College of Science and Computer Science
Physical Sciences Department
TRANSVERSE AND LONGITUDINAL WAVES
A wave can be described as a disturbance that travels through a medium from one location to another location. In this experiment we used a slinky spring to demonstrate transverse and longitudinal waves. Longitudinal waves occur when the oscillations are parallel to the direction of propagation while Transverse waves occur when a disturbance creates oscillations perpendicular at right angles to the direction of energy transfer. To introduce a wave into the slinky, the first part of the spring is displaced or moved from its equilibrium or rest position. But once moved, it is returned to its original equilibrium or rest position. As we performed the up and down, and back and forth motion on the spring we would observe a repeating disturbance moving within the slinky that endures over a prolonged period of time referred to as a wave.
2. Actual Materials Used
- Helix / slinky spring
- Meter stick
3. Data and Results
Wave propagated – Up and Down motion – One and Steady
Type of wave: transverse
Wave propagated – Up and Down motion – Simultaneous motion
Type of wave: transverse
Wave propagated – Back and Forth motion
Type of wave: longitudinal
4. Interpretation of Data
In the experiment we have used a slinky wave as an example. When the slinky is stretched from end to end and is held at rest, it assumes a natural position known as the equilibrium or rest position. To introduce a wave here we must first create a disturbance. We must move a particle away from its rest position. One way to do this is to jerk the slinky forward to move it away from its equilibrium position and then back. The disturbance continues down the slinky. This disturbance that moves down the slinky is called a pulse. If we keep “pulsing” the slinky back and forth, we could get a repeating disturbance.
For the first two drawing the up and down motion you can see that we have created a transverse wave. In a transverse wave the pulse travels perpendicular to the disturbance. Comparing the simultaneous vs the one and steady motion the simultaneous motion created a bigger wavelength and amplitude than the one and steady motion. It is because a Constructive interference occurred, Constructive interference happens during a simultaneous motion whenever waves come together so that they are in phase with each other. This means that their oscillations at a given point are in the same direction, the resulting amplitude at that point is much larger than the amplitude of an individual wave. For the one and steady motion Destructive interference occurred, Destructive interference occurs when waves come together in such a way that they completely cancel each other out. When two waves interfere destructively, they must have the same amplitude in opposite directions. In this experiment we have found out that the particles do not move along with the wave; they simply oscillate up and down about their individual equilibrium positions as the wave passes by.
For the last drawing the back and forth motion you can see that we created a longitudinal wave. In a longitudinal wave the pulse is transferred through the medium of the slinky, but the slinky it does not actually move. It just displaces from its rest position and then returns to it. So what is being transferred in the slinky? It is the energy that is being transferred. The metal of the slinky is the just the medium that transfers the energy pulse of the wave. The medium ends up in the same place as it started it just gets disturbed and then returns to it rest position. In this experiment we have found out that the particles do not move down the tube with the wave; they simply oscillate back and forth about their individual equilibrium positions.
In conclusion a wave transports energy and not matter. When a wave is present in a medium the individual particles of the medium are only temporarily displaced from their rest position. There is always a force acting upon the particles that restores them to their original position. In a slinky wave, each coil of the slinky ultimately returns to its original position. Waves are said to transport energy. As a disturbance moves through a medium from one particle to its adjacent particle, energy is being transported from one end of the medium to the other. In this experiment we used a slinky wave, a person gives energy to the first coil by doing applying a force upon it in the experiment it’s either up and down or back and forth motion. The first coil in the spring receives a large amount of energy that it subsequently transfers to the second coil. When the first coil returns to its original position, it possesses the same amount of energy as it had before it was displaced. This process of energy transfer continues as each coil interacts with its neighbor. In this manner, energy is transported from one end of the slinky to the other, from its source to another location.
In a transverse wave energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced upwards and downwards. In this case, the particles of the medium move perpendicular to the direction that the pulse moves. While in a longitudinal wave energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced leftwards and rightwards. In this case, the particles of the medium move parallel to the direction that the pulse moves.
6. Guide Questions
- Define superposition of waves?
The principle of superposition is sometimes stated as follows: “When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location.”
The principle of superposition may be applied to waves whenever two (or more) waves travelling through the same medium at the same time. The waves pass through each other without being disturbed. For example two waves pass through each other without being disturbed, and the net displacement is the sum of the two individual displacements.
2. What happened to the waves when both ends of the spring are simultaneously moved up and down?
As both ends of the spring are simultaneously moved up and down it will create an interference. Interference is a phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude. There are 2 types of interference namely constructive and destructive interference.
When two waves come close to one another, their effects add together. If the crests, or highest parts of the waves, line up perfectly, the crest of the combined wave will be the sum of the heights of the two original crests. This is known as constructive interference, in which two waves (of the same wavelength) interact in such a way that they are aligned, leading to a new wave that is bigger than the original wave.
However, if two waves are not perfectly aligned, then when the crest of one wave comes along, it will be dragged down by the trough of the other wave. The resulting, combined wave will have crests that are shorter than the crests of either original wave, and troughs that are shallower than either of the incoming waves. This is known as destructive interference.
3. Define transverse waves. Give 3 examples.
For transverse waves the displacement of the medium is perpendicular to the direction of propagation of the wave. A ripple on a pond and a wave on a string are easily visualized transverse waves. Transverse waves cannot propagate in a gas or a liquid because there is no mechanism for driving motion perpendicular to the propagation of the wave.
- Surface waves are transverse waves.
- The visible light waves are transverse waves.
- Water wave is a transverse wave.
- Radio waves are also transverse waves.
- Television waves are transverse waves.
- Gamma rays are another example.
- The x rays are also electromagnetic as well as transverse in nature.
- The radio and microwave is example of transverse waves.
4. Define longitudinal waves. Give 3 examples.
In longitudinal waves the displacement of the medium is parallel to the propagation of the wave. A wave in a “slinky” is a good visualization. Sound waves in air are longitudinal waves.
- Sound wave
- Earthquake P wave
- Tsunami waves
- Waves in a slink
- Glass vibrations
- Internal water waves
- Ultra sound
- Spring oscillations
- Resnick and D. Halliday, Physics, Third Edition (John Wiley & Sons: New York, 1977).
- W. Sears, M. W. Zemansky and H. D. Young, University Physics, Sixth Edition (Addison-Wesley: Reading, Mass, 1981).
- Semat, Henry and Katz, Robert, “Physics, Chapter 20: Wave Motion” (1958). Robert Katz Publications. 162. http://digitalcommons.unl.edu/physicskatz/162