16.7 Damped Harmonic Motion

16.7 Damped Harmonic Motion

  • The period of the motion is the same as the period of the oscillator.
    • The period is determined using the relationship between uniform circular motion and simple harmonic motion.
  • The connection between uniform circular motion and simple harmonic motion is sometimes referred to in some modules.
    • You will find this relationship useful if you carry your study of physics to greater depths.
    • It can help to understand how waves add when superimposed.
  • You could attach a pen to the outside edge of the turntable by attaching a rod to it.
    • The pen will move as the player turns.
    • The paper can be dragged under the pen to capture its motion as a wave.
  • The mom needs to keep pushing the swing.
  • A guitar string stops after being plucked.
    • You have to keep pushing to make a child happy on the swing.
  • We can often make non-conservative forces negligibly small, but completely undamped motion is rare.
  • We might even want to damp oscillations, such as with car shock absorbers.
  • The non-conservative force removes energy from the system.
  • The negative is due to the removal of mechanical energy from the system.
  • The period and frequency will be affected if you increase the amount of damping in the system.
    • The system doesn't move toward equilibrium if there is large damping.
    • The system will return to equilibrium faster but will overshoot and cross multiple times.
    • It may overshoot the equilibrium position, but will reach equilibrium over a longer period of time.
  • There is a difference between time and displacement for a critically damped harmonic oscillator.
    • The critically damped oscillator can return to equilibrium in the smallest time possible.
  • A system that returns to equilibrium rapidly and remains at equilibrium as well is often desired.
    • 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 moving about the new position.
    • When standing on a bathroom scale with a needle gauge, the needle moves to its equilibrium position without moving.
    • If the needle moved for a long time before it settled, it would be inconvenient.
    • In character, damping forces can vary greatly.
    • Most places in this text assume that Friction is independent of velocity.
    • Many of the damping forces depend on velocity.
  • The ability to control the motion is important in many systems.
    • This can be achieved using non-conservative forces such as the friction between surfaces.
  • An object attached to a spring is shown to have a transformation of energy.
  • You have to integrate your knowledge of various concepts.
    • The first thing you need to do is identify the physical principles involved.
    • The first part is about the force.
    • This is a topic about the application of laws.
    • Part (b) requires an understanding of work and the use of energy.
  • We need to identify the knowns and unknowns for each part of the question, as well as the quantity that is constant in Part (a) and Part (b) of the question, now that we have identified the principles we must apply in order to solve the problems.
  • The proper equation is Friction is.
  • The values should be identified.
  • The coefficients are small and the force is small.
  • The system involves elastic potential energy, as the spring expands, as the body speeds up, and as the body slows down.
  • Friction is a non-conservative force and energy is not conserved.
  • The motion is horizontal, so it doesn't need to be considered.
  • The energy in the system starts from rest.
    • The total distance traveled and the force of friction are how this energy is removed.
  • The distance can be solved by equating the work done to the energy removed.
  • The initial, stored elastic potential energy is equal to the work done by the non-conservative forces.
  • The total distance traveled back and forth across is the undamped equilibrium position.
    • The number of oscillations about the equilibrium position will be more than if the amplitude is decreasing.
    • The system won't return for this type of force at the end of the motion because it will exceed the restoring force.
    • The system is not sound.
    • An overdamped system with a simple constant damping force wouldn't cross the equilibrium position.
    • If the system had a 20 times greater damping force, it would only move 0.0484 m toward the equilibrium position.
  • This example shows how problem-solving strategies can be used to integrate different concepts.
    • Identifying the physical principles involved in the problem is the first step.
    • Problem-solving strategies are used in the second step to solve unknowns.
    • Many worked examples show how to use them in a single topic.
    • You can see how to apply the integrated concepts in this example.
    • These techniques are useful in applications of physics outside of a physics course, in other science disciplines, and in everyday life.
  • When an object is moving, friction can come into play.
    • Friction causes a problem.