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61 terms

Waves-7th grade science

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wave
a disturbance that transfers energy from place to place
What can act as a medium?
solids, liquids, gases
mechanical waves
waves that require a medium to travel
When waves travel through a medium, what happens to the medium?
The waves do not carry the medium with them
What happens to the motion of a duck on a pond when a wave passes under it
The duck bobs up and down but does not move along with the wave
medium
the material through which a wave travels
Give an example of a wave that can travel through empty space
sunlight (electromagnetic waves)
how are mechanical waves produced?
when a source of energy causes a medium to vibrate
vibration
a repeated back and forth or up and down motion
how are mechanical waves classified?
by how they move
transverse waves
waves that move the medium at right angles to the direction in which the waves travel
Suppose you move the free end of a rope up and down to make a wave. In that case the rope is the medium. What is the relationship between the movement of the wave and the movement of the particles of the medium?
the wave moves along the length of the rope while the medium's particles move at right angles to the direction of the wave.
crest
the highest part of a transverse wave
trough
the lowest part of a transverse wave
longitudinal waves
waves that move the particles of the medium parallel to the direction in which the waves are traveling
compressions
the part in a longitudinal wave where the coils are close together
rarefractions
the parts in a longitudinal wave where the coils are spread out.
two types of waves:
transverse and longitudinal. Transverse waves have crests and troughs. Longitudinal waves have compressions and rarefractions
If you were to draw a longitudinal wave, you should think of compressions like they are
the crests on a transverse wave
If you were to draw a longitudinal wave, you should think of rarefractions like they are
the troughs on a transverse wave
4 properties of waves
amplitude, wavelength, frequency, speed
amplitude
the maximum distance the particles of the medium carrying a wave move away from their rest position
the amplitude of a water wave
the maximum distance a water molecule moves above or below the surface of calm water
the amplitude of a wave is
a direct measure of its energy
the amplitude of a LONGITUDINAL wave
a measure of how compressed and rarefied the medium becomes
the amplitude of a TRANSVERSE wave
the distance from the rest position to a crest or trough; the maximum distance the particles move up or down from their rest position
If a longitudinal wave has crowded compressions and loose rarefractions, what is the size of its amplitude?
large
wavelength
the distance between two corresponding parts of a wave
how can you find the wavelength of a transverse wave
Measure the distance from crest to crest or from trough to trough
How can you find the wavelength of a longitudinal wave
measure the distance between compressions
frequency
the number of complete waves that pass a given point in a certain amount of time
1 Hz (hertz)
1 wave per second
Hertz
the unit used to measure frequency
speed
how far the wave travels in one unit of time
speed
wavelength times frequency
frequency
speed divided by wavelength
wavelength
speed divided by frequency
when is the speed of a wave constant?
in a given medium under the same conditions
when will the speed of sound waves traveling through the air change
if the temperature and pressure of the air changes
what happens to the speed of a wave if you change to a different medium?
the wave may travel at a different speed
if you increase the frequency of a wave,
the wavelength must decrease
refraction
Wave enters a new medium at an angle. One side of the wave changes speed before the other side causing the wave to bend
reflection
the bouncing back of a wave when it hits a surface through which it cannot pass
diffraction
when a wave moves around a barrier or through an opening in a barrier it bends and spreads out
interference
the interaction between waves when they meet
constructive interference
adds the two waves' energies
destructive interference
subtracts the two waves' energies
standing wave
a wave that appears to stand in one place. It is really two waves interfering as they pass through each other.
law of reflection
the angle of incidence equals the angle of reflection. All waves obey this law
angle of incidence
The angle between the incoming wave and the perpendicular line
angle of reflection
the angle the reflected ray makes with the perpendicular line
refraction
the bending of waves as they enter a different medium
When does bending occur?
ONLY when the wave enters the new medium at an ANGLE
why does the bending of a wave entering a new medium occur?
because the two sides of the wave are traveling at different SPEEDS
when does constructive interference occur?
When waves combine their crests or troughs to produce a wave with larger amplitude
what happens when the crests of two waves overlap?
They combine their amplitudes to produce a wave with larger amplitude. The crests become higher.
What happens when destructive interference occurs between waves with different amplitudes?
The wave whose amplitude is greater will remain minus the amplitude of a lesser wave. The amplitude of the resulting wave will be smaller.
node
a point of zero amplitude on a standing wave
antinodes
the points of maximum amplitude on a standing wave
frequency of vibration
most objects have a natural frequency of vibration
Resonance
when external vibrations match an object's natural frequency