Unit: Waves & Sound

Topic: Vibrations & Waves

Question How many of you know about

periodic motion? It is everywhere in the world - your heart - your breathing - drinking orange juice

- What else?

Topic: Vibrations & Waves

Explain… Observe… Explain…

Where have you seen waves before?

WavesWave Types: Mechanical (through media)

• Ocean waves• Sound Waves• Flapping Flag

Electromagnetic (through space)• Light• X-ray• Ultraviolet• Infrared• Radio waves• Microwaves

WavesWaves transfer energy over a distance in

the form of a disturbance. This disturbance can be caused by the vibration of an object. A vibrating object has a ‘rest’ position and will periodically shift from this state to another. Think of the type of vibrational motion exhibited in the following examples.

A weight hanging from a spring.A weight hanging from a rope and the rope is twisted. A pendulum. A piece of wood floating in the ocean.Periodic motion occurs when an object repeats a pattern of motion. The vibration, or oscillation is repeated over and over with the same time interval.

Types of VibrationsThere are 3 basic types of vibrations: transverse vibrations, longitudinal vibrations, and torsional vibrations.

A transverse vibration occurs when an object vibrates perpendicular to its axis at the normal rest position (such a pendulum).

A longitudinal vibration occurs when an object travels parallel to its axis at the rest position.

A torsional vibration occurs when an object twists around its axis at the rest position, for example a human twisting to the left or the right periodically.

Observe the twist to the left, then the rest position, then the twist to the right.

Measuring Vibrations All waves are caused by vibrations f = # of cycles / ∆t Frequency is measured in Hertz

(Hz) 1 Hz = 1 cycle / second

1 cycle = the time it takes to go from here

To here

And then back again

Cycle

Period Period is the amount of time for a

single vibration to occur. T= (1/f), T= (Δt)/(# of cycles) Period is measured in seconds

The distance in either direction from the equilibrium, or rest position to maximum displacement is called the amplitude (A) of vibration.

Objects that are ‘in phase’ vibrate with the same period and pass through the rest position at the

same time and in the same direction.

In Phase In Phase Out of phase

In small groups I would like you to illustrate to me one of the

types of vibrations you learned today with any of the materials/resources you have in this class….

Calculate the following: - the frequency - the periodYou will make up the # of cycles & time you so

desire 1 person can be a timer 1 person can be the person who counts the cycles 1 person can be the recorder