Sometimes
we
need
to
transmit
rotation
from
one
____________________
of
rotation
to
another
.
For
example
,
there
may
be
a
distance
or
an
angle
between
two
____________________
and
they
may
not
be
totally
aligned
.
In
these
cases
,
we
can
use
various
coupling
mechanisms
.
Rigid
couplings
form
a
permanent
connection
between
two
shafts
.
These
shafts
may
have
different
diameters
,
but
they
must
be
perfectly
aligned
.
Clutches
form
a
rigid
connection
which
isn't
____________________
.
For
example
,
a
car
has
a
clutch
that
engages
and
disengages
the
engine
and
the
wheels
.
This
system
also
permits
various
combinations
that
change
the
gear
ratio
between
the
engine
and
the
wheels
.
This
is
similar
to
the
gear
system
of
a
bicycle
.
Friction
clutch
The
ends
of
two
____________________
come
into
____________________
.
When
one
____________________
turns
,
there
is
friction
.
This
turns
the
second
____________________
.
Jaw
clutch
.
The
ends
of
two
shafts
are
connected
by
____________________
____________________
.
A
jaw
clutch
is
more
reliable
because
it
doesn't
slip
easily
.
Flexible
couplings
are
also
useful
.
Oldham
coupling
An
____________________
coupling
is
used
to
connect
____________________
that
are
not
perfectly
____________________
.
The
grooves
permit
____________________
movement
.
Cardan
joint
A
____________________
joint
connects
two
____________________
that
are
at
an
____________________
to
each
other
.
____________________
joints
are
used
in
cars
.
They
transmit
rotary
motion
from
the
car's
engine
to
its
back
wheels
.
