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

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