Negative Velocity, but not Speed

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Negative Velocity, but not Speed

Name: Terry B.
Status: student
Age: N/A
Location: N/A
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Question:

in the question already on the site : Is there a negative velocity? if so how is it achieved?

http://www.newton.dep.anl.gov/askasci/phy99/phy99413.htm

John Hawley states, logically, you cannot have negative speed.

However, with the current Hurricane over the US Eastern seaboard site:

http://www.wunderground.com /radar/radblast.asp?zoommode=pan& prevzoom=zoom&num=1&frame=0&delay=15&scale= 1.000&noclutter=1&ID=DIX&type=N0V&showstorms=99&lat=40.72409821&lon=-74.17324829&label= Newark,%20NJ&map.x=400&map.y=240&scale=1.000¢erx=400¢ery=240&showlabels= 1&rainsnow=0&lightning=0&lerror=20&num_stns_min=2&num_stns_max=9999&avg_off=9999&smooth=0

quotes wind velocity of -64 knots to +64 knots (if I read it correctly).

Replies:

Speed is path length (distance) divided by time. Neither quantity can be negative. Hence, speed is always positive.

Velocity is the displacement (change in position relative to a reference point) divided by time. You can have a negative change in position, giving a negative velocity.

Nathan A. Unterman

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Update: June 2012