Book Reference : Pages 45-46
To be able to answer the question “What is
What equipment do cars or bikes tend to have
to iron out the bumps in the road?
If the car suspension consisted only of
springs, what would happen to the motion
of the car for sometime after hitting a bump
in the road?
How would a pendulum continue to swing in
an “ideal physics world” with no friction & in a
What do we observe in the “real-world”
Most vehicles use springs or similar to iron out
the lumps and bumps
With only springs the vehicle will continue to
bounce (oscillate up and down) for some time
after hitting the bump and the passengers
would feel sea sick. Think SHM!
Pendulum would keep going with full amplitude
for ever
Friction and air resistance reduce the
amplitude until eventually the pendulum stops
Shock absorbers
Shock absorbers
In the “real-world” a system in SHM such as a
pendulum or a mass on a spring will eventually
come to rest due to “losing energy”, actually
doing work against friction and air resistance!
What will the ride in the car be like when
1. The damping is not strong enough
2. The damping is too strong
3. The damping is just right
No bears, kitchen furniture, porridge or small girls with golden
hair were harmed in the making of this lesson
[VPL Damping]
1. Light damping (under damping)
2. Heavy damping (over damping)
3. Critical damping
1. Light damping (under damping) The
oscillation slowly dies away (exponential
2. Heavy damping (over damping) The
damping is so strong that the displaced
object takes a long time to return to the
equilibrium position and does not oscillate
3. Critical damping : just enough to stop the
oscillation as quickly as possible often about
T/4 with little or no overshoot
What caused this?
How could it be avoided?
Caravan Stabiliser :
Friction is
introduced into the
tow mechanism to
damp both
sideways and up
and down motion
1) State is damping is light, critical or heavy in
these cases:
A child on a swing, displaced and released
Oil in a U shaped tube displaced from
equilibrium and released
2) What would happen if the oil in a damper
(shock absorber) was replaced with very
viscous (thick) oil?
1) A family car has an unloaded mass of 1000kg. The
mass is supported equally by 4 springs. When fully
loaded the total mass increases to 1250kg causing
the springs to compress by a further 2cm. When
the car hits a bump in the road it bounces. Find
the period of these oscillations.
State assumptions

Motion Along a Straight Line at Constant Acceleration