The frictional force acting on the drum set does negative work. Does friction always do negative

The frictional force acting on the drum set does negative...

Key Concepts

Work

Work is the mechanism through which energy is transferred by a force acting over a displacement, mathematically represented by the dot product of the force and displacement vectors. The sign of the work depends on the direction of the force relative to the displacement, being positive when the force component is in the direction of the displacement and negative when it is opposite.

Friction

Friction is a force that arises from the interaction between surfaces in contact, often opposing their relative motion. There exist different types of friction, such as static friction (which prevents motion until a threshold is reached) and kinetic friction (which acts during sliding motion), each affecting the energy of a system in different ways.

Positive and Negative Work by Friction

While friction commonly does negative work by opposing motion, it can do positive work under certain conditions. For example, static friction can do positive work when it acts in the same direction as an object's displacement, such as in the case of a car accelerating forward where the frictional force between the tires and the road contributes to the car’s motion.

Transcript

00:01 In this video, we are going to focus on finding out about the work done by friction.

00:05 And here we can firstly take a hypothetical example.

00:09 Suppose we are having a block which is having some mass m.

00:12 Then if we draw its free body diagram, then there will be one force acting in the downward direction, which will be mg.

00:19 And there will be one force, suppose, and it is here f.

00:23 So with this very force, we are pulling this very block to the right hand side.

00:28 Then if the ground is having friction, then friction will act in the left -hand side because it opposes the relative motion.

00:37 Now here we can say that there will be normal reaction on this very block and it will be denoted as such.

00:45 So now we are talking about the work done by friction, right? we know the formula that work done is here equals to, let us write, it will be here force multiplied with displacement.

00:58 So it can be here written like this, right? we have to take their dot product.

01:05 So whenever we take dot product, then we consider the angle.

01:08 Basically, we consider cosine of theta.

01:11 So here, in this very case, if we consider the theta value, so theta is basically the value between force as well as we can say displacement.

01:22 So if the block is here moving in the forward direction, that is in the right hand direction, then the angle between the force and the displacement, basically if we consider about the force of friction, because we are here talking about the work done by friction, right? so here we will consider the value of force to be equals to small f.

01:44 So let us assume that this is f1 to avoid confusion because here we have written f as the force...

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