PARTS OF A WAVE AND ENERGY MOVEMENT

REVIEW Energy is required to make a wave. Waves are produced when a source of energy causes a vibration. A vibration is a repeated back-and-forth or up-and-down motion. When a vibration happens a wave results and information gets transferred.

REVIEW There are two kinds of waves, mechanical and electromagnetic.

REVIEW There are two types of waves, transverse waves which move up and down, and longitudinal waves which move back and forth or side to side.

REVIEW Mechanical waves are caused when moving energy causes a medium to begin to vibrate. Mechanical waves must have a medium, a solid, liquid, or gas to travel through. Mechanical waves can be longitudinal or transverse.

REVIEW Electromagnetic waves are caused when moving energy causes an electric charge to begin to vibrate. Electromagnetic charges do not need a medium to move, they can travel through anything, including the emptiness of space. Electromagnetic waves are always transverse waves.

REVIEW Waves are vibrations. Waves move energy and information. Two kinds of waves, electromagnetic and mechanical. Two types of waves, transverse and longitudinal. Longitudinal moves back and forth. Transverse moves up and down. Mechanical waves can be longitudinal or transverse. Electromagnetic waves are always transverse. Mechanical waves must move through a medium, a solid, liquid, or a gas. Electromagnetic waves can move through anything they don’t need a medium.

INTRODUCTION WAVE MOTION ENERGY MOVEMENT Energy and information transfer through transverse and longitudinal waves happens in two different ways. In a longitudinal wave, which moves, or oscillates, back and forth, the energy/information movement through the wave is parallel to the movement of the wave itself. Notice that as the energy/information moves through the wave, the particles of the medium are pushed with the wave, but move back to their original location after the energy has passed. ENERGY MOVEMENT

INTRODUCTION WAVE MOTION ENERGY MOVEMENT In a transverse wave, which moves, or oscillates, up and down, the energy/information movement through the wave is perpendicular to the movement of the wave itself. Notice that as the energy/information moves through the wave, the particles of the medium are moving up and down with the wave, but move back to their original location after the energy has passed. ENERGY MOVEMENT

INTRODUCTION In a transverse wave, some parts of the wave are very high while some parts are very low. The highest parts are called crests, or peaks, while the lowest parts are called troughs.

INTRODUCTION Transverse waves also have amplitude, how strong the wave is. In a transverse wave, amplitude is measured from the line which runs through the middle called the equilibrium or rest line, to the top of a crest or to the bottom of a trough.

INTRODUCTION The higher the waves go the greater the amplitude of the wave. You can think of the ripples on a pond for this type of amplitude. If you throw in a small pebble you get little ripples, small amplitude. If you throw in a large stone you get much larger ripples, greater amplitude.

INTRODUCTION The rest line which runs through the middle of the wave, is the point in which the wave would sit if there was no disturbance moving through it, which is sometimes also called the equilibrium position.

INTRODUCTION The last part of a transverse wave is its wavelength, literally how long it is. Waves can be as short as a few billionths of a meter to several million meters in length depending on the wave. Transverse wave are measured by the length of one complete cycle or repetition of the wave. Usually it is measured from the top of one crest to the top of the next crest, or from the bottom of one trough to the bottom of the next trough, but really it can be measured from any two adjacent points of the wave.

INTRODUCTION In a longitudinal wave some parts of the wave are close together, compressions, and some parts are spread apart, rarefactions.

INTRODUCTION Amplitude on a longitudinal wave is a measure of how compressed the particles of a wave become, or how rarefied the particles between compressions are. Basically, the thicker the compressions or the greater the distance between the compressions the greater the amplitude.

INTRODUCTION Think of a pair of tuning forks where one is struck lightly and the other is struck much harder. The one struck the hardest will vibrate more loudly than the one struck lightly, it will have a greater amplitude.

INTRODUCTION In a longitudinal wave the rest position of the wave would be like when a slinky is stretched out but none of it is moving. The coils are all the same distance apart. For this reason, when labeling the parts of a longitudinal wave, rest position or equilibrium is not labeled.

INTRODUCTION Wavelength in a longitudinal wave is measured from the center of one compression to the center of the next compression, or from the center of one rarefaction to the center of the next rarefaction.

INTRODUCTION Longitudinal lines and transverse waves have one other characteristic in common. If you compare them, the crests and troughs of a transverse wave match up with the compressions and rarefactions of a longitudinal wave. The crests are the compressions and the troughs are the rarefactions.

OBJECTIVES Label the parts of a transverse wave. Label the parts of a longitudinal wave. Determine the direction of particle motion in a wave.

VOCABULARY Transverse wave – wave in which the particles of the medium move up and down at right angles to the direction of the wave motion. Longitudinal wave – wave in which the particles of the medium move back and forth parallel to the direction of the wave motion.

IN QUESTION You are in a rowboat on a lake. A motorboat zooms by you. Describe what happens to you when the waves hit your boat.

ANSWER The boat moves up and down as the energy of the wave moves past the boat. The boat does not move in the direction of the energy. PARTICLE MOVEMENT ENERGY MOVEMENT

TRANSVERSE WAVE MOTION

NOTES Transverse waves move up and down. Particles move at right angles to the flow of energy. Particles do not travel with the energy.

Transverse Wave Motion – Label Figure 1 on your handout NOTES Transverse Wave Motion – Label Figure 1 on your handout

PARTS OF A TRANSVERSE WAVE

NOTES Transverse Wave Parts – Label Figure 2 on your handout wavelength crest amplitude rest line trough

NOTES Crest – high point of a transverse wave. Trough – low point of a transverse wave. Amplitude – measured from rest line to top of crest or rest line to bottom of trough. Wavelength measured from crest to crest of successive crests. Rest line – position where wave is not moving.

LONGITUDINAL WAVE MOTION

NOTES Longitudinal waves move back and forth. Particles move parallel to the flow of energy. Particles do not travel with the energy.

Longitudinal Wave Movement – Label Figure 3 on the handout NOTES Longitudinal Wave Movement – Label Figure 3 on the handout

PARTS OF A LONGITUDINAL WAVE

Longitudinal Wave – Label figure 4 on the handout NOTES Longitudinal Wave – Label figure 4 on the handout wavelength amplitude compression rarefaction

NOTES Compression – part of a longitudinal wave that is close together. Rarefaction – part of a longitudinal wave that is far apart. Amplitude measured as thickness of a compression or width of rarefactions. Wavelength measured from center to center of successive compressions, or center to center of successive rarefactions. Rest line – no rest position is shown.

OUT QUESTION Are ocean waves transverse waves or longitudinal waves? How do you know?

ANSWER Transverse - The water particles move up and down as the energy of the wave moves at a right angle to the particle direction. PARTICLE MOVEMENT ENERGY MOVEMENT