1. Waves
Pre-AP Physics
Ness

2. So what is a wave?
Everything around us wiggles and jiggles, even things we can’t see such as ATOMS vibrates.
Vibrations can’t exist
in one instant, it has to
move back and forth.
**Just can’t go forward only
or backward only! **

3. Waves
A wave is a disturbance that transfers energy through matter or space or in simple terms…

4. Notice the particle is in the same spot…

5. Waves through a medium
A medium is any substance that a wave can move through.
Example:
Water (ocean waves)
Air (sound waves)

6. Medium

7. Two properties of medium effect the speed of a wave:
Density: waves move slower in a more dense medium.
Elasticity: (think of a rubber band):it returns back to its original shape. Waves move faster if it’s in a more elastic medium.

8. Parts of the wave:

9. Parts of the wave:
1. Amplitude – indicated the energy of the wave – or the height of the wave from origin to crest or from origin to trough.

10. Parts of the wave:
2. Wavelength – distance in meters We use the symbol = λ

11. Parts of the wave:
3. Frequency – is the number of complete waves at a given point (cycle) per time. * We use the unit Hertz or Hz.

12. Types of waves
Longitudinal Waves – movement of the particles are parallel to the motion of the energy – Sound waves
Transverse Waves- movement of the particles are at right angles to the motion of the energy. -Trampoline
Surface Waves- particles travel in a circular motion. – ocean waves

13. Transverse Waves
Transverse waves – the one that we are most familiar with!

14. Longitudinal Wave There are two part of this wave:
Compression- in which the molecules are crowded together.
Rarefaction – molecules are spread out.

15. Longitudinal Waves How does this work?
The compressed band of (air) will move forward colliding with the molecules next to them.
REMEMBER: energy is transmitted as a wave!

16. Ocean Waves
It is a combination of transverse and longitudinal waves.

17. Standing waves Are waves that are trapped between boundaries.
To keep a standing wave going it needs to have a driven end: and end that gives energy to the wave.

18. Nodes and Anti-nodes The places of no amplitude are called NODES.
The places of greatest amplitude are called ANTI-NODES

19. Harmonics
Harmonics have nodes at the boundaries. Harmonics sound louder, keep their energy longer, and take less energy to produce.

20. Earthquakes. Magnitude 7
Earthquakes!!! Magnitude 7.0 HAITI Tuesday, January 12, 2010 at 21:53:09 UTC
A powerful earthquake hit the impoverished country of Haiti on Tuesday, collapsing the presidential palace and numerous other critical government buildings and raising fears of substantial casualties in what a witness called “a major, major disaster.” NBC News

21. Let’s calculate the speed of a wave:
Speed = wavelength X frequency
If you have a wave that has a frequency of 4 Hz and wavelength of 2 meters. What is the speed of the speed?
Steps:
1. Write out the variables
2. Manipulate the equation if needed… Substitute given numbers in the problem
4. Solve for the unknown ( calculate)

22. Now it’s your turn:
What is the frequency of a wave that has a wavelength of 5 meters and a speed of 250 m/sec?

23. Another one…
A wave on a certain guitar string travels at a speed of 200m/s. Calculate the wavelength of an “A” note sounding at 440Hz.

24. Perceived
Shaking
Extreme
Violent
Severe
Very Strong
Strong
Moderate
Light
Weak
Not Felt
Mike Blanpied of the US Geological Survey said that, based on the location and size of the quake, about three million people would have been severely shaken by its impact.

26. Aftershocks
This earthquake was followed by five powerful aftershocks within the first two hours after the devastating quake.
Left: Aftershocks (yellow)
In the first eleven hours after the earthquake there have been 32 aftershocks greater than magnitude 4.

27. Earthquakes
It is produced by sudden motion of rock masses within the Earth’s crust.
The seismic waves of energy radiate outward.
These seismic waves causing the shaking/trembling are known as EARTHQUAKES!!!
**** MOST earthquakes do NO damage at all, very FEW are so extreme!****

28. Seismic Waves
Are detected and recorded by machines called seismographs.
Earthquakes usually produce three types of seismic waves
Primary waves – compression waves
Secondary waves – transverse waves
Surface waves – when a P and S waves reach the surface.

29. Primary Waves
They cause rock particles to move together and apart along the wave direction.
Move through the Earth, can travel through liquids and solids.
The more rigid the matter, the faster it travels through the material.

30. Secondary Waves Can only travel through solid materials.
Cannot be detected by seismographs.

31. Surface Waves
Are slow moving and therefore the last to be recorded on the seismograph.
Cause the greatest and most destructive movement on the Earth’s surface.

32. Behavior of Waves
When waves encounters a boundary of the medium it sometimes reflects, passes through, or change direction.
(Two or more waves can exist in the same medium)
1. We know that waves travel through mediums.
But what happens when that medium runs out?

33. Boundary Behavior
The behavior of a wave when it reaches the end of its medium is called the wave’s BOUNDARY BEHAVIOR.
When one medium ends and another begins, that is called a boundary.

34. Fixed End Here the incident pulse is an upward pulse.
The reflected pulse is upside-down. It is inverted.
The reflected pulse has the same speed, wavelength, and amplitude as the incident pulse.

35. Fixed End Animation

36. Change in Medium
Another condition is when the medium of a wave changes.
Think of a thin rope attached to a thick rope. The point where the two ropes are attached is the boundary.
At this point, a wave pulse will transfer from one medium to another.
What will happen here?

37. Change in Medium
In this situation part of the wave is reflected, and part of the wave is transmitted.
Part of the wave energy is transferred to the more dense medium, and part is reflected.
The transmitted pulse is upright, while the reflected pulse is inverted.

38. Change in Medium
The speed and wavelength of the reflected wave remain the same, but the amplitude decreases.
The speed, wavelength, and amplitude of the transmitted pulse are all smaller than in the incident pulse.

39. Change in Medium Animation
Test your understanding

40. Wave Interaction
All we have left to discover is how waves interact with each other.
When two waves meet while traveling along the same medium it is called INTERFERENCE.

41. Interactions of waves:
INTERFERENCE: when two or more waves arrive at the same point and same time and they interact with each other. They will combine in 2 different ways.

42. results in a larger amplitude results in a smaller amplitude
Types of Interference
Constructive
results in a larger amplitude
Destructive
results in a smaller amplitude

43. Interference
Constructive interference: crest of one wave meets the crest of another wave. You then add together to form a single wave.

44. Interference
2. Destructive interference: when the crest of one wave meets a trough of another wave, they combine by subtracting from each other to form a single wave.

45. Interactions of waves:
There are 3 basic wave interactions: 1. REFLECTION: Bouncing back of a wave after it strikes a boundary that doesn’t absorb the wave’s energy.

46. Law of Reflection
States the angle of incidence is equal to the angle of reflection.
Angle of incidence
Angle of Reflection
Reflected wave – the
wave coming
out
Incident Wave –
The wave coming in

47. Interactions of waves:
2. REFRACTION: remember waves do NOT bend as they travel through a medium they travel in a straight line. But if they travel through DIFFERENT mediums (air-water) or (glass-air), they bend.

48. Refraction:
They bend because the speed of the wave changes as they travel through different mediums.

49. Interactions of waves:
3. DIFFRACTION : bending of waves around the edge of a barrier. New waves forming after the original strikes the barrier.