3.1
- Compare the reactions and the different types of waves when the variables that affect them, change. Record the observations.
4th Part:
- One person grabs the heavy spring on one end, and another person grabs it by the other.
- Place the spring on the ground, and with the ruler measure 33 cm amplitude.
- Place an object that will be easy to tip over by a little tap, whether it is a ruler placed in a vertical position or a pen placed in a vertical position, 66cm away from the spring, but just in the middle of it. (See picture 4.1)
- Both persons at the ends will start at the same time two waves by making the same whip like movement of 33 cm in amplitude.
- Observe how the waves go and meet, what happens to the object placed at the side of the spring? How do the waves react after having met?
- Record observations.
4.1
5th Part:
- One person grabs the heavy spring on one end, and another person grabs it by the other.
- Place the spring on the ground, and with the ruler measure 33 cm amplitude.
- Place an object that will be easy to tip over by a little tap, whether it is a ruler placed in a vertical position or a pen placed in a vertical position, 66cm away from the spring, but just in the middle of it.
- Both persons at the ends will start at the same time two waves by making the same whip like movement of 33 cm in amplitude, with the difference that one person will make the wave start on the bottom side of the spring and the other will make it start on the upper side, hence creating two waves of equal amplitudes but moving in different directions and through different sides of the spring. (See picture 5.1)
- Observe how the waves go and meet, what happens to the object placed at the side of the spring? How do the waves react after having met?
- Record observations.
5.1
6th Part:
- One person grabs the heavy spring on one end, and another person grabs it by the other.
- Having the spring hanging on the air, one of the persons will move his hand up and down, with a constant amplitude and velocity.
- Record the behavior of the wave produced.
- Increase and Decrease the amplitudes, as well as the velocities, to change the shape of the spring.
- Record the shape variations, and compare.
Observations:
- Part 1:
- The wave moves along the upper part of the spring, until it reaches the other end, then it returns in the opposite direction and through the lower side.
- The returning wave is a reflection of the going wave.
- Part 2:
- The wave moved along the upper part of the spring, and when it came back, it also came through the upper part of the wave.
- It looked as if it had bounced.
- Part 3:
- Part 4:
- Both waves crash and make a bigger wave that tips the ruler, and then they continue their path. Because the interfering waves have displacement at the same direction, when they interfere, they add up, making the wave higher. This is an example of how two pulses, who act on the same side of the spring, at the same place and time, the displacement of the spring is the sum of both pulses.
- Part 5:
- Both waves seem to cancel each other at the point where they meet, hence they don’t trip the ruler; then they keep on with their regular path. This is an example of how two similar pulses, acting on different sides of the spring, at the same place and time, cancel each other.
- Part 6:
- That the waves seem to be moving around an axis, without moving back and forth, they stay in one place.
-
As the velocity of the “whip” increases, the more static waves are created, passing from the fundamental frequency, 1st harmonic, to the 2nd harmonic, 3rd harmonic and so on.
Causes of Error:
- Friction of floor and air affect the results.
- Measurements have a degree of uncertainty
- When generating waves, the amplitude needed is not matched, or is exceeded.
- Time taking was not accurate
Conclusions
When through a spring passes a longitudinal wave, each individual point moves parallel to the medium, left and right, as shown in diagram 1. Longitudinal waves consist of compressions and rarefactions. A compression is where the coils of the spring come together, and rarefaction is where the coils of the spring are pulled apart. An example of this kind of waves is sound and P waves in earthquakes.
When through a spring passes a transverse wave, each individual point moves perpendicular to the medium, as shown in Diagram 2. In this kind of waves, the maximum positive displacement from the equilibrium point, or the medium, is called the crest, while the maximum negative displacement is called the trough. An example of this kind of wave is light.
The speed of the pulse, in an ideal situation, does not change as it moves along the spring, but because of friction and other interference, it gradually stops. Based on the formula v= Fλ, we can conclude that overall, there is only one velocity.
When changing the amplitude of the pulses, the time needed for a pulse to go back and forth changed very little, almost nothing, so we can conclude that the amplitude of the pulses don’t affect significantly the velocities of the pulse. When the tension of the slinky was increased, the time it took for a pulse to go back and forth decreased, and therefore the velocity increased. When the medium was changed, the velocity was clearly affected. It is clear that changes in the medium do affect the speed.
For complete destruction interference, what must be truth is that the pulses are on opposite sides of the spring, that they have the same frequency and magnitude. The standing wave interference pattern are produced as the result of the repeated interference of two waves of identical frequency while moving in opposite directions along the same medium. In this patters, the wave length is from node to node. It is easier to measure the wavelength using this pattern than to measure it directly because of the constant interference and movement of the waves, making it simpler to determine the wavelength by just measuring from node to node. When the frequency of the pulses in this pattern is increased, more waves would be created, and so there would be more nodes, more interference, coming to a point where the interference would be so high and constant, that it would seem as if they would be no waves. In the diagrams below, we can see the how in certain time periods, the waves would interfere destructively and cancel the waves, and while sometimes they act constructively, making the waves increase.
Bibliography
Slinky Booklet. NASA. 3 Mar. 2004
<http://swift.sonoma.edu/education/slinky_booklet/>.
Henderson, Tom. Interference of Waves. 2001. The Physics Classroom. 3 March.
2004 <>
GCSE Physics. Gcsescience.com. 3 March 2004.
2004 The Physics Classroom and Mathsoft Engineering & Education, Inc. 3 March 2004