α is the angular acceleration, defined as the rate of change of angular velocity, ω.
If the increase in ω is clockwise then the vector for α points away, that is, α is negative.
On the other hand, if ω is counterclockwise, then α points towards the observer, hence, positive.
Figure 1 shows four rotating wheels. For each, determine the signs (+ or -)of ω and α.
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What scientific concept do you need to know in order to solve this problem?
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