Torque Web Quest
Helpful Hints
Part I: Definition of Torque
Torque is defined as the tendency to
produce a change in rotational motion.
Examples:
Torque is Determined by Three Factors:
• The magnitude of the applied force.
• The direction of the applied force.
• The location of the applied force.
Each
The
of theforce
20-N the
The 40-N
forces
nearer
produces
forces
a different
the
end of has
thetwice
wrench
torque
as does
due
totorques.
the
the
have greater
20-N force.
direction
of force.
Magnitude
Location
ofForce
of
force
force
Direction
of
20 N q
2020
N
20NN
20
40NN
20 N
20 N
q
Units for Torque
Torque is proportional to the magnitude of F and to the distance r from
the axis. Thus, a tentative formula might be:
t = Fr
Units: Nm or lbft
t = (40 N)(0.60 m)
= 24.0 Nm, cw
6 cm
t = 24.0 Nm, cw
40 N
Sign Convention for Torque
By convention, counterclockwise torques are positive and clockwise torques
are negative.
ccw
Positive torque: Counterclockwise, out of page
cw
Negative torque: clockwise, into page
Part II: Moments of Inertia
• The moments of inertia for many shapes
can found by using the following:
– Ring or hollow cylinder: I = MR2
– Solid cylinder: I = (1/2) MR2 (use for part II in
lab)
– Hollow sphere: I = (2/3) MR2
– Solid sphere: I = (2/5) MR2
Rotational Inertia
• A rotating mass on a rod
can be described with
variables from linear or
rotational motion.
Rotational Inertia
• To put the equation into rotational motion variables, the
force is replaced by the torque about the center of
rotation.
• The linear acceleration is replaced by the angular
acceleration.
Linear and Angular Acceleration
Angular acceleration
(kg)
Linear
acceleration
(m/sec2)
a=ar
Radius of motion
(m)
Rotation and Newton's 2nd Law
• If you apply a torque to a wheel, it will spin in the
direction of the torque.
• The greater the torque, the greater the angular
acceleration.
Part III: Angular
Momentum
• Momentum
resulting from an
object moving in
linear motion is
called linear
momentum.
• Momentum
resulting from
the rotation (or
spin) of an object
is called angular
momentum.
Calculating angular momentum
Angular momentum is calculated in a similar way to
linear momentum, except the mass and velocity are
replaced by the moment of inertia and angular
velocity.
Angular
momentum
(kg m/sec2)
L=Iw
Moment of
inertia
(kg m2)
Angular
velocity
(rad/sec)