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 waveLongitudinal 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