## Periodic and Oscilatory Motions- Class 11 | Chapter – 14 | Physics Short Notes Series PDF for NEET & JEE

Periodic and Oscilatory Motions: Periodic motion refers to a motion that repeats itself in a regular cycle. This means that the motion returns to its starting position and velocity after a fixed time interval. Examples of periodic motion include the motion of a pendulum, the rotation of the earth around the sun, and the oscillation of a spring. On the other hand, oscillatory motion refers to a motion that repeats itself in a regular cycle around a central point or equilibrium position. Oscillatory motion can be periodic or non-periodic. Examples of oscillatory motion include the motion of a mass-spring system, the vibration of a guitar string, and the motion of a simple pendulum.

## Periodic and Oscilatory Motions

Periodic motion is a type of motion that repeats itself after a fixed interval of time. It is characterized by a repeating pattern of motion over time, and the time it takes for the pattern to repeat is called the period.

Periodic motion is found in many natural and man-made systems, including the motion of pendulums, the oscillations of a guitar string, the movement of ocean waves, and the alternating current in an electrical circuit.

In physics, the study of periodic motion is an important part of mechanics, and it is described mathematically using the concept of a wave function. This function describes the displacement of a point in space and time in response to a disturbance. The frequency of the periodic motion is defined as the number of cycles of the wave function per unit of time, and its wavelength is the distance between two consecutive points in the wave with the same phase.

Periodic motion is a fundamental concept in many areas of physics and engineering, as it plays a crucial role in the behavior of natural and man-made systems. Understanding the properties of periodic motion is important for designing and building machines and structures, as well as for understanding the behavior of natural phenomena such as sound, light, and the Earth’s climate.

### Types of Periodic Motion

There are several types of periodic motion, including:

• Simple Harmonic Motion (SHM): This is the most basic type of periodic motion and occurs when an object is subjected to a restoring force proportional to its displacement from an equilibrium position. Examples of simple harmonic motion include the motion of a mass on a spring and the pendulum of a clock.
• Circular Motion: This type of periodic motion occurs when an object moves in a circular path around a fixed center. Circular motion is found in many natural and man-made systems, such as the motion of the planets in the solar system and the rotation of wheels and gears.
• Rotational Motion: This type of periodic motion occurs when an object rotates about an axis. Rotational motion is found in many natural and man-made systems, such as the rotation of the Earth and the spinning of a wheel.
• Translational Motion: This type of periodic motion occurs when an object moves back and forth along a straight line. Translational motion is found in many natural and man-made systems, such as the motion of a piston in an engine and the movement of ocean waves.
• Combined Motion: This type of periodic motion occurs when an object experiences more than one type of periodic motion simultaneously. An example of combined motion is the motion of a spinning top, which experiences both rotational and translational motion.

Each type of periodic motion has its own unique characteristics and behaviors, and understanding these properties is important in many fields, including physics, engineering, and biology. For example, engineers use the principles of periodic motion to design machines and structures that can resist vibrations and minimize unwanted motion. In physics, the study of periodic motion is a fundamental part of mechanics and is used to explain the behavior of a wide range of physical systems.

### Important Formulae

Some Important Formulae of SHM

1. Displacement in SHM at any time is expressed as

y = a sin ωt

or y = a cos ωt

where a = amplitude and

ω = angular frequency.

1. Velocity of a particle in SHM is expressed as

v = ω √(a2 – y2)

At the mean position y = 0 and v is maximum. So, the maximum velocity is expressed as vmax = aω

At the extreme positions, displacement is the same as magnitude. So, y = a and v is zero.

1. Acceleration of a particle in SHM is expressed as

A or α = – ω2 y

A negative sign means the direction of acceleration is opposite to the direction in which displacement towards mean position.

At mean position y = 0 and acceleration is zero.

At extreme position acceleration is maximum. So, Amax = – aω2

1. Time period in SHM is expressed as

T = 2π √Displacement / Acceleration

## Oscillatory motion

Oscillatory motion is a type of motion characterized by repetitive back-and-forth or up-and-down movement. In an oscillatory system, an object moves away from a stable or equilibrium position, and then returns to that position after being subjected to a restoring force. The pattern of motion repeats over time, and the time it takes for one complete cycle is known as the period of the oscillation.

Oscillatory motion can be described by mathematical equations that describe the position, velocity, and acceleration of the object as a function of time. These equations are used to study the behavior of oscillatory systems and to predict their response to different types of inputs.

Oscillatory motion is found in many natural and man-made systems, including mechanical systems such as pendulums and springs, electrical systems such as oscillators and resonant circuits, and biological systems such as the beating of the heart and the motion of cells and tissues.

In physics and engineering, the study of oscillatory motion is an important part of mechanics and is used to understand the behavior of physical systems and to design machines and structures that can resist vibrations and minimize unwanted motion. For example, engineers use the principles of oscillatory motion to design shock absorbers for vehicles, which help to reduce the impact of bumps and vibrations on the passengers. In biology, the study of oscillatory motion is important for understanding the behavior of biological systems, such as the regulation of heart rate and the motion of cells and tissues.

### Types of Oscillatory Motion

There are several types of oscillatory motion, including:

• Simple Harmonic Motion (SHM):Simple harmonic motion (SHM) is a type of oscillatory motion specified for a particle travelling along a straight line with an acceleration that is proportional to the distance from a fixed point on the line.

A restoring force that obeys Hooke’s law has to restore any simple mechanical harmonic system (system of the weight hanged by the spring to the wall) that has been shifted from its equilibrium position. The mathematical expression of restoring force or Hooke’s law is as follows:

F = -kx

Where,

• F is the spring’s restoring elastic force in newton (N)
• is spring constant in Nm-1
• x is the displacement from equilibrium position in meter (m)

The negative sign in Hooke’s law describes the force as a restorative force that attempts to bring the spring back to its equilibrium position.

• Damped Oscillations: This type of oscillatory motion occurs when an external force or friction opposes the motion of an object, reducing the amplitude of its oscillations over time. Damped oscillations are found in many mechanical and electrical systems, such as a mass attached to a spring that is moving through a fluid.
• Forced Oscillations: This type of oscillatory motion occurs when an object is subjected to an external periodic force, causing it to oscillate at the frequency of the applied force. Forced oscillations are found in many mechanical and electrical systems, such as a mass attached to a spring that is being subjected to periodic impacts.
• Resonance: This type of oscillatory motion occurs when an object is subjected to a periodic force at its natural frequency, causing it to oscillate with a large amplitude. Resonance is found in many mechanical and electrical systems, such as a bridge that vibrates in response to the passage of a train.
• Nonlinear Oscillations: This type of oscillatory motion occurs when the restoring force is not proportional to the displacement from the equilibrium position. Nonlinear oscillations can result in more complex behavior, such as chaos and multi-stability, and are found in many natural and man-made systems, such as the motion of a pendulum with a large amplitude.

Each type of oscillatory motion has its own unique characteristics and behaviors, and understanding these properties is important in many fields, including physics, engineering, and biology. For example, engineers use the principles of oscillatory motion to design machines and structures that can resist vibrations and minimize unwanted motion, while biologists use these principles to understand the behavior of biological systems, such as the regulation of heart rate and the motion of cells and tissues.

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