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Transverse & Reflected Pulses. Created for CVCA Physics By Dick Heckathorn 03 May 2K + 5. 02 Transmitted and Reflected Pulses. 16 Pulses on a “Frictionless” Slinky. 28 Reflection and Refraction. Generate a pulse by giving the slinky a flick at right angles to the length of the slinky. .
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Transverse & Reflected Pulses Created for CVCA Physics By Dick Heckathorn 03 May 2K + 5
02 Transmitted and Reflected Pulses 16Pulses on a “Frictionless” Slinky 28 Reflection and Refraction
Generate a pulse by giving the slinky a flick at right angles to the length of the slinky. How does one describe the shape of the pulse? Length Height (Amplitude) How can one change the length of the pulse? By changing how fast one creates the pulse. How can one change the amplitude of the pulse? By changing how far one moves the hand to right or left.
Figure 1 The generation and motion of a pulse along a spring shown by a series of pictures taken with a movie camera.
How fast do the pulses travel? • What did you measure? • distance time What distance? What time? You choose the time it takes to go the chosen distance.
How can one change the speed of the wave? • By changing the length of the stretched spring. • (By changing the tension on the slinky.)
Figure 2 • What does a specific point on a slinky do as a pulse goes by?
What is happening to the shape of the leading half of the pulse? • To the trailing half of the pulse?
Make a pulse. • Observe its propagation and then make a sketch of the pulse at one instant of time. • Then make a sketch of the pulse a very, very short time later.
Has the shape of the pulse changed as it moves along the slinky? • Length? Amplitude? • Why? • There is friction between the slinky and the floor which removes energy from the pulse.
What would change if the slinky were suspended so that it didn't touch the floor? • Less friction, less change in amplitude • What if it was suspended in water? • More friction
Figure 6 • What happened to the pulse when it arrives at the far end? It reflected and came back on the opposite side.
Figure 9 • What happened to the reflected pulse when it reflected from the string end of the slinky? • It reflected back on the same side of the slinky that the original pulse was generated.
Pulses on a “Frictionless” Slinky • For this part of the experimentation, you will be watching two people investigate pulse phenomena on a slinky with very little friction.
What happens to the pulse as it reflects from a held end? • It reflects back on the opposite side with very little amplitude change. • This is due to the absence of friction between slinky and floor.
2. Determine the speed of the pulse by first finding the time for the wave to travel from one end to the other and back to the original end.
When the slinky is stretched to a greater length, how does the time it takes the pulse from one end to the other and return compare to the previous measurement? • It is the same. • How does the speed compare? • I trust that you did not say the same.
4. What property(s) of a slinky changed as it was stretched? • tension mass per length • The following equation shows how the tension and mass per unit length affects the speed.
What happens to the pulse as it reflects from an end held by a long string? • It reflected back on the same side of the slinky that the original pulse was generated.
Figure 5 • What is observed when two similar pulses (same amplitude) are sent down the slinky, one from each end, oriented in the same direction, at the same time.
Figure 5 What do you see in segment F? Do you see the absence of blur? What does this indicate? It indicates there is no motion of the pulse at that instant.
Figure 3 • When pulses are generated from each end, do they pass through or reflect back from each other? They pass through each other.
Set a pop can half way from both ends and a distance away from the slinky of between 1 and 2 amplitudes of the pulse. • Send one pulse from each end with the orientation in the same direction. • Describe what happens to the pop can. Explain why.
With the pop can in the same position, send one pulse from each end with the orientations in opposite directions. • Describe the result.
Figure 4 The superposition of two equal and opposite pulses on a coil spring. In the fifth picture they almost cancel each other.
Less Into More Dense Material • When a pulse is sent from the end of a slinky, what is observed? Figure 8 The transmitted pulse is upright. The reflected pulse is upside down.
What did we observe when a metal and a plastic slinky were connected together?
Plastic Into Metal Slinky • When a pulse is sent from the plastic end of a slinky connected to a metal slinky, what is observed? • The transmitted pulse in the metal slinky is upright. • The reflected pulse in the plastic slinky is upside down.
More Into Less Dense Material • When a pulse is sent from the metal end of a slinky, what is observed? Figure 7 The transmitted pulse is upright. The reflected pulse is upside down.
Metal Into Plastic Slinky • When a pulse is sent from the metal end of a slinky connected to a plastic slinky, what is observed? • The transmitted pulse in the plastic slinky is upright. • The reflected pulse in the metal slinky is upright.
Figure 2 The motion of a pulse from right to left along a spring with a ribbon around one point. The ribbon moves up and down as the pulse goes by but does not move in the direction of motion of the pulse.
