IB Physics 11 Vibrations and Waves Mr. Jean January 6 th, 2014

The plan: n Video Clip of the day n Wave interference

In symbolic form or

For a wave, if the distance traveled is a wavelength ( ), then the time to travel this distance is the period (T). Then or

5.TRANSVERSE WAVES Demonstration: Transverse Waves Examples: string musical instruments ripples on water electromagnetic waves

6.LONGITUDINAL WAVES Video - Slinky Longitudinal Waves Parameters Rarefactions are regions of low density. Compressions (condensations) are regions of high density.  is the distance between successive rarefactions or successive compressions.

7.INTERFERENCE Video - Superposition of Waves SlideSlide - Interference Slide

Constructive interference occurs when waves are in phase, that is when crests are superimposed and troughs are superimposed.

Destructive interference occurs when waves are out of phase, that is when crests are superimposed with troughs.

Interference is a characteristic of all waves. Demonstrations with Audacity

Standing Waves n n When two sets of waves of equal amplitude and wavelength pass through each other in opposite directions, it is possible to create an interference pattern that looks like a wave that is “standing still.” It is a changing interference pattern. n Demo - Rope and strobe n Demo - Mechanical overhead model

n There is no vibration at a node. n n There is maximum vibration at an antinode.  is twice the distance between successive nodes or successive antinodes.

Good Surf Days: n There are two main factors that determine how good the surf will be. u First, there are the conditions that lead to initial wave formation. These determine the quality and size of the ground swell that will hit the surf spot. u The second main factor is the local conditions at the surf spot. These have to be right to ensure the swell can create quality waves. Let's look at both of these factors in turn.

Factors which produce waves: n There are three main factors u Wind Speed - The greater the wind speed the larger the wave. u Wind Duration -The longer the wind blows the larger the wave. u Fetch - The greater the area the wind affects the larger the wave.

n Closely packed isobars (areas of equal pressure shown on a weather map) mean strong winds. It is these deep low pressures that generate the big swells. The swell will be bigger and last longer...

Making the waves: n How Waves Are Made u Waves are generated by wind. Offshore storms generate winds which blow on the surface of the sea and create ripples, much in the same way as the ripples in your post surf cuppa are made when you blow on it to cool it down.

n Where it all begins: u Offshore storms generate winds. u The ocean would be almost completely flat without wind.

n The stronger and longer the wind blows, the more effect it has on these ripples and the larger they become. Initially the waves will just be small chop, but these will soon increase in size.

n As the wind continues to blow and the waves generated remain under the influence of the wind, the smaller waves will increase in size. The wind will get hold of the small waves much more easily than the calm sea surface. n The wave size is dependent on the wind speed generating it. A certain wind speed will only be able to generate a wave of certain size. Once the largest waves that can be generated for a given wind speed have formed, the seas are "fully formed."

n The longer period waves are faster and move farther ahead of the rest of the slower waves. n As the waves travel farther away (propagate) from the wind source, they start to organise themselves into swell lines. u Swells are essentially "Wave trains"

When everything is right:

Nova Scotia n Nova Scotia is quickly becoming a surf destination for surfers around the world. u Especially late August into October for hurricane season.

More properties of waves:

Reflection to fixed ends (Rigid): n For fixed end reflection think of the medium as being constrained in its motion. n In the picture to the left you see a string that is securely fixed to the wall. n The string (the old medium) is free to move up and down, but at the boundary where it meets the new medium (the wall) it is constrained – the string can’t really move up and down like it could before. n In fixed end reflection, the wave that is reflected back is out of phase by 180 .

Reflection for non-fixed (not rigid… “open”): n In free end reflection, the medium is free to move at the boundary. The reflected wave will be in phase. In the drawing on the right, you see an erect pulse traveling into the boundary being reflected with no phase change. The pulse went in erect and came out erect. Water waves reflecting off a solid wall are a good example of free end reflection.

Sound Waves: n The disturbance which travels through air is the compression of air molecules – they are squeezed together and pulled apart. Sound is a series of traveling high pressure and low pressure fronts.

Pressure vs. Time

Wave Videos: Bright Storm: EXCELLENT PHYSICS VIDEOS n 1B F9D 1B F9D 1B F9D