Grade 7 lesson about the nature of waves

1. Nature of Waves
By: Victor R. Oribe

2. A Vibration is a repeated back and
forth motion or oscillation of an
object.

3. Any elastic solid can be made to
vibrate.
Amplitude is the maximum
displacement an elastic
object can make.
When the load is released,
it vibrate back and forth.
If the surface is frictionless, then the magnitude of the
maximum displacement to the right and to the left of the
equilibrium position are equal

4. The motion of the load repeats itself over and over on a
definite path in equal intervals of time.
The periodic vibration of the mass is called Simple
Harmonic Motion (SMH).
SMH is a type of vibration along a path in which the
displacement of the object from its equilibrium position is
always equal above and below its equilibrium position

5. A simple pendulum oscillates back and forth.
If the pendulum bob moves from A
to C then back to A, it has one
complete vibration.
The time it takes the pendulum bob
to complete one vibration is called
the Period or T.
The number of complete vibration
in a second is the Frequency or f.

7. Assignment:
1. In your own words, explain the following:
1. vibration
2. elastic object
3. period
4. frequency
5. amplitude
6. simple harmonic motion
7. equilibrium position
2. Explain how waves are produced.

8. Vibrating objects act as sources of different forms of
waves.
Vibrating
Radio waves
electrons
Earthquake beneath Radio waves
the ocean

9. Electromagnetic Waves
Waves that need no medium to travel in.
James Clerk Maxwell a Scottish physicist predicted the
existence of electromagnetic waves in 1865.
Maxwell found out that these waves are produced by
oscillating charges.
Examples of these waves are:
a. light waves
b. radio waves
c. microwaves
d. X-rays

10. Mechanical Waves
Waves that need materials medium through which they
can travel.
Some examples of mechanical waves are sound waves
and water waves, or a waves that travel along a spring or
rope.

11. For the waves in a string, the particles oscillates up and
down while the waves move horizontally.
The direction of motion of the particles of the medium
(string) is perpendicular to the direction of the
waves, these waves are called Transverse Waves.

12. When the end of the spring is pushed and pulled,
a series of compressions and expansions occur.
compressions
expansions

13. Compressions and expansions are equivalent to the crest
and troughs of a transverse wave.
compressions expansions

14. Waves in Different Media
Transverse waves travel through a medium whose
particles are attached to one another.
Gas particles are widely separated making transverse
waves unable to travel through them.
A longitudinal waves causes particles of a gas to move
closer together or farther apart, making gas a medium
for it.
Both transverse wave and longitudinal waves can travel
through a solid since the particles of solid can vibrate
about their relatively fixed positions in any directions.

15. Guide Questions:
1. Differentiate electromagnetic waves from Mechanical
waves.
2. What are the different types of mechanical waves?
3. Compare and contrast longitudinal and transverse
wave in terms of:
a. direction of oscillation of the particles
b. direction of motion of the waves
c. medium through which they can travel

16. Wave Characteristics

17. Crest is the high points on a wave.
Troughs is the low points on wave.
Amplitude is the distance of the
crest or trough from the midpoint
of the waves.
Wavelength is the distance from
crest to crest or trough to trough

18. Frequency (f) refers to the number of crests or waves
that pass a fixed point per second measured in hertz
(Hz)

19. Set work
Identify the different part (characteristics) of waves.

20. Assignment
1. Give at least five examples on how energy
is transmitted by waves.
2. Give at least five reasons how energy is
transmitted by waves.

21. Research Work
1. Make a research on how microwave oven
operates.
2. Is it safe to use microwaves oven?

22. Short Quiz
1. Answer the chapter quiz (Chapter 16).
2. Copy and answer.