Unit 1 - Waves & Sound
Lesson 1: Vibrations
A wave is a transfer of energy taking the form of disturbance -- examples include sound waves,
light waves, seismic waves, etc. Waves are caused by vibrations, which are repetitive motions of
movement around equilibrium.
Types of Vibrations:
1. Transverse Vibrations → when an object vibrates perpendicular to the line of
equilibrium (up and down) i.e. a playground swing
2. Longitudinal Vibrations → when an object vibrates parallel to the line of equilibrium
(side to side) i.e. a spring
3. Torsional Vibrations → when an object twists around line of equilibrium (in circles) i.e. a
tetherball game
When describing the motion of a vibrating object, 1 complete oscillation is called a cycle (T),
measured in seconds. The number of cycles per second is frequency (f), measured in Hertz (Hz).
1 1
𝑓 = 𝑇
and 𝑇 = 𝑓
The term “in-phase” refers to when two vibrations have the same period & pass through
equilibrium at the same time.
In contrast, “out of phase” refers to when two vibrations have different periods or pass through
equilibrium at different times.
SUMMARY
❖ Most waves originate from a vibrating source/body
❖ Types of vibrations include transverse, longitudinal and torsional
❖ A wave is a transfer of energy in the form of disturbance
❖ Frequency (f, in Hz) is the number of cycles per second
❖ Period (T, in seconds) is the time required per each cycle
Lesson 1: Vibrations
A wave is a transfer of energy taking the form of disturbance -- examples include sound waves,
light waves, seismic waves, etc. Waves are caused by vibrations, which are repetitive motions of
movement around equilibrium.
Types of Vibrations:
1. Transverse Vibrations → when an object vibrates perpendicular to the line of
equilibrium (up and down) i.e. a playground swing
2. Longitudinal Vibrations → when an object vibrates parallel to the line of equilibrium
(side to side) i.e. a spring
3. Torsional Vibrations → when an object twists around line of equilibrium (in circles) i.e. a
tetherball game
When describing the motion of a vibrating object, 1 complete oscillation is called a cycle (T),
measured in seconds. The number of cycles per second is frequency (f), measured in Hertz (Hz).
1 1
𝑓 = 𝑇
and 𝑇 = 𝑓
The term “in-phase” refers to when two vibrations have the same period & pass through
equilibrium at the same time.
In contrast, “out of phase” refers to when two vibrations have different periods or pass through
equilibrium at different times.
SUMMARY
❖ Most waves originate from a vibrating source/body
❖ Types of vibrations include transverse, longitudinal and torsional
❖ A wave is a transfer of energy in the form of disturbance
❖ Frequency (f, in Hz) is the number of cycles per second
❖ Period (T, in seconds) is the time required per each cycle
