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Determine the value of the viscous damping coefficient \(c\) for which the system is critically damped. The cylinder mass is \(m=2 \mathrm{kg}\) and the spring constant is \(k=150 \mathrm{N} / \mathrm{m} .\) Neglect the mass and friction of the pulley.

Short Answer

Expert verified
The critical damping coefficient is approximately 34.64 Ns/m.

Step by step solution

01

Understand the Concept of Critical Damping

A critically damped system is one where the system returns to equilibrium as quickly as possible without oscillating. To achieve this, the damping coefficient \( c \) is set to a specific value that fulfills the critical damping condition.
02

Identify the Critical Damping Formula

The formula for the critical damping coefficient \( c_c \) in a mechanical system is given by \( c_c = 2\sqrt{km} \), where \( k \) is the spring constant and \( m \) is the mass of the system.
03

Substitute Known Values into the Formula

Substitute \( k = 150 \, \text{N/m} \) and \( m = 2 \, \text{kg} \) into the formula: \[ c_c = 2\sqrt{150 \times 2} \].
04

Calculate the Square Root

Calculate the product inside the square root: \( 150 \times 2 = 300 \), then find the square root: \( \sqrt{300} \).
05

Compute the Critical Damping Coefficient

Perform the final computation: \[ c_c = 2 \times \sqrt{300} \approx 2 \times 17.32 = 34.64 \, \text{Ns/m}. \]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Damping Coefficient
In mechanical systems, the damping coefficient is a parameter that influences how oscillations in the system decay over time. It essentially describes the degree of resistance you encounter when moving an object through a medium, like air or liquid. When a system experiences damping, it means some of the energy is lost, usually in the form of heat or sound. In the context of a critically damped system, the damping coefficient is specifically adjusted so that the system returns to its equilibrium state as quickly as possible without overshooting or oscillating back and forth.
  • Critical Damping: This occurs at a specific damping level where the system does not oscillate but returns to equilibrium swiftly.
  • Underdamping: When the damping is less than critical, allowing oscillations.
  • Overdamping: More than critical damping causes the system to return to equilibrium slowly without oscillation.
Given this, knowing how to calculate the critical damping coefficient, as demonstrated in the example with the formula \(c_c = 2\sqrt{km}\), allows you to intentionally control the damping properties to achieve desired mechanical responses.
Spring Constant
The spring constant, denoted as \(k\), is a measure of a spring's stiffness. It tells you how much force is needed to stretch or compress the spring by a unit distance. A high spring constant means a stiffer spring, which requires more force to deform. In our example, the spring constant is \(150 \, \text{N/m}\), meaning it takes 150 Newtons to stretch the spring one meter.Consider how this plays out in a damping scenario:- **Influence on Critical Damping:** A high spring constant increases the force returning a displaced object to its equilibrium, meaning more damping is needed to reach critical damping.- **Energy Storage:** Springs store potential energy. In dynamic systems, the spring constant helps determine how quickly this energy is moved back and forth as the system oscillates.Understanding the spring constant provides insight into how mechanical systems will respond under various forces and the requisite damping needed for efficient operation.
Mechanical System Dynamics
Mechanical system dynamics encompasses the behavior and interaction of masses, forces, springs, and dampers in a system. It involves understanding how these components work together to influence motion over time. These dynamics are crucial in designing systems that need to control or predict motion, like suspension systems in cars or earthquake-resistant buildings.**Key Elements in Mechanical Dynamics Include:**- **Mass \(m\):** Represents the inertia of the object. For a mass of \(2 \, \text{kg}\) from our example, this property resists changes in motion.- **Forces and Energy:** The interplay of kinetic and potential energy in the system determines the motion and stability.Understanding mechanical system dynamics assists engineers and designers in predicting how systems respond to various conditions. It allows for the optimization of systems such as damping configurations, which directly affect the time it takes for the system to settle and behave predictably in real-world applications.

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Most popular questions from this chapter

The instrument shown has a mass of \(43 \mathrm{kg}\) and is spring-mounted to the horizontal base. If the amplitude of vertical vibration of the base is \(0.10 \mathrm{mm}\) calculate the range of frequencies \(f_{n}\) of the base vibration which must be prohibited if the amplitude of vertical vibration of the instrument is not to exceed \(0.15 \mathrm{mm}\). Each of the four identical springs has a stiffness of \(7.2 \mathrm{kN} / \mathrm{m}\)

A single-cylinder four-stroke gasoline engine with a mass of \(90 \mathrm{kg}\) is mounted on four stiff spring pads, each with a stiffness of \(30\left(10^{3}\right) \mathrm{kN} / \mathrm{m},\) and is designed to run at 3600 rev/min. The mounting system is equipped with viscous dampers which have a large enough combined viscous damping coefficient \(c\) so that the system is critically damped when it is given a vertical displacement and then released while not running. When the engine is running, it fires every other revolution, causing a periodic vertical displacement modeled by \(1.2 \cos \omega t \mathrm{mm}\) with \(t\) in seconds. Determine the magnification factor \(M\) and the overall damping coefficient \(c\)

The seismic instrument shown is attached to a structure which has a horizontal harmonic vibration at \(3 \mathrm{Hz}\). The instrument has a mass \(m=0.5 \mathrm{kg},\) a spring stiffness \(k=20 \mathrm{N} / \mathrm{m},\) and a viscous damping coefficient \(c=3 \mathrm{N} \cdot \mathrm{s} / \mathrm{m} .\) If the maximum recorded value of \(x\) in its steady-state motion is \(X=2 \mathrm{mm}\) determine the amplitude \(b\) of the horizontal movement \(x_{B}\) of the structure.

In the equilibrium position, the 30 -kg cylinder causes a static deflection of \(50 \mathrm{mm}\) in the coiled spring. If the cylinder is depressed an additional \(25 \mathrm{mm}\) and released from rest, calculate the resulting natural frequency \(f_{n}\) of vertical vibration of the cylinder in cycles per second (Hz).

A linear oscillator with mass \(m\), spring constant \(k\) and viscous damping coefficient \(c\) is set into motion when released from a displaced position. Derive an expression for the energy loss \(Q\) during one complete cycle in terms of the amplitude \(x_{1}\) at the start of the cycle. (See Fig. \(8 / 7\).)

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