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Circular motion and SHM
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Created by
Theo Kitching
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For something moving in a
circle
, there must be a force
continuously
acting at
90
degrees to the object's
velocity
or
direction
of motion
Velocity and direction of travel constantly
change
, but the object still travels at a
constant
speed
Velocity is a vector, so it's still
accelerating
because the
direction
of the
velocity
is
changing
, even though the speed is
constant
Centripetal
acceleration
is equal to
V^2
/
R
, where
R
is the
radius
of the
circle
Centripetal force
is
equal
to
mv^2
/
R
Angular velocity
(angular speed or angular frequency) is represented by the symbol
Omega
(Ω), which is equal to
2π
/
T
(radians per second)
V =
Omega
*
R
Simple harmonic motion
(
SHM
) describes any object oscillating around a point like a
pendulum
or a
mass
on a
spring
Acceleration in SHM is
proportional
to the object's
displacement
from
equilibrium
and in the
opposite direction
to the displacement
Restoring
force in
SHM tries to return the object
to
equilibrium
Equation for SHM:
a = -Omega^2 * x
Maximum acceleration
occurs at the
maximum displacement
(amplitude)
Equation for time period of a pendulum: T =
2π
* sqrt(L / g), where L is the
length
of the string and g is
gravitational field strength
Equation for time period of a mass on a spring: T =
2π * sqrt
(
m / k)
, where
k
is the
spring constant
For a
pendulum
, the frequency is
inversely
proportional to the
length
Damping
force
opposes
the
motion
of the object and removes
energy
from the system
Light damping
gradually
decreases
the
amplitude
of
oscillations
Heavy damping quickly reduces
the
displacement
of the object
Critical damping
stops the object at
equilibrium
as quickly as possible
Resonance
occurs when an
external force
drives the
oscillations
,
increasing
the
amplitude
and adding
energy
into the system
Maximum resonance
occurs when the
driving force frequency
matches the
natural frequency
of the system
Driving force and restoring force are
90
degrees
out of phase
with each other during
resonance
Resonance
is most effective when the system is
lightly damped
Resonance graph
shows the
highest amplitude
when the
driving frequency
equals the
natural frequency
Adding more damping
decreases
the
height
of the
resonance peak
Peak width
does not change with
increased damping
Energy
is
proportional
to the
square
of the
amplitude
in a
damped
system
Total energy
remains
constant
in a
closed system
with no
energy loss
to the
surroundings