Sound waves

1. What is sound?

Sound is a form of energy propagated as waves that make our eardrums vibrate.
Sound waves are caused by vibrating objects.
Sound waves are longitudinal waves.

2. How is sound produced by a vibrating objects?

Sound waves are produced when a vibrating object causes the air molecules around it to vibrate.
When a tuning fork vibrates, layers of air vibrate and the sound energy is propagated through the air around it in the form of waves.
When the tuning fork moves forwards, the air is compressed.
When the tuning fork moves backwards, the air layers are pulled apart and cause a rarefaction.
Therefore, a series of compression and rarefactions will produce sound.



3.Why does sound waves is a longitudinal waves?

The air particles vibrate backward and forward in the direction parallel to the direction of propagation of the sound wave.

4. Explain how the loudness relates to amplitude

The loudness of the sound depends on its amplitude.
If the amplitude is increased, the loudness increases.

5. Explain how the pitch relates to frequency

A high pitch sound corresponds to a high frequency and a low pitch sound corresponds to a low frequency of vibration.

6.

The reflection of sound is called echoes.

i) Ultrasound waves (higher than 20 000 Hz) is used to scan and capture the image of a fetus in a mother’s womb.

ii) Sonar is the technique of using ultrasound to locate underwater objects or to measure the depth of a seabed.




Learn more :

http://en.wikipedia.org/wiki/Sonar
http://library.thinkquest.org/19537/Apps2.html
http://animals.howstuffworks.com/mammals/bat2.htm

Damping and resonance in an oscillating system

Damping and Resonance in an oscillating system


Damping simulation :
Click this link http://www.myphysicslab.com/spring1.html to find out effect of damping to energy, velocity and acceleration of the system.
set Y as position ( displacement of load), X as responding variables. Observe the pattern of the graph.


When damping occurs in an oscillating system, energy is lost to the surroundings, causing the amplitude of the oscillation to decrease.

When resonance occurs, the frequency of the forced vibration is equal to the natural frequency of the system. this causes the system to vibrate at maximum amplitude.

Virtual Lab in You-tube

1. Barton's Pendulum
2.Resonance


Quiz: Choose the correct answer.

1.
A system vibrates with a natural frequency. If a forced vibration of the same frequency is given to the system, what will happen ?

Tips : The forced vibration is the same as the natural frequency of the system .

a. Damping
b. Resonance
d. Natural frequency
d. Vibration

2. When does an oscillating system experience damping ?
a. when the amplitude of the oscillation decreases.
b. when the period decrease.
c. when the frequency increases.
d. when the amplitude remains constant.

3. Which of the following graphs shows greater damping effect?

Significant Figure

In measurement, significant figures relate the certainty of the measurement.
As the number of significant figures increases, the certainty of the measurement increase, which means we are more certain about what we have measured.
In the SPM syllabus, the magnitude of a physical quantity is usually rounded up to 3 or 4 significant figures.

Example:
speed of light in a vacuum = 299 792 458 ms ^-1

= 3.00 × 10⁸ ms^-1 (to 3 significant figures)

learn more form Form 4 Modern Mathematics .

Polish my skills:

Write your answer in 3 significant figures
1. The mass of insect is 0.006 g
2. The height of Petronas Twin Towers is 452 000 mm
3. The total area of Malaysia is 329750 km²

Standard form

It is impossible to do Physics without mathematics, therefore you need to polish your rusty mathematics skill .

Some physical quantities have extremely large magnitudes.
These extremely large and small values can be written in standard form ( scientific Notation ) so that it is neat, simple and easy to read.

Example :
a) Diameter of the earth is
= 130 000 000 metres
= 1.3 x 10⁷

b) Length of Paramyxoviruses
= 0.000014 m
= 1.4 x 10^-5


Polish my skills :

Write the following quantities in standard form :

a. The length of virus = 0.00 000 008 m
b. Red light wavelength = 0.00 000 067 m
c. the mass of a ship = 75 000 000 kg

1.1 Understanding Physics

In physics, we study natural phenomena and the properties of matter.
The aim of physics is to explain the fundamental nature of the universe by using the concept of physics.
Physics involves the conduct of studies and experiments to find answers to the question ‘Why?’and ‘How?’ in relation to the mysteries of the universe.
The majority of natural phenomena can be explained using the principles of physics, for example;
i) Shadows are formed because light travel in straight line.
ii) Black objects are black because almost all the light that falls on them is absorbed.

Fields of study in physics

1. Force and motion - investigates the action of force and motion.
2. Forces and pressure- pressure, pressure in liquids, gas pressure, atmospheric pressure, Pascal’s principle, Archimedes’ principle, Bernoulli’s principle.
3. Heat- Studies the influence of heat on different types of matter.
4. Light - explains the different phenomenon due to light.
5. Electricity and electromagnetism- investigates the interactions of electric and magnetic fields.
6. Electronics - studies the use of electronic devices in various field.
   
7. Waves - understands the properties of different types of waves and their uses.

I Know it :

The following diagrams show some of the natural phenomena and occurrences around us. Find out the related field of study in Physics.

1.

Car racing .
Field: _____________
2.

Cooking.
Field :______________

3.




Communication using mobile phone.
Field : ________________


4.

Shadows show ( Wayang Kulit )
Field: _________________

REFRACTION OF WAVES

Definition :

Refraction of waves is a change in its direction as the waves pass from one medium to another.
It occurs when there is a difference in the speed of the wave at the boundary of two mediums.

What happens after refraction of wave?
The wave has the same frequency, but a different speed, wavelength and direction of propagation.

example :
1.Water waves passes from deep water to shallow water
The wave has the same frequency, but speed decrease, wavelength decrease and the the water wave is refracted toward the normal.


2. Water waves passes from shallow water to deep water
The wave has the same frequency, but speed increase, wavelength increase and the the water wave is refracted away from the normal.

Refraction phenomena :
1. A swimming pool seems much shallower than it actually is.
2. The sound of a moving car at a distance is clearer at night than that in the day time. This is due to the effects of the refraction of sound waves.

Relationship between frequency, speed and wavelength .
v = f λ ( the wave frequency remain unchanged)
∴ v ∝ λ
f ₁ = f₂

v₁ = v₂
λ ₁ . λ ₂


Quiz :
1.
A plane wave has a wavelength of 2 cm and a velocity of 8 cm s^-1 as it moves over surface of shallow water. When the plane wave moves into an area of greater depth, its velocity becomes 12 cm s^-1. What is
(a) the wavelength
(b) the frequency
of the wave in the area of greater depth?