Show that the following force is conservative

  • Thread starter nbram87
  • Start date
  • Tags
    Force
In summary, the homework statement is trying to determine if a force is conservative. It asks how to determine if the force is conservative, and shows that the curl of the force is zero regardless of the value of K.
  • #1
nbram87
8
0

Homework Statement



Fx = K(2x + y), Fy = K(x + 2y)

Homework Equations


The Attempt at a Solution


I think what is confusing me is that it is two different forces (Fx and Fy). I know that the curl has to be zero for it to be conservative, and I am assuming I will have to figure out a value for the constant K for that too happen.
 
Last edited:
Physics news on Phys.org
  • #2
Fx and Fy represent two components of a vector, so they describe a vector field. It might be written as:

## \vec{F} = Fx\;\hat{i} + Fy\;\hat{j} ##

How would you form the curl of that?
 
  • #3
I think that is one thing that is confusing me. How else could you determine that the force is conservative? Would you have to determine the work done by both Fx and Fy are equal to 0?
 
  • #4
nbram87 said:
I think that is one thing that is confusing me. How else could you determine that the force is conservative? Would you have to determine the work done by both Fx and Fy are equal to 0?

You could show that the work done in moving a particle along any closed path is zero (start at point P, traverse all possible paths (!) ending again at point P). The curl looks like the easiest approach.
 
  • #5
When you do the curl of Fx and Fy, I think the constant K becomes useless because it equals to zero. What is the meaning of K in the problem then?
 
  • #6
nbram87 said:
When you do the curl of Fx and Fy, I think the constant K becomes useless because it equals to zero. What is the meaning of K in the problem then?

I don't understand your meaning. How does K become zero? Can you show your curl calculation?
 
  • #7
Curl = d/dx(Fy) i - d/dy (Fx) j
= d/dx [K(x + 2y)] + d/dy [K(2x + y)]
= K(1+ 0) - K (0+1)
= 0
So K - K = 0?
 
  • #8
nbram87 said:
Curl = d/dx(Fy) i - d/dy (Fx) j
= d/dx [K(x + 2y)] + d/dy [K(2x + y)]
= K(1+ 0) - K (0+1)
= 0
So K - K = 0?

That tells you that the curl is zero no matter what value K has.
 
  • #9
Is it correct? Is my calculation of the curl and the value of K being meaningless correct?
 
  • #10
nbram87 said:
Is it correct? Is my calculation of the curl and the value of K being meaningless correct?

The curl calculation result is correct. K is not "meaningless" (it's a scaling constant for the magnitude of the force, and likely makes the force equation units balance). It simply turns out to be irrelevant to the question of conservation.
 
  • #11
Ok thank you.
 

What is meant by a conservative force?

A conservative force is one that does work only through a path-dependent change in potential energy. This means that the total work done by the force on an object is independent of the path taken by the object and only depends on the initial and final positions of the object.

What does it mean to show that a force is conservative?

To show that a force is conservative, we need to demonstrate that the work done by the force on an object is independent of the path taken by the object. This can be done by calculating the work done along different paths and showing that they all result in the same change in potential energy.

How do you prove that a force is conservative?

To prove that a force is conservative, we can use the fundamental theorem of calculus. This states that if a force can be expressed as the gradient of a scalar function, then that force is conservative. This means that if the force can be written as the negative gradient of a potential energy function, it is conservative.

What are some examples of conservative forces?

Some examples of conservative forces are gravity, electrostatic forces, and the force of a spring. These forces all have the property that the work done is independent of the path taken, as long as the initial and final positions of the object are the same.

Why is it important to determine if a force is conservative?

Determining if a force is conservative is important in many areas of science, including physics, engineering, and biology. It allows us to accurately predict the motion of objects and understand the behavior of physical systems. It also helps us to conserve energy and resources by identifying the most efficient paths and processes.

Similar threads

  • Introductory Physics Homework Help
Replies
7
Views
1K
  • Introductory Physics Homework Help
Replies
12
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
362
  • Introductory Physics Homework Help
Replies
21
Views
2K
  • Introductory Physics Homework Help
Replies
12
Views
1K
  • Introductory Physics Homework Help
Replies
1
Views
914
  • Introductory Physics Homework Help
Replies
6
Views
2K
  • Introductory Physics Homework Help
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
24
Views
1K
  • Introductory Physics Homework Help
Replies
4
Views
1K
Back
Top