Lecture_18

Lecture_18 - 16.3 The Speed of a Wave Lets look at a...

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16.3 The Speed of a Wave Let’s look at a transverse wave propagating toward a wall: The speed of the wave will depend on how fast the segment of string at point 1 can pull up on the segment of string at it2 point 2. By Newton’s 2 nd Law, F = ma , so a greater force means a greater acceleration, and thus a faster moving wave. But what is the force in this case for the wave on a string??? It’s the tension in the string! Thus, the greater the tension in the string, the faster waves will move on the string. But, the acceleration of each mass segment of string, also depends on the mass of the string. The lighter each mass segment of string, the greater the acceleration, and thus speed. For a continuous medium, like a string, rope, wire or cable, we can use Mass Density.
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Length Mass Density Mass = L M = ρ For small amplitude waves propagating along a continuous media, the speed of the wave is given by: L F v = m FL = F is the tension force along the media (string, rope, etc.) Example : To measure the acceleration due to gravity on a distant planet, an astronaut hangs a 0.125-kg ball from the end of a wire. The wire has a length of 0.75 m and a ear density of 7 9 × 0 -4 g/m The astronaut measures the time it takes a linear density of 7.9 10 kg/m. The astronaut measures the time it takes a transverse wave pulse to travel the length of the wire. The measured time was 0.064 s. Assume the mass of the wire is negligible compared to the mass of the ball, and calculate the acceleration due to gravity on this planet.
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16.5 Sound Waves Almost all of us can hear sounds, but what is a “ sound ”? Sound is a longitudinal (compression) wave that moves through a medium.
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This note was uploaded on 09/25/2011 for the course PHYS 2002 taught by Professor Blackmon during the Spring '08 term at LSU.

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Lecture_18 - 16.3 The Speed of a Wave Lets look at a...

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