Damped oscillations - science

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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
 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.
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.
Penny Farthing
Rubber wheels made this more
comfortable – for a while
The Pneumatic-Tyre
From the 1890’s air was used is the tyres
– for added comfort
Suspension Bikes
Suspension is used now on bikes –
especially those that are designed to go
off road
Suspension
Spring suspension is made up of two parts
A spring
And a shock absorber – or Damper
Why?
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
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
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
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)
Amplitude of damped oscillations
Light
Critical
Heavy
Light
Critical

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