Physics 11: Mr. Jean June 4th, 2012

The plan: Video clip of the day Bow waves What makes a good surfing day Visible spectrum Doppler Effect Shock Waves Speed of sound Lab soon!

Doppler Effect: http://www.brightstorm.com/science/physics/vibration-and-waves/doppler-effect/

BOW WAVES Waves in front of moving object pile up. The familiar bow wave generated by a speedboat knifing through the water is a non-periodic wave produced by the overlapping of many periodic circular waves. It has a constant shape.

Sonic Boom: Just as circular waves move out from a swimming bug, spherical waves move out from a flying object. If the object flies faster than the waves, the result is a cone-shaped shock wave. There are two booms, one from the front of the flying object and one from the back.

At the speed of sound: Subsonic x x x x x x

Supersonic x x x x x x x x x x x x x

Video Demonstrations: Sonic Boom video

Subsonic - slower than the speed of sound Supersonic - faster than the speed of sound speed of object Mach Number = speed of sound

Standing Waves: http://www.brightstorm.com/science/physics/vibration-and-waves/standing-waves/

Speed of Sound: The speed of a sound wave refers to how fast the disturbance is passed from particle to particle; speed refers to the distance in meters which the disturbance travels per unit of time in seconds.

The speed of a sound wave in air depends upon the properties of the air, namely the temperature and the pressure. v = 331 m/s + (0.6 m/s/C)•T where T is the temperature of the air in degrees Celsius. Using this equation to determine the speed of a sound wave in air at a temperature of 20 degrees Celsius yields the following solution.

Calculations for 20 degrees:

Is seeing really believing?

Speed of Sound Lab: Complete Speed of sound lab. 4 people per group. All group members are responsible for a completed lab. Staple all labs together and marking top lab only.

Good Surf Days: There are two main factors that determine how good the surf will be. 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. 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: There are three main factors Wind Speed - The greater the wind speed the larger the wave. Wind Duration -The longer the wind blows the larger the wave. Fetch - The greater the area the wind affects the larger the wave.

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: How Waves Are Made 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.

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

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.

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. 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."

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

When everything is right:

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