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Damped oscillations

Damped oscillations. Objective (k) describe the effects of damping on an oscillatory system. Outcomes. ALL MUST Be able to define damping. Be able to understand where damping may occur. Be able to understand what an exponential relationship is. MOST SHOULD

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Damped oscillations

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  1. Damped oscillations Objective (k) describe the effects of damping on an oscillatory system

  2. Outcomes • ALL MUST • Be able to define damping. • Be able to understand where damping may occur. • Be able to understand what an exponential relationship is. • MOST SHOULD • Be able to describe an investigation where damping is caused (i) by the drag of the air and (ii) by eddy currents (electromagnetic damping). • To show that for light damping, the amplitude of oscillations decays exponentially with time.

  3. The Velocipede • Or Boneshaker from the 1860’s • Its adjustable wooden seat has no springs under it: hence it was known as a "boneshaker". Lacking the comforts of the modern bicycle, it has been relegated to the museum.

  4. Penny Farthing • Rubber wheels made this more comfortable – for a while

  5. The Pneumatic-Tyre • From the 1890’s air was used is the tyres – for added comfort

  6. Suspension Bikes • Suspension is used now on bikes – especially those that are designed to go off road

  7. Suspension • Spring suspension is made up of two parts • A spring • And a shock absorber – or Damper • Why?

  8. Suspension • Springs are good at absorbing energy • But not so good at dissipating it • You want to absorb an impact • But then don’t want the spring to keep bouncing • The oscillations must be damped

  9. Dampers (Shock absorbers) • Using oil (a viscous fluid) Which is a sticky substance that objects can’t move through easily Here, the spring takes the shock and then its oscillations are slowed with oil

  10. Other examples • Compressed air shocks • Spring shocks – a pair of springs working against each other • Electromagnetic damping – using a magnetic field to slow oscillations (used in Galvonometers) • The paper cone of a loud speaker vibrates but is heavily damped as it transforms its kinetic energy into sound energy in the surrounding air

  11. Oscillations and damping • In S.H.M, (i) the period is independent of the amplitude and (ii) the total energy remains constant • In practise many objects only undergo approximate s.h.m because (i) the restoring force is not exactly proportional to the displacement and (ii) resisting forces oppose the motion (e.g. air resistance)

  12. Amplitude of damped oscillations • Light • Critical • Heavy

  13. Light

  14. Critical

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