Objective 5 – Motion Forces and Energy (IPC 5)

IPC (5) (A) – Demonstrate wave types and their characteristics

We encounter waves everyday. When we hear the word “wave” we tend to think of surfer dudes. However, we don’t need to be near water to experience waves

One common type of wave is longitudinal, or compressional wave. In a longitudinal wave, the particles of the wave move parallel to the direction of the wave. Sound is a longitudinal wave.

For a transverse wave, the particles move perpendicular to the direction of wave. Your favorite radio station transmits transverse waves.

Two properties of waves are wavelength and frequency. For a longitudinal wave, a wavelength is the distance between successive compression.

For a transverse wave, a wavelength is the distance between two successive crests (or troughs). Like all distances, wavelength is measured in meters.

The frequency of a wave is the number of waves that pass a point in space in a given time period. So if 5 waves pass a point in 1 s, the frequency of the wave is 5 waves per second or 5 Hertz (Hz).

The product of the frequency and wavelength is the speed of the wave. Where v is the speed, f is the frequency and λ (lambda) is the wavelength. The speed is measured in m/s.

Heerzwun: A sound wave has a frequency of 256 Hz and wavelength of 1.3 m. What is the speed of the wave?

UTri: Two water waves strike the edge of a dock every second (What does this statement describe?). The speed of the wave is 6 m/s. What is the wavelength?

IPC (5) (B) – Students will demonstrate wave interactions including interference, polarization, reflection, refraction, and resonance.

Waves interact with matter and with themselves. They are very social.

One form of interaction is interference. Interference occurs when two or more waves occupy the same point in a medium at the same time.

Interference of waves may be constructive or destructive. When constructive interference occurs, the amplitude of the combined waves increases (i.e. sound gets louder or light becomes brighter).

When destructive interference occurs, the amplitude of the combined waves decreases (so what happens to the volume of sound and the intensity of light?)

Polarized waves are transverse waves that are in the same plane. Notice, the vertical wave may pass through the vertical analyzer and the horizontal wave may pass through the horizontal analyzer.

What happens when the vertical wave is incident upon the horizontal analyzer?

Reflection of waves enables us to see the world around us. An important property of a wave is called the Law of Reflection.

The Law of Reflection states that for any reflected wave, the angle of incidence (the angle at which the wave arrives, measured from the normal) is equal to the angle of reflection (the angle at which it leaves, also measured from the normal).

Most of the reflection of light we see is scattered (or diffuse). The light is reflected from an object in every direction. Some of the light enters our eyes enabling us to see that object.

Light is reflected from a mirror or still body of water is regular reflection. All of the waves incident on the surface that are parallel to each other are also reflected parallel to each other.

This type of reflection enables us to see images in the surfaces.

If you view an object on the bottom a swimming pool, the object appears to be closer to the surface than it actually is. This phenomenon is described as refraction.

Refraction is the bending of light as it passes from one optical medium to another, like air to water or glass to air. How does refraction cause a straw in a glass of water to appear to be split into two sections?

Is it possible for a operatic soprano to shatter a glass by singing a very high pitch?

Actually, it is. This is an example of resonance – two objects vibrating at the same natural frequency. Almost all objects have a natural frequency at which they vibrate (glasses, loose wheels on grocery carts, stadium bleachers, bridges, etc.).

If one object vibrates at the same frequency of a second object, this resonance increases the amplitude of the vibration.

Describe the resonance in each case A child “pumps” his legs while swinging on a swingset A crowd rhythmically stomps and sways causing stadium bleachers to collapse One person “rockets” another on a trampoline (causing the second person to break her arm, thereby suing the first person)