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# Periodic Motion

Periodic Motion . Periodic Motion. 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 .

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## Periodic Motion

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1. Periodic Motion Periodic Motion

2. 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

3. 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, FT, and gravity exerts a force, Fg, on the bob. • The vector sum of the two forces produces the net force, shown at three positions in the adjoining figure.

4. 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.

5. Waves • New Vocabulary • Wave Wave pulse Transverse wave • Surface wave Trough Crest • WavelengthFrequency Longitudinal wave • A waveis a disturbance that carries energy through matter or space. • Waves transfer energy without transferring matter

6. 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.

7. 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

8. 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.

9. Describing a wave • Speed: how fast does wave move, depends only on the medium through which the waves move. • 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 A2 )

10. Describing a wave • ( energy transferred α A2) • 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

11. Describing a wave • Wavelength ( λ ): The shortest distance between points where the wave pattern repeats itself • Depend on : a) frequency ( source) b) speed ( medium) • Phase: used to describe the position of a point in a wave • In phase: Any two points in wave separated by (λ, 2λ, 3λ,…..) OR ( 0, 2π, 4π,……) • 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, 2λ/2, 3λ/2,…..) OR ( π, 3π,5 π ,……) • Particles in the medium with opposite displacements and velocities are out of phase

12. Describing a wave • 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 • Frequency ( f ): number of complete oscillation( waves) in one second

13. Important Notes About Period And Frequency • 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 • period of wave = period of source

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

15. 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?

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