Transcript Forces in Tow - Drexel University

Torqued
An investigation of rotational motion
Think Linearly
• Linear motion: we interpret
– position as a point on a number line
– velocity as the rate at which position increases
– acceleration as the rate at which velocity increases
http://education.yahoo.com/homework_help/math_help/problem?id=minialg1gt_11_1_1_15_100
Angular Quantities
• Rotational motion: based on the radius of the
rotating object and the number of revolutions it
passes through, we can relate
– position
angle
r
– angular velocity
velocity
– Angular acceleration
acceleration
• For a disk of radius r:
#angles in one revolution
# revolutions
Name this formula!
2 rad 2  r m
1 rev 

 2r m
1 rev
2 rad
Linear distance
Torque
• Torque, T, occurs when forces do not occur at an
object’s center of mass (balance point).
– T=F*d, where F is a force and d is distance from center
of mass
• Torque-angular acceleration: T=I*α
• Compare to Newton’s 2nd law: F=m*a
• Torque is defined by the direction the load may
rotate an object:
– CCW is (+)
– CW is (-)
F
F
r
r
F
F
r
r
F
F
r
2r
How do you think these disks will rotate?
Activity Purpose
• We will use weights to rotate the drive axle of
our mousetrap cars.
• We can record the acceleration of the falling
weight and compare this to the torque
provided by the weight in order to calculate
the Moment of Inertia of the axle.
Hypothesis
**Think about these questions**
Which type of axle will have a larger moment
of inertia -- one with large wheels or one with
small wheels?
Do you think the mass of the axle assembly
(axle + wheels) affects the moment of inertia
more or less than its size?