Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

I think that both force (number of newtons) and power (p=ui(?)) implies that there is energy so we can't have force without energy and we can't have power without energy(?)

But can there be energy that is energy and no force and no power?

share|improve this question
4  
I'm having trouble understanding your question. Force is defined as the rate of change of momentum and power is the rate of change of energy. If force/power are zero that implies that the momentum/energy resp. are constant, not absent... And energy is energy tautologically. What do you have in mind for energy that is not energy? –  Michael Brown Mar 16 '13 at 13:44
    
Exactly what I had in mind was whether I'm correct in presuming the existence of energy based on the knowledge that there is some force or some power. I'm trying to know what I can know if neither force nor power are mentioned while energy is the topic. –  909 Niklas Mar 16 '13 at 13:56
3  
If I throw a ball in outer space, it has energy (1/2 mv^2), and if it never interacts with anything else, it will have no force and no power. @Nick, I think if you provide some physical examples to illustrate what you are asking, it may help us understand. –  Mew Mar 16 '13 at 15:07
    
I wonder how e.g. radiation can be a power or a newtonian force. We can get radiation from the creation of the universe but we can't really call that radiation a newtonian force or a power from the big bang or can I say that the big bang is causing newtonian movements today(?) e.g. is radiation a newtonian movement(?) –  909 Niklas Mar 16 '13 at 15:48
2  
A single photon of radiation has a constant energy E = hf, and there will be no force or power if this photon does not interact with anything. However most radiating sources, are releasing many photons per second, and therefore one attributes "Power" to the source, which is related to the number of photons emitted per second. In the case of the Sun, the sun is losing its internal energy, and transferring the energy to light over time, and therefore has "Power". Each individual photon of light however does not have force or power until it interacts with something else. –  Mew Mar 17 '13 at 0:17
show 1 more comment

2 Answers

up vote 1 down vote accepted

You ask:

I wonder how e.g. radiation can be a power or a newtonian force. We can get radiation from the creation of the universe but we can't really call that radiation a newtonian force or a power from the big bang or can I say that the big bang is causing newtonian movements today(?) e.g. is radiation a newtonian movement(?)

Radiation classically carries energy and if the radiation interacts with a body, then power is transmitted , where power is the rate of change of energy. For example there is radiation pressure in vacuum , in this link. Radiation does transfer energy in a newtonian way, where the force can be estimated from dp/dt, the instantaneous change of momentum .

The big bang is not a simple story to be expounded here and used as an example. Have you read the wiki article?

But can there be energy that is energy and no force and no power

Yes, as said in the comments to your question only interactions need the concept of force and power.

share|improve this answer
add comment

A body when is in equilibrium and is still in a state of motion may have energy but has 0 net force. And Power is work done per unit time and in many cases work is done changing type of energy. If a body is in equilibrium, a body is most possibly in uniform motion, so energy is not getting transformed into anything else, thus there is no change in amount of energy resulting no work done i.e. no power. So , there can be energy but no force and power.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.