Making Sound Wave

How do vibrating objects make sound waves?
When you hit the drumhead it starts vibrating up and down. As the drumhead moves upward, the molecules next to it are pushed closer together. This group of molecules that are closer together is a compression.

When the drumhead moves downward, the molecules near it
have more room and can spread farther apart. This group of molecules
that are farther apart is a rarefaction. The rarefaction also
moves away from the drumhead.As the drumhead vibrates up and
down, it forms a series of compressions and rarefactions that move
away and spread out in all directions. This series of compressions
and rarefactions is a sound wave.

Wave

What is a wave?
• Waves transfer energy, but do not transfer
matter.

Mechanical Waves
• Mechanical waves require a medium in which
to travel.
• When a transverse wave travels, particles of
the medium move at right angles to the direction
the wave is traveling.
• When a compressional wave travels, particles
of the medium move back and forth along the
same direction the wave is traveling.
• Sound is a compressional wave.

Electromagnetic Waves
• Electromagnetic waves can travel through
empty space.
• The Sun emits different types of electromagnetic
waves, including infrared, visible light,
and ultraviolet waves.

What is DENSITY ?

DENSITY is a physical property of matter, as each element and compound has a unique density associated with it. Density defined in a qualitative manner as the measure of the relative "heaviness" of objects with a constant volume.

For example: A rock is obviously more dense than a crumpled piece of paper of the same size.
A Styrofoam cup is less dense than a ceramic cup.

Density may also refer to how closely "packed" or "crowded" the material appears to be - again refer to the Styrofoam vs. ceramic cup.

The formal definition of density is mass per unit volume. Usually the density is expressed in grams per mL or cc. Mathematically a "per" statement is translated as a division. cc is a cubic centimeter and is equal to a mL Therefore,




Where:
m = mass (kg)
V = Volume (m3)
ρ = Density (kg/cm3)


Example: Calculate the density in g/mL of aluminum if a 50 mL block weighs 135 g.

Solution:
Apply the definition:


Density = 135 : 2,70 = 50 g/mL