I Measuring energy and its change

  • Thread starter fog37
  • Start date
800
36
Hello Forum,

I understand that energy, either kinetic is a relative quantity whose value depends on the frame of reference and its motion. Is that true for potential energy as well?

I read on a physics book that only changes in energy can be measure. What does that exactly mean? Why can we not measure energy directly but only its changes? Energy is apparently the measure of change of a system. What matters are energy differences and energy changes. Is it not correct to state that a system has a certain amount of energy at a particular time? Should we only talk about energy gains and energy losses for a system?

Thanks!
 

anorlunda

Mentor
Insights Author
Gold Member
6,291
3,497
Mechanical potential energy is also relative. Consider the gravitational potential energy of a book on a shelf. We arbitrarily assign one of the shelves as zero.

There are many forms of energy other than mechanical PE and KE. Electrical, chemical, heat, nuclear ...
 
800
36
Thanks anorlunda.

I would say that all forms of energy can be derived from kinetic and potential. For example, temperature is microscopically tied to kinetic energy. Bonds in molecules to potential energy...

I am still not sure why we can only measure energy changes only and not the particular energy of a system...
 
800
36
Thank you. Very interesting.

It still does not seem to address, unless I have missed it, why energy changes is all we can measure and worry about and why energy is a measure of the change in a system while force the agent of change...
 

PeroK

Science Advisor
Homework Helper
Insights Author
Gold Member
2018 Award
9,067
3,274
Thank you. Very interesting.

It still does not seem to address, unless I have missed it, why energy changes is all we can measure and worry about and why energy is a measure of the change in a system while force the agent of change...
So, what would you say is the absolute energy of, say, the Solar System? Something that is not frame dependent.

You said:

I would say that all forms of energy can be derived from kinetic and potential.
So, what are you going to do to establish an absolute kinetic energy of the Solar System?
 

Want to reply to this thread?

"Measuring energy and its change" You must log in or register to reply here.

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top