CBSE Class 11 Physics Notes Chapter 14 Oscillations

What are Oscillations?

Oscillation is a measure of some repetitive variation, as a function of time. It can be measured with respect to a state of equilibrium. The most common and simplest example for oscillation is the motion of a simple pendulum.

What are the three main types of Simple Harmonic Motion?

The three main types of simple harmonic motion in physics are:

  • Free Oscillation
  • Forced Oscillation
  • Damped Oscillations

Free Oscillation

In here, the amplitude and time period remains constant without any influence of external factors. When the system has zero damping, the amplitude remains constant provided, this theory is possible in cases where damping always occurs.

In order to overcome external forces like air resistance or friction, the reduction in amplitude(energy loss of a system) is referred to as damping. As a result, the amplitude, frequency, and energy all remain constant.

Forced Oscillation

When an external periodic force influences a body’s oscillation, then it is called forced oscillation. Here, damping occurs in the amplitude of oscillation but remains constant with the help of the external energy supplied by the system.

For example, constantly pushing a swing so that its oscillation doesn’t reduce.

Damped Oscillation

The reduction of the amplitude of an object with respect to time, such type of oscillations are known as damped oscillations. The energy of a system decreases with the decrease in amplitude. There are two types of damping:

  • Natural Damping
  • Artificial Damping

Important Questions

  1. Which of the following examples represent periodic motion?
    • (a)The return trip of a swimmer when he is completing one trip from the bank of a river to the other
    • (b)The release of a freely hanging bar magnet which has been displaced in N-S direction
    • (c)Rotating a hydrogen molecule about its mass’s center
    • (d)The release of an arrow from a bow
  1. Which of the following examples represent (nearly) simple harmonic motion and which represent periodic but not simple harmonic motion?
    • (a)Earth’s rotation on its axis
    • (b)In U-tube, the oscillating motion of the mercury column
    • (c)When a smoothly curved ball is released from the point which is above the lowermost point, the motion of the ball bearing inside of the ball
    • (d)In a polyatomic molecule, the general vibrations about its equilibrium

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Practise This Question

A train is travelling at the speed of 180 km/hr. In order to trap superman Lex Luthor has broken the tracks. Unware of Luthor's evil intensions, superman tries to stop the train by pushing it in opposite direction.Right at the moment when the train is 300 m away from the crack in the track, Superman is applying a deceleration of 5 m/s2. Just after 2 sec a bullet laced with kryptonite hits superman which incapacitates him for a while. How long has super man got to remove the bullet and start to give deceleration so to protect the innocents? (Trains brake system has failed)