work done by friction is always negative,why?

Answer 1

The technical answer is that friction opposes motion and hence does negative work.

But what does negative work really mean? After all, it's not a vector, so the negative sign doesn't tell us that it's going backwards.....

The easiest and best way to look at friction is as a nonconservative force. I won't give you the fancy definition here... just remember the two types of NC forces most used in physics textbooks...

Friction (work is negative)
Applied force, such as pushing or pulling by a human (work is positive)


In the case of friction, energy is being REMOVED from the system. That's why it's negative, to show that, as time goes on, friction is steadily taking away energy from the system.

However, let's say you're pushing a swing. Then you're applying a force. Each time you push the swing, you add energy to the system. If you didn't continually push the swing, friction would remove all the energy and the swing stops. So you continually add energy to the swing to keep it in motion.


Simple answer: Friction does negative work because it is removing energy from the system.

Answer 2

Friction ALWAYS opposes motion. If you call the direction the object is traveling positive, Friction Force is always negative. In conservation of energy problems, Ei = Ef + l Wnc l. l Wnc l is absolute value because the formula for work, W = Fdcos#, the cos takes into account the direction of the displacement and the forces.

Answer 3

If a body moves in one direction, friction is the force that acts against it. Friction acts against the force of a body and thus harms it just like if we are applying a force on a person during a fight, he will apply an opposite force on us to push us back. This is how friction works and harms.

Answer 4

Because friction always opposes motion and hence does negative work. The energy gets converted into heat, and is a good example of the 2nd law of thermodynamics.

Answer 5

Work is always positive from one point of view and negative from another. Friction in your car's brakes takes kinetic energy away from the car and adds heat energy to the brakes and the air. From the air's point of view it is positive work.

However, the net result of friction is entropy. The energy ends in a less useful form. So, althought energy is concerved, it's usefulness is not. The same is true of all work, except that we put the waste products out of our mind until they come back to haunt us as pollution.

Answer 6

because friction means d force which opposes. so if friction acts then it acts opp 2 the force and creates negative work

Answer 7

work done by friction is always negative because it opposes d motion of d body. so d wrk is done against d motion of d body. which means that d work done is negative. if d wrk wud hv been positive then d body wud never stop due to friction n on d contrary wud gain speed.

Answer 8

Conservation of Energy. If friction force was in the direction of movement, then the object would continue to accelerate forever.

Answer 9

its so because the friction always works opposite to the direction of force applied.

Answer 10

work done by friction is always negative because it opposes d motion of d body. so d wrk is done against d motion of d body. which means that d work done is negative. if d wrk wud hv been positive then d body wud never stop due to friction n on d contrary wud gain speed.