What are Some Examples of Conservation of Energy in Real Life Scenarios?

[feedmeister]

Hi all,

I'm just working some practice problems, and I can't think of any examples for these two questions. Any help?

Homework Statement

Give a specific example of a situation in which:

W_{ext}\rightarrow E_{th} with \Delta K=0, and \Delta U=0.

U\rightarrow E_{th} with \Delta K=0, and W_{ext}=0.

Homework Equations

K-f + U_f + Delta E_th = K_i + U_i + W_ext

The Attempt at a Solution

I'm trying to find examples of these situations... any help?

Thanks!

 

[dynamicsolo]

Give a specific example of a situation in which:

W_{ext}\rightarrow E_{th} with \Delta K=0, and \Delta U=0.

Can you think of something where you would be pushing it without having its kinetic energy or potential energy change at all, so that all your work just goes into, say, heating the surfaces in contact?

U\rightarrow E_{th} with \Delta K=0, and W_{ext}=0.

How about something where the potential energy being released only goes into heating up contact surfaces, without having the kinetic energy change and without something actively pushing it along?

 

[feedmeister]

Hey,

Thanks for the response. I know what the question is asking, but I can't think of situations in which they occur.

Thanks

 

[dynamicsolo]

Hey,

Thanks for the response. I know what the question is asking, but I can't think of situations in which they occur.

Well, for the first one, how about pushing a table across a carpet or a rough floor so that it moves at only a constant velocity?

The second one would involve something falling through a rough passage or through a viscous fluid at terminal velocity, so that the change in potential energy is dissipated as heating or disturbance in the fluid, without the object gaining speed.

 

[feedmeister]

Wow, thanks dynamicsolo, I've been trying to think of scenarios in which those cases would happen, but I never thought to have constant velocity and have it fall through something.

I appreciate your help!