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“N t disturb. I m very busy with work. What i need to make a video video and work today alright. Let s get started.

Then hi friends in this video. ll be doing. The physics definition of work the formulas to calculate work done. And then we ll do our top three test oriented questions on this topic.

I m sure by the end of this video. The concept of work will be really clear to you now what comes to your mind. When you hear the word work are you thinking about your homework or the work of cleaning up your room for me. My work.

Today is to make this video for you. The physics definition of work is very different from our everyday. Use of the term work in physics work is done. When there is a force.

And there is a displacement and want the formula to calculate work done is force into displacement in the direction of the force to understand this. Let s do a simple experiment together for that i need you to get an object like a book. So pause. The video right here and go and get a book.

So are you ready with your book. I m ready with mine otherwise. Pause. The video here and go.

And get a book. Now. When you hold the book. Like this are you doing any work right now.

The answer s no because there s no displacement of the book..

But if you go ahead and lift up the book like this have you done any work now. The answer is yes. Because there is a force involved and there is a displacement. So you can feel the force when you re lifting the book.

And this is your display smelled of the book so let s say my kiss. The force is about ten newton and the displacement from here to here is forty centimeters. So how much work have i done. Let s use the formula work equal to force into displacement.

So that s ten newton into forty centimeters now i need to convert that to. Si unit so it s 04. Meter so i get ten newton into 04 meter. Which is four newton meter.

And we know that newton meter. Is basically. June. Which is the si unit of work.

So i ve done. Four joules of work right. Here. Let s put this important formula of work done on our concept board.

Let s also place the si unit of work done. Which is joules. I stole my daughter s toy for this demo. So if i pull the toy like this i m doing work as you can see force and displacement are in the same direction.

Here. Now an interesting question is is it possible that force and displacement are not in the same direction. What do you think the answers yes let me show you so suppose if i now pull the toy like this as you can see my force is along the string. But the displacement is along the table so there s an angle between the force and the displacement.

Here now how do we calculate the work done for this case..

So. Let s zoom in and see so as we saw here. Force is along the string and the displacement of the toy is along the table here to make it easy rather than finding the displacement in the direction of the force. We are going to find the force the direction of the displacement.

So for that i want you to consider this right angle triangle here. Where here s the right angle. And here s the angle theta between the force and the displacement. So as you can see the forces along the hypotenuse of the triangle.

But we have interested in finding the force along the displacement or along the base of this right angle. Triangle. So. What will be the component of the force along the base that s right.

It s going to be f into cos theta. So what will be the work done here. It s going to be f cos theta into the displacement. So if i rearrange that i m going to get w.

Equal to f s. Cos theta. Where theta is the angle between the force and the displacement. Let s put this formula onto our concept board.

This first formula works only when force and displacement are in the same direction the second formula w equal to fs cos theta is more powerful and works for any angle between the force and the displacement. Let s look at three cases. Where we can apply this second formula case. One so when i push this block along the table like this as you can see that the force and displacement are along the same direction.

So what is the angle between the force and the displacement here that s right it s zero degrees. So if we use our general formula. Our work. Done will be w.

Equal to f..

S. Cos. Theta. And we know that the angle.

Theta is zero here and cost zero is 1. So we get w. Equal to f into s. Which is basically the first formula that we did in this video case to suppose a person is walking carrying a bag as shown in the picture here so to find the work done we need to look at the force and the displacement here.

So what is the direction of the force so since he is holding the bag. The force is in the vertically upward direction. And the displacement is along the path. He s traveling now what is the angle between the force and the displacement here that s right the angle is 90 degrees.

So now let s use our formula w equal to fs cos theta and we know that cos 90 is zero so the work done actually turns out to be zero in this case. Now. How is that possible is there any other force for which he s doing nonzero work. The answers yes.

It s the force of friction. So when he s walking along the path. He s doing nonzero work against the force of friction. So an important exam.

Tip is that to find the work done you need to carefully consider the force involved and the displacement case three if i lift the book. Like this. What is the work done by the force of gravity here. So last time.

We looked at what is the work done by us. But now we re interested in the work done by the force of gravity. So what is the direction of the force of gravity. That s right it s vertically downwards since it s the weight of the book.

But what was the direction of the displacement here as you saw it s vertically upwards..

So the force of gravity and the displacement here are in opposite directions. So what is the angle between force and the displacement. It s not zero degrees. It s going to be 180 degrees here so now let s use our formula w equal to fs cos theta and we know that cos of 180 is minus one so the work done in this case turns out to be negative since force and displacement are in opposite directions.

So we ve learnt that work done can be both positive and negative. So let s put all these three cases onto our concept board. So this is the concept board that we built along in this video. I would encourage you to pause here and take down notes.

Now that we have finished the concept of work and the formulas to calculate work. Done. Let s move on to our top three exam oriented questions on this topic. Here are the top three questions.

I encourage you to pause. Here and try to solve these questions. I ll be posting a video on the solution. Soon you can find a link to the solutions video in the description below or search for it on my channel page.

So i hope. The concept of work is super clear to you now. And do remember that the physics work is very different from our everyday use of the term work in this video. We ve learned that work done is force into displacement.

There s a second formula to calculate the work done. Which is change in energy or to be more specific change in kinetic energy. So if you want to learn more about that you can watch my video on energy. I ll be putting a link in the description below.

And i have a little work for you at the end of this video. Which is to like comment and share this video and also subscribe to my channel thanks for watching. ” ..

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