Oscillation - A Level Physics

An object oscillates when it moves back and forth repeatedly, on either side of some equilibrium position.

If we stop the object from oscillating, it returns to the equilibrium position

If you pluck a guitar string, it continues to vibrate for some time after you have released it.

Every oscillator has a natural frequency with which it vibrates freely after an initial disturbance.

Free Oscillations

if you sit on a bus, you may notice that the vibrations from the engine are transmitted to your body causing you to vibrate with the same frequency.

these are not free vibrations of your body; they are forced vibrations.

​​Forced Oscillations

Amplitude, period, frequency, phase
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Amplitude, period and frequency

the shape of this graph is a sine curve, and the motion is described as sinusoidal.

The maximum displacement from the equilibrium position is called the amplitude x₀

The period T is the time for complete oscillation. Note that the oscillating object must go from one side to the other and back again (or the equivalent)

The frequency f is the number of oscillation per unit time.

Phase: the point that an oscillating particle has reached withen the complete cycle of an oscillation

Phase difference: the difference in the phases of two oscillating particles measured in degrees or radians

A body executes simple harmonic motion if its acceleration is directly proportional to its displacement from its equilibrium position, and in the opposite direction to its displacement

• a mass that oscillates

• a position where the mass is in equilibrium

• a restoring force that acts to return the mass to its equilibrium position

The greater the displacement x, the greater the acceleration a.

the minus sign shows that, when the object is displaced to the right, the direction of its acceleration is to the left.

​Equation for velocity

​a greater amplitude means that the oscillator has to travel a greater distance in the same time - hence it has a greater speed

Increasing the frequency means a shorter period. a given distance is covered in a shorter time - hence it has a greater speed

Energy Graph

an oscillation in which resistive forces causes the energy of the system to be transferred to the surroundings as internal energy

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Damped

Damping can be very useful if we want to get rid of vibrations.

damping is achieved by introducing the force of friction into a mechanical system. Damping has the effect of removing energy from the oscillating system.

a system oscillates with maximum amplitude by absorbing energy from a vibrating source. it occurs when the frequency of the driving force is equal to the natural frequency of the oscillating system.

​Millenium "Wobble" Bridge

​When 2000 people swayed in time with the bridge, it caused the amplitude of the bridge's oscillations to increase (become resonance).

​Damping is useful if we want to reduce the damaging effects of resonance.

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​An everyday example of damping can be seen on some doors

​critical damping is the minimum amount of damping required to return an oscillator to its equilibrium position without oscillating

​the particle of water in the food forced to vibrate and they absorbed the energy of microwave radiation.

​​Microwave

it uses the radiowaves that will be matched with the frequency of the organ's body.

​​MRI

​​Television