Where is damping used

On the other hand, the elastic potential energy of the trampoline's springs ensures that anyone of normal weight who jumps on the trampoline is liable to bounce some distance into the air. As a person's body comes down onto the trampoline fabric, this stretches the fabric itself highly elastic and, hence, the springs.

Pulled from a position of equilibrium, the springs acquire elastic potential energy, and this energy makes possible the upward bounce. As a car goes over a bump, the spring in its shock-absorber assembly is compressed, but the elastic potential energy of the spring immediately forces it back to a position of equilibrium, thus ensuring that the bump is not felt throughout the entire vehicle. However, springs alone would make for a bouncy ride; hence, a modern vehicle also has shock absorbers.

The shock absorber, a cylinder in which a piston pushes down on a quantity of oil, acts as a damper—that is, an inhibitor of the springs' oscillation.

Simple harmonic motion occurs when a particle or object moves back and forth within a stable equilibrium position under the influence of a restoring force proportional to its displacement. In an ideal situation, where friction played no part, an object would continue to oscillate indefinitely. Of course, objects in the real world do not experience perpetual oscillation; instead, most oscillating particles are subject to damping, or the dissipation of energy, primarily as a result of friction.

In the earlier illustration of the spring suspended from a ceiling, if the string is pulled to a position of maximum displacement and then released, it will, of course, behave dramatically at first. Over time, however, its movements will become slower and slower, because of the damping effect of frictional forces.

When the spring is first released, most likely it will fly upward with so much kinetic energy that it will, quite literally, bounce off the ceiling. But with each transit within the position of equilibrium, the friction produced by contact between the metal spring and the air, and by contact between molecules within the spring itself, will gradually reduce the energy that gives it movement. In time, it will come to a stop. If the damping effect is small, the amplitude will gradually decrease, as the object continues to oscillate, until eventually oscillation ceases.

On the other hand, the object may be "overdamped," such that it completes only a few cycles before ceasing to oscillate altogether. In the spring illustration, overdamping would occur if one were to grab the spring on a downward cycle, then slowly let it go, such that it no longer bounced. There is a type of damping less forceful than overdamping, but not so gradual as the slow dissipation of energy due to frictional forces alone.

This is called critical damping. In a critically damped oscillator, the oscillating material is made to return to equilibrium as quickly as possible without oscillating. An example of a critically damped oscillator is the shock-absorber assembly described earlier. Even without its shock absorbers, the springs in a car would be subject to some degree of damping that would eventually bring a halt to their oscillation; but because this damping is of a very gradual nature, their tendency is to continue oscillating more or less evenly.

Over time, of course, the friction in the springs would wear down their energy and bring an end to their oscillation, but by then, the car would most likely have hit another bump. Therefore, it makes sense to apply critical damping to the oscillation of the springs by using shock absorbers. Many objects in daily life oscillate in a spring-like way, yet people do not commonly associate them with springs.

If the mass is disturbed from the equilibrium position by a brief external force, it will have a natural frequency of f0. The range of this vibration disappears over time based on the spring damping function, described as the mechanical loss factor.

Due to its closed, cellular structure, filled with air, cork has a higher loss factor than rubber, which is essential for damping and consequent energy dissipation. The Acousticork Vibration Isolation range from Amorim Cork Composites offers solutions with an excellent compromise between damping and insulation. Construction E-book Vibration Isolation Acousticork Damping is a way to limit vibrations and is essential for protecting the system as a whole.

With less-than critical damping, the system will return to equilibrium faster but will overshoot and cross over one or more times. Such a system is underdamped ; its displacement is represented by the curve in Figure 2. Curve B in Figure 3 represents an overdamped system. As with critical damping, it too may overshoot the equilibrium position, but will reach equilibrium over a longer period of time. Figure 3. Displacement versus time for a critically damped harmonic oscillator A and an overdamped harmonic oscillator B.

Critical damping is often desired, because such a system returns to equilibrium rapidly and remains at equilibrium as well. In addition, a constant force applied to a critically damped system moves the system to a new equilibrium position in the shortest time possible without overshooting or oscillating about the new position.

For example, when you stand on bathroom scales that have a needle gauge, the needle moves to its equilibrium position without oscillating.

It would be quite inconvenient if the needle oscillated about the new equilibrium position for a long time before settling. Damping forces can vary greatly in character. Friction, for example, is sometimes independent of velocity as assumed in most places in this text. But many damping forces depend on velocity—sometimes in complex ways, sometimes simply being proportional to velocity.

Damping oscillatory motion is important in many systems, and the ability to control the damping is even more so. This is generally attained using non-conservative forces such as the friction between surfaces, and viscosity for objects moving through fluids.

The following example considers friction. Suppose a 0. Figure 4. The transformation of energy in simple harmonic motion is illustrated for an object attached to a spring on a frictionless surface. When there is damping, amplitude decrease and period increase.

Types of Damping 1. Light damping Defined oscillations are observed, but the amplitude of oscillation is reduced gradually with time. Light Damping 2. Critical Damping The system returns to its equilibrium position in the shortest possible time without any oscillation. Critical and heavy damping 3. Heavy Damping The system returns to the equilibrium position very slowly, without any oscillation.

Heavy damping occurs when the resistive forces exceed those of critical damping.