Chapter 8.1 and 8.2 Torque and Angular Rotation
Chapter 8.1 and 8.2 Torque and Angular Rotation. Definition of Torque Torque is the quantity that measures the ability of a force to rotate an object.
Dec 18, 2015
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Chapter 8.1 and 8.2Torque and Angular Rotation
Definition of TorqueTorque is the quantity that measures the
ability of a force to rotate an object around some axis (fulcrum). ◦ Units – Nm
Lever arm is the perpendicular distance from the axis of rotation to a line drawn along the direction of the force.
Torque depends on Force and the length of the lever arm.
Torque = Force x lever arm τ = Fr
Torque (cont.)◦Only the perpendicular component of
the force produces a torque.◦The lever arm is the distance
between the point where the force is applied and the axis of rotation (known as the fulcrum).
◦By convention, we treat counterclockwise torque as positive, clockwise as negative.
◦Torque like displacement and force is a vector quantity
Sample problem 1Find the torque produced by a 3 N
force applied to a door at a perpendicular distance of 0.25 m from the hinge.◦Known?
F = 3N, d = 0.25m
◦Unknown? τ = ?
◦Equation? τ = Fd τ = 3 (.25) = 0.75 Nm
Torque problem 2 In the picture below, the person on the left weighs
900 N, and the person on the right weighs 400 N. If the person on the right is sitting 3 m from the fulcrum and the seesaw is balanced, how far must the person on the left be from the fulcrum? ◦ Known: Equation: Fr = Fr
◦ Unknown:
Chapter 8.3Center of Mass
The Center of Mass
SECTION
8.3 Equilibrium
The center of mass of a person varies with posture.
For a person standing with his or her arms hanging straight down, the center of mass is a few centimeters below the navel, midway between the front and back of the person’s body.
The Center of Mass of a Human Body
SECTION
8.3 Equilibrium
When the arms are raised, as in ballet, the center of mass rises by 6 to10 cm.
SECTION
8.3 Equilibrium
The Center of Mass of a Human Body
By raising her arms and legs while in the air, as shown below, a ballet dancer moves her center of mass closer to her head.
SECTION
8.3 Equilibrium
The Center of Mass of a Human Body
The path of the center of mass is a parabola, so the dancer’s head stays at almost the same height for a surprisingly long time.
SECTION
8.3 Equilibrium
The Center of Mass of a Human Body
Center of Mass and Stability
Click image to view movie.
SECTION
8.3 Equilibrium
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