Work Physics | How easy to understand | What is work ?

Work Physics -Best definition. If you want to know, What is work ? and actual work meaning. So you are at right place for work definition physics. Because learn here, what is work done. And relation between work and energy.


Understand  work meaning in Physics


Work meaning- ” To do anything which involves mental or physical effort “.  But in Physics work is different, With normal definition of work. Because in Physics mental work is not considered work .Here i want to clear you, in day to day life, which you understand meaning of work is different in Physics.

Hence suppose if you are reading hard for your examination. So you are doing mental work, but in Physics meaning you are not doing any work. To understand Physics work, force and displacement are consider. See the above picture, how man is doing work ?whereas lady is not doing any work.


 Force and displacement meaning according to Physics 


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According to Physics definition of work = F⋅ S  or FScosθ, taking dot product of force and displacement. Where θ is angle between force and displacement vector. This is simple way to define work in Physics.

Some important points for work

 

Hence from the above figure. you have notice that, when force and displacement are parallel, then work is positive. And If force and displacement are anti-parallel, then work is negative. Another important point work is scalar quantity. Some people confused due to, sometime work is positive or sometime negative.

Because they thought that if work is positive, So its direction is toward right. And if it is negative then direction is towards left. But this is not correct at all. Because work is a scalar quantity, you can’t associate any direction with it. Work is calculate with the help of force and displacement.

Therefore force is a vector quantity, and displacement is also a vector quantity. But work is dot product of force and displacement, So it is a scalar quantity. Hence sign of work indicate, the direction of force and displacement. If work sign is positive then force and displacement direction are same.

And if it is negative, then force and displacement direction are opposite. This is true meaning of work sign.


 If force and displacement are perpendicular 


What is work ? You know work done formula is define as work  = Fscosθ, where θ is angle between force and displacement. So cos90° value is always zero. Hence work done in this case will be always zero. Therefore you can just refer the above first picture. why work done by lady is zero ?

Well this is simple, because force applied by lady in upward direction on the sack. Whereas she is moving  forward, so sack displacement is in the direction forward. Which is perpendicular to the applied force. Hence force and displacement are perpendicular in this case.

Therefore  work done by lady is zero. Hence lady is carrying sack from one place to other place, but she is not doing any work according to Physics definition.

But according to day to day life lady is doing hard work . I hope you have got the point.


 Force is applying but work done is zero how ?

See the above picture. A block is placed in the corner of the wall. And a man is pushing the block with 30N force. What will be work done by this man ? Well work done by man  Wman = Fscosθ. Now look here man is applying force but block does not displace.

Hence if displacement is zero, then work done by man will be obviously zero. Because work is directly proportional to displacement. So it is a important point . If displacement is zero, then work is zero. Even if force is applying or acting on the body. In normal language, this man is doing work.

But in Physics language, this man is not doing any work. Because displacement of block is zero.


If force and displacement are at some angle


A block of mass m is sliding on an incline plan as shown. What will be work done by mg force acting on the block. Hence work done will be W = Fscosθ. So put the value θ = 37° and m= 5kg , you will get W = mgscosθ = 5×10×5×cos37° = 250×cos37° = 250×4/5  = 50×4 = 200J.

Here i want to explain you this visualization in other way. Hence see the value F(scosθ), take (scosθ) together. So in this case (scosθ) is representing vertical height, that is 4m. Therefore put again the value of force mg and 4m, you will get the same work value.

So the formula of work done. You can write as W = F(scosθ)  = F(displacement along the force). Hence it is important point, If force vector and displacement vector are at some angle. Then work done can be written as W = F×(Displacement along the force).

Therefore in some situation it is difficult to find, displacement along the object movement. So in that case you can directly apply the concept of (Displacement along the force). And your problem will solve easily, Which is convenient to solve numerical problems. So remember this concept.


Important point regarding force and displacement 


When you define work done, dot product of force vector and displacement vector. Then s is displacement of point, where force acts. So you have to see, exactly the displacement of that point where force is acting.

From the above picture as shown. Man is pulling rope with a force of 100N. Hence block of mass 2kg is moving upward 2m as shown. Then you have to calculate work done by man. So can you tell, what will be work done by man ? Well  according to work done formula.

Work = Fscosθ, here F = 100N pulling downward and 2kg block is moving upward 2m. Hence angle between displacement and force is 180°. Therefore Work = 100× 2×cos(180°) = -200J.

So If you are calculating work done in this way, then it is WRONG. Now think why this is wrong ?

OK i already explained that you have to see, the force applied point and displacement exactly at that point. Hence force is acting on rope in downward direction. And rope is also moving in downward direction from force applied point. So work done by man W = Fscos0° = 100×2×1 = 200J.

If it is asked to you, what is work done by man on the block ? So it is clear that man is not doing work on the block. it is zero. Because man is not applying any force on the block directly. Man is only applying force on the rope. Then who is doing work on the block ?

This is rope tension force, which is doing work on the block.


Work and Energy 


The concept of work and energy is related to each other. Because force can do work on an object and cause a change in energy. And energy is ability to do work. Hence in simple, when you do work on an object, then its energy is changed. Therefore when energy is change then work is done.

Work done by friction force .  Do you know ? How do you walk on the ground ? Well due to friction force. You must know, without friction force you can’t walk on the ground.

But it is really interesting, friction force and displacement are in the same direction .Whereas work done by friction force is always zero. Because your one foot is always in contact with ground . And friction force act on that foot only.

Which is at rest . And your other foot is moving. Hence friction force work done is zero.

If you want more information about force and displacement. You can refer my previous post link below.

Force Concept 

Displacement concept

Friction Force concept


I will continue with other topic of Physics hidden concept . Always target to provide you my best effort.  So i hope  you have enjoyed learning about work Physics.  your feedback is important for me comment, likes and share. Thanks for sharing. Learn and grow.