Waves and vibrations

Waves

Rogue wave

DEFINITION OF A WAVE

What is a wave?

• Is a disturbance that carries energy through matter or space

• It may or may not need a medium to move through, depending on the type of wave

Does a floating object move with the ripple?

Response

• Though the object will move as the ripple moves underneath, the extent of motion is much less than the wave it self

DEFINITION OF A MEDIUM

Medium

Is any material through which a wave passes through

Mediums move only a small amount compared to the distance the wave travels

In general the medium returns to its original position, after the energy of the wave has passed

WHAT IS A VIBRATION?

An object vibrates when every portion of object repeats its motion

along a simple path over a measurable length of time

Vibrations

• Involve transformations of energy• Potential to Kinetic and back

• Think of a weight on the spring

Cause of a vibration

• Repeated application of forces on an object or medium

Another name for this type of motion is…

• Periodic Motion

• Any motion that repeats in a regular cycle

WAVES AND ENERGY

Waves transfer energy

• We know waves transfer energy because they do Work

• Water waves boat, leaf, surfer…• Sound waves eardrum• Light waves on your eye, photographic film

Have you ever been hit by an ocean wave?

• Then you can get the idea that ocean waves can carry a lot of energy.

• Research is underway to find ways to harness energy of ocean waves

• Some of this research is being done at the university of Delaware

Energy from Ocean Waves

• June 2007

Wave Energy Bill Approved by U.S. House Science Committee

Washington, DC [RenewableEnergyAccess.com]

The U.S. House of Representatives Science and Technology Committee has approved, by voice vote, renewable energy legislation that would invest approximately $200 million in federal

funds to advance research and development of wave energy technologies over the next four

years.

Tsunamis

• Huge ocean wave caused by massive displacement of water

WHAT IS PERIODIC MOTION ?Simple Harmonic motion

Periodic motion is broadly defined

• Includes items moving in circles

• More interested in subsection that deals back and forth motion

• Simple harmonic motion

SIMPLE HARMONIC MOTION

Simple harmonic motion• Examples: Slinky, swings, Bungee divers (hopefully)

• Object starts at equilibrium (balanced forces)

• As object is pulled away from equilibrium, the force trying to bring it back (restorative) increases

• Restorative force is directly proportional to displacement from equilibrium point

• Motion is periodic and repetitive

Damped Harmonic Motion

• The up and down motion fades over time

• Result of Friction, Air resistance or internal mechanisms

• Can be advantageous

TYPES OF WAVES

Mechanical Waves

• Waves that need a medium to move through

• A mechanical wave is a series of energy pulses that pass through matter

• Any vibration in matter is the source of a mechanical wave.

Examples of mechanical waves:

• Sound• Water wave• earthquake

DIFFERENT MECHANICAL WAVES MOTION

Mechanical waves

Transverse wave Longitudinal wave

Transverse waves

• Waves in which the motion of the particles is perpendicular to the motion of the wave (energy)

• Vibration is perpendicular in direction to motion of energy

• The “wave” that travels around a stadium

Demo of transverse waves

Longitudinal waves

• Direction of force is parallel to direction of pulse

• Direction of vibration is parallel to direction of energy

• Compression and rarification in medium

• Example: Sound

Rarification

• A region in a medium where the density of matter is decreased

• Medium is stretched or thinned

WHAT DOES THE SECTION OF SLINKY WANT TO DO AS YOU COMPRESS IT?

Answer

• The rest of the slinky pulls back, until it reaches the equilibrium point

• If the slinky section overshoots, it will be pulled back in the other direction

• Simple harmonic motion

Surface waves

• Occur at boundaries between two different medium

• Combination of the two

• Particles in the medium roll or take a circular path

• Example: Ocean waves, Surface wave of an earthquake

What are the types of waves that do not need a medium to move ?

ELECTROMAGNETIC WAVES

Electromagnetic waves• Light travels through space which does not contain

matter in all places

• An electromagnetic wave does not need a medium to pass through a space.

• Additional examples of electromagnetic waves, x-rays, microwaves, ultraviolet light, infrared radiation, gamma rays…

• More about these when we discuss light

Difference in waves

• Related to the different ways that energy is transferred.

• Mechanical waves require a mechanical force to transfer the energy (things bumping into each other)

• The energy from Electromagnetic waves is absorbed by a atom and then readmitted

Difference in speed

• Electromagnetic are much faster

• As the medium gets denser, mechanical waves tend to get faster, electromagnetic waves tend to slow down