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 – angular velocity velocity– Angular acceleration acceleration

• For a disk of radius r:

r

m2rad

m

2

2

rev

rad

1

2rev1 r

r

# revolutions

#angles in one revolution Name this formula!

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 (-)

r r

F F

r r

F F

r 2rF F

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?