ODE application of damped motion

In summary, a mass of 40 g stretches a spring 10 cm, and a damping device with a resistance equal to 560 dynes/(cm/s) times the instantaneous velocity is involved. To find the equation of motion, the units do not have to be converted to CGS, but if desired, the resistance should be converted to 56000 N/(m/s).
  • #1
leroyjenkens
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Homework Statement


A mass of 40 g stretches a spring 10 cm. A damping device imparts a resistance to motion numerically equal to 560 (measured in dynes/(cm/s)) times the instantaneous velocity. Find the equation of motion if the mass is released from the equilibrium position with a downward velocity of 2 cm/s.


Homework Equations



[itex]\frac{d^2x}{dt^2}+\frac{β}{m}\frac{dx}{dt}+\frac{k}{m}x=0[/itex]

The Attempt at a Solution


The only thing I think that's stopping me from doing this problem is the units. I converted 40g to .04 kg, and 10 cm to 0.1 m. But I'm not sure what to do with the 560 dynes/(cm/s). Do I turn that into 56000 dynes/(m/s)? That seems like a huge number for β, considering I used 0.4 in the last problem for β.
Thanks.
 
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  • #2
In principle, you do not have to convert any units, all the given values are consistently in CGS.

But if you want to, then the resistance is indeed 56000 dynes per m/s, but you need to finish the conversion to Newtons per m/s.
 

FAQ: ODE application of damped motion

1. What is damped motion in the context of ODE applications?

Damped motion is a type of motion where a system experiences a resistive force that causes it to gradually lose energy and come to rest. This is commonly observed in systems such as pendulums and springs, where friction or air resistance acts as the damping force.

2. How is damped motion described mathematically in ODE applications?

In ODE applications, damped motion is described using a second-order differential equation of the form mx'' + bx' + kx = 0, where m is the mass of the system, b is the damping coefficient, and k is the spring constant. This equation takes into account both the restoring force and the damping force acting on the system.

3. What are the different types of damped motion?

There are three main types of damped motion: underdamped, critically damped, and overdamped. Underdamped motion occurs when the damping force is less than the critical damping force, resulting in oscillations that gradually decrease over time. Critically damped motion occurs when the damping force is equal to the critical damping force, resulting in the system returning to its equilibrium position in the shortest amount of time. Overdamped motion occurs when the damping force is greater than the critical damping force, resulting in the system taking a longer time to return to its equilibrium position.

4. What factors affect the behavior of damped motion in ODE applications?

The behavior of damped motion in ODE applications is affected by several factors, including the damping coefficient, the mass of the system, and the initial conditions of the system. Higher damping coefficients and larger masses result in slower decay of motion, while certain initial conditions can lead to different types of damped motion.

5. How is damped motion used in real-world applications?

Damped motion is used in various real-world applications, such as shock absorbers in vehicles, vibration control systems in buildings and bridges, and seismometers for detecting earthquakes. It is also important in understanding the behavior of mechanical systems and designing efficient and stable systems.

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