The Nature of Waves

Energy can be transferred by the movement of an object

e.g. Moving matter.

Continued

Energy can also be transferred when it is carried through a substance.

http://www.youtube.com/watch?v=bMgBt-UuUak

Solar Tsunami

Mechanical Waves (energy through matter)

• All waves involve the transfer of energy without a net transfer of matter.

• The substance carrying the wave is called the medium.

• In the case of the tsunami, the medium is the water of the ocean.

• In the case of the sound waves from the speaker, the medium is the air.

Mechanical Waves

Mechanical waves are generated at a source and must be passed through an elastic medium

Source of the sound waves comes from vibrating guitar string.

Why combine the study of waves and light?

If waves are to be our chosen model for light then they must appear to behave largely in the same manner as light. That is, if a wave model for light is to be accepted then it will need to be able to explain the known behaviours of light. A very successful model would illustrate all of the behaviours of light. Perfect modelling is rare in science. Rather it is more likely that we make use of the insight that a particular model provides and, as was the case with our early models of the atom, use it as a stepping-stone to furthering our understanding.

Sound Waves From A Speaker

http://www.youtube.com/watch?v=UU7iuJ98fRQ&feature=related

http://www.youtube.com/watch?v=scbPKjU8Ssg&feature=related

http://www.youtube.com/watch?v=Yw4qklgNIxI&feature=related

http://www.youtube.com/watch?v=3zoTKXXNQIU&feature=fvw

Slinky Springs

• Create a single wave using a slinky spring.

• Create a continuous wave using a slinky spring.

Wave Pulses and Continuous Waves

A wave pulse occurs when a single disturbance passes through a medium

Continuous waves are produced when there is repetition (oscillation) at the wave source.

Time to play with slinky springs

Transverse and Longitudinal Waves

Transverse waves are produced when the direction of vibration is at right angles to the direction of the wave energy.

Transverse and Longitudinal Waves

• Longitudinal (compression) waves are produced when the direction of vibration is parallel to the direction of the wave energy.

S and P waves associated with earthquakes

Which of the S and P waves is longitudinal? Which is transverse?

Longitudinal Waves

Sound Waves are an example of Longitudinal Waves

One, Two and Three Dimensional Waves

One dimensional waves occur when energy travels along the length of the conducting medium.

Example: wave in spring or rope.

Two dimensional waves occur when energy spreads in two dimensions.

Example: wave in ripple or a pond. Solar quakes seen earlier.

Example of two dimensional wave

http://www.youtube.com/watch?v=2awbKQ2DLRE

Three Dimensional Waves

Three dimensional waves occur when energy spreads out in all directions.

Example: sound waves when you speak.http://www.youtube.com/watch?v=s9GBf8y0lY0

Example: pressure waves from a bomb blast.http://www.youtube.com/watch?v=nyaQnhvZMxI

Summary• Scientists use models to link an unknown entity or observation to something that we are familiar with, in order to gain a better understanding of it.

• Knowledge of general wave properties will allow the possible wave nature of light to be assessed.

• Energy must be present at the source of any wave.

• All waves involve the transfer of energy without a net transfer of matter.

• A substance carrying a wave is called a medium.

• A mechanical wave is the passing of energy from one particle to the next within an elastic medium.

• A wave pulse occurs when a single disturbance is passed through a medium.

• Continuous waves are created when there is a repetitive motion or oscillation at the wave source. Energy is carried away from the source in the form of a continuous or periodic wave.

• Longitudinal waves occur when particles of the medium vibrate in the same direction as the direction of travel of the energy.

• Transverse waves are created when the direction of the vibration of the particle of the medium is perpendicular to the direction of travel of the wave energy itself.

7.1 Questions

Do them now…