12.4 Wave Interactionspp. 459 - 465

Mr. Richter

Agenda

Warm Up Check and Review HW Schedule Update:

Today- 12.4.1 and Finish Lab

Tomorrow- 12.4.2 Thursday- Problem

Solving Practice Friday- Review

Monday- Test

Notes: Interference Superposition Reflections

Finish Collecting Data Start Reading

Objectives: We Will Be Able To… Apply the superposition principle. Differentiate between constructive and destructive

interference. Predict when a reflected wave will be inverted. Predict whether specific traveling waves will produce a

standing wave. Identify nodes and anti nodes of a standing wave.

Warm-Up:

Why do you think some frequencies make standing waves in the vibrating string, and other frequencies do not?

Wave Interference

Wave Interference

When waves collide, they occupy the same place at the same time. Think about two sounds happening at once.

This can happen because mechanical waves are not actually matter, they just displace matter.

In addition, waves pass unaffected by each other after they collide.

Wave Interference

The combination of two overlapping waves is called superposition.

The superposition principle: When two wave pulses collide, their amplitudes are added together to form a resultant pulse

http://www.youtube.com/watch?v=YviTr5tH8jw

Constructive Interference

If the displacement of the two pulses is on the same side of equilibrium, they have the same sign.

The resultant displacement (sum of the pulses) is larger than either of the original pulses.

http://www.youtube.com/watch?v=YviTr5tH8jw

Destructive Interference

If the displacement of the two pulses are on opposite sides of equilibrium, they have opposite signs.

The resultant displacement (sum of the pulses) is smaller than both of the original pulses.

http://www.youtube.com/watch?v=URRe-hOKuMs

Reflections

Reflections

When waves reach a boundary, they are often reflected back (or in some other direction).

Like echoes. And mirrors.

Reflections at “Free” Boundaries

If the end of the medium is free to move, it behaves as if it is whipped back the other way.

The return wave is identical to the original pulse.

Like sound waves in a trumpet.http://www.youtube.com/watch?

v=aVCqq5AkePI

Reflection at “Fixed” Boundaries

If the end of the medium is fixed (cannot move), then the wall exerts an opposite downward force on the medium.

The pulse wave is inverted after the reflection.

Like a plucked guitar string.http://www.youtube.com/watch?

v=LTWHxZ6Jvjs

Wrap-Up: Did we meet our objectives?

Homework