Difference Between Resonance and Natural Frequency

Resonance vs Natural Frequency

Resonance and natural frequency are two very important topics discussed under the topic waves and vibrations. It also plays a vital part in fields such as circuit theory, disaster management, engineering and even life sciences. This article will try to discuss these two phenomena, their significance, their similarities and finally their differences.

Natural Frequency

Every system has a property called the natural frequency. The natural frequency of a system is very important; it is the frequency the system will follow, if the system is provided with a small oscillation. Events such as earthquakes and winds can do destruction on objects with the same natural frequency as the event itself. It is very important to understand and measure the natural frequency of a system in order to protect it from such natural disasters. Natural frequency is directly related with resonance. It will be explained later. Systems such as buildings, electronic and electrical circuits, optical systems, sound systems and even biological systems have natural frequencies. They can be in the form of impedance, oscillation or superposition depending on the system.

Resonance

When a system (e.g: a pendulum) is given a small oscillation, it will start to swing. The frequency with which it swings is the natural frequency of the system. Now imagine a periodical external force applied to the system. The frequency of this external force doesn’t necessarily be similar to the natural frequency of the system. This force will try to oscillate the system to the frequency of the force. This creates an uneven pattern. Some energy from the external force is absorbed by the system. Now let us consider the case where the frequencies are same. In this case, the pendulum will freely swing with maximum energy absorbed from the external force. This is called resonance. In this case, even if the pendulum and the force were not at the same phase, the pendulum would eventually adapt to the phase of the force. This is a forced oscillation. Since the pendulum absorbs highest amount of energy at resonance, the amplitude of the pendulum is a maximum at resonance. This is the danger the earthquakes and storms bring. Suppose the natural frequency of a building is the same as that of the earthquake, the building will swing with the highest amplitude eventually collapsing. There is also a resonance state in LCR circuits. The impedance of any LCR combination depends on the frequency of the alternative current. The resonance takes place at the minimum impedance. The frequency corresponding to the minimum frequency is the resonance frequency. At the highest impedance, the system is said to be anti-resonant. This resonance and anti-resonance is widely used in tuning circuits and filter circuits respectively.