T} $$

\(v\) = wave speed [m/s]
\(\lambda\) = wavelength [m, meters]
\(f\) = frequency [Hz, s⁻¹, hertz]
\(T\) = time period [s, seconds]

speed

vacuum

air

water

glass

sound (m/s)

N/A

340

1,484

4,540

light (m/s)

300,000,000

300,000,000

220,000,000

200,000,000

Example: An air horn sounds at a frequency of 220 Hz. What is the wavelength of the sound wave?
solution

Example: The distance between successive crests in a series of water waves is 4.0 m, and the crests travel
8.6 m in 5.0 s. Calculate the frequency of a block of wood bobbing up and down on these water waves.
solution

Example: Two students are holding a slinky while standing 3.6 m apart. The first student sends a pulse
which travels all the way down and back again. It takes 2.4 s for the wave to return. What is the speed of the wave?
solution