GRADE 7

MODULE 2, QUARTER 3; LESSON 2.1

Teacher’s Guide for Discussion

MA. RACHEL B. ESPINO

Teacher, Science

Buhatan NHS, Sorsogon City

• WAVES are perpendicular disturbance that moves away from a source and carries energy with it.

1. A wave is a travelling disturbance.

2. It carries energy from one phase to another.

3. Vibration causes wave motion

4. Waves travel through a medium

• According to the direction of movement of the individual particles of the medium relative to the direction that the waves travel.

• Waves in which particles of the medium move in a direction perpendicular to the direction that the wave moves.

• Particle motion is PERPENDICULAR to wave motion.

Example: waves made by rope.

• Waves in which particles of the medium move in a direction parallel to the direction that the wave moves.

• Particle motion is PARALLEL to wave motion.

Example: sound wave

• Waves in which the particles of the medium undergo a circular motion.

• In a surface wave, it is only the particles at the surface of the medium that undergo the circular motion. The motion of particles tend to decrease as one proceeds further from the surface.

• According to the waves’ ability to transmit energy through a vacuum (empty space)

• A wave that is capable of transmitting energy through a vacuum.

Example: rays of the sun, light

• Waves not capable to transmit energy through a vacuum.

Example: sound

• The high points of waves are called CRESTS or PEAKS while the low points are called TROUGHS.

• The AMPLITUDE is the maximum displacement from the rest position. It is the height of the crest or depth of a trough measured from the normal undisturbed position.

• The WAVELENGTH, λ is

the distance between

two successive crests

or two successive

troughs. It is also equal

to the distance between

any two identical

points on successive

waves.

• The FREQUENCY, f is the number of crests or troughs that pass a point per second. This is equivalent to the number of complete waves generated per second. Frequency is measured in terms of hertz (Hz).

• The PERIOD, T is the time taken to generate one complete wave. It is also the time taken for the crests or any given point on the wave to move a distance of one wavelength

T = 1/f

• The SPEED, v of the wave is the distance moved by a wave in one second. Since the wave crest travels a distance of one wavelength in one period, the wave speed;

v = λ/T or

v = f λ