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Xylem101
Registered User Posts: **868** Member

I saw a question that asked to give an example of friction doing +ve Work, how is this possible and Give me an example if it is...

Post edited by Xylem101 on

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## Replies to: Can Friction do Positive WorK?

743Member172Junior Member868Member9,259Super Moderator1,313Senior Memberxylem: force of friction is in the opposite direction of the motion... so if you move a block to the right (+) friction does - work... if you move the block to the left (-) the friction does + work

80Junior Memberwhen you sum the forces, friction is a negative force because postitive forces are in direction of motion. theta is the angle between friction and r, your displacement. Since friction is in the direction opposite displacement, theta= 180 and work is thus negative. Therefore, friction always does negative work.

1,313Senior Member80Junior MemberAnother way of looking at it is with the equation Work=magnitude of friction*magnitude of r*cos180. In this equation, you only look at the MAGNITUDES of friction and r, which are always positive. In this case, cos 180 gives you the negative sign and Work done by friction is still negative.

The cos 180 tells you that friction is always opposite the direction of displacement.

1,313Senior Member268Junior Member1,975Senior Member124Junior Member1,084Senior Member