 Periodic Motion

 periodic motion: are motions, which all repeat in a regular cycle  In each periodic motion, the object has one position at which the net force on it is zero. At that position, the object is in equilibrium.  Whenever the object is pulled away from its equilibrium position, the net force on the system becomes nonzero and pulls the object back toward equilibrium

Pendulums  Simple harmonic motion also can be demonstrated by the swing of a pendulum  A simple pendulum consists of a massive object, called the bob, suspended by a string or light rod of length l  The string or rod exerts a tension force, F T, and gravity exerts a force, F g, on the bob.  The vector sum of the two forces produces the net force, shown at three positions in the adjoining figure.

Resonance  It occurs when small forces are applied at regular intervals to a vibrating or oscillating object and the amplitude of the vibration increases.  The time interval between applications of the force is equal to the period of oscillation.

Waves  New Vocabulary  Wave Wave pulse Transverse wave  Surface wave Trough Crest  Wavelength Frequency Longitudinal wave  A wave is a disturbance that carries energy through matter or space.  Waves transfer energy without transferring matter

Type of waves according to need a medium to travel  1) Mechanical waves require a medium, such as water wave, air wave, ropes wave, or a spring. sound wave  2) Electromagnetic waves: waves not require medium. Light waves, TV waves, X-ray…..  A wave pulse is a single bump or disturbance that travels through a medium.

Types of waves according to pulse direction  1- A transverse wave is one that vibrates perpendicular to the direction of the wave’s motion Ex. Light waves, rope waves  2- longitudinal wave: The disturbance is in the same direction as, or parallel to, the direction of the wave’s motion  Sound waves are longitudinal waves. Fluids usually transmit only longitudinal waves.  3- a surface wave, which has characteristics of both transverse and longitudinal waves.  Waves that are deep in a lake or ocean are longitudinal; at the surface of the water, however, the particles move in a direction that is both parallel and perpendicular to the direction of wave motion, as shown in the figure below

Describing a wave  There are many ways to describe or measure a wave. Some characteristics depend on how the wave is produced, whereas others depend on the medium through which the wave travels.

1. Speed: how fast does wave move, depends only on the medium through which the waves move. 2. Amplitude: the maximum displacement of the wave from its position of rest or equilibrium  wave’s amplitude depends on how it is generated, but not on its speed.  Waves with greater amplitudes transfer more energy ( E α A 2 ) Describing a wave

 ( energy transferred α A 2 )  EX: Thus, doubling the amplitude of a wave increases the amount of energy it transfers each second by a factor of 4  ** trough : each low point of a wave  ** crest : Each high point of a wave Describing a wave

3. Wavelength ( λ ): The shortest distance between points where the wave pattern repeats itself  Depend on : a) frequency ( source) b) speed ( medium) 4. Phase: used to describe the position of a point in a wave  In phase: Any two points in wave separated by (λ, 2 λ, 3 λ,…..) OR ( 0, 2 π, 4 π,……)  Particles in the medium are said to be in phase with one another when they have the same displacement from equilibrium and the same velocity  Out of phase : Any two points in wave separated by (λ/2, 2 λ/2, 3 λ/2,…..) OR ( π, 3 π,5 π,……)  Particles in the medium with opposite displacements and velocities are out of phase Describing a wave

5. Period( T ) : time it takes the source to complete one cycle.  OR : Time taken by a point on wave to return to its initial phase 6. Frequency ( f ): number of complete oscillation( waves) in one second Describing a wave

1. Both the period and the frequency of a wave depend only on its source. They do not depend on the wave’s speed or the medium 2. period of wave = period of source Important Notes About Period And Frequency

 The wavelength of a wave is equal to the velocity divided by the frequency. Important Notes About Period And Frequency

 Q1: In fig1, if the total time is 0.2sec, find the wave length, period, frequency, speed, and amplitude.(#of waves is2.5  Q2: In fig1, find the period, frequency, and amplitude. If the wave length is 3m, what is the speed of the wave?

Q: Distinguish between transverse waves and longitudinal waves. 1.Transverse WaveLongitudinal Wave 1. A transverse wave is one that vibrates perpendicular to the direction of the wave’s motion. 2. A quick shake of a rope sends transverse waves in both directions. 3.Waves obtained in threads and ropes are transverse waves. 1. A longitudinal wave is one in which the particle displacement is in the same direction as, or parallel to, the direction of the wave’s motion. 2.The squeeze and release of a coiled-spring toy sends out longitudinal wave pulses in both directions. 3.Waves obtained in springs and sounds are longitudinal waves.