Register to reply

Energy dependence on observer framework

by hokhani
Tags: dependence, energy, framework, observer
Share this thread:
hokhani
#1
Jun13-14, 12:33 PM
P: 272
Does mechanical energy of a system depend on the framework of an observer (neglecting a constant)?
Phys.Org News Partner Physics news on Phys.org
UCI team is first to capture motion of single molecule in real time
And so they beat on, flagella against the cantilever
Tandem microwave destroys hazmat, disinfects
Nugatory
#2
Jun13-14, 01:28 PM
Mentor
P: 3,949
Quote Quote by hokhani View Post
Does mechanical energy of a system depend on the framework of an observer (neglecting a constant)?
Yes. The kinetic energy of a bullet is zero in the frame of an observer who is at rest relative to the bullet, non-zero for an observer who is at rest relative to the target of the bullet.
HallsofIvy
#3
Jun13-14, 02:37 PM
Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 39,682
I agree with Nugatory but I can't help but wonder what you mean by "neglecting a constant".

hokhani
#4
Jun15-14, 02:57 AM
P: 272
Energy dependence on observer framework

Quote Quote by HallsofIvy View Post
I agree with Nugatory but I can't help but wonder what you mean by "neglecting a constant".
Ok, Right. The statement "neglecting a constant" is my mistake.
I clarify my purpose of the question:
Newton's laws are only valid in inertial framework. I like to know whether energy formalism is valid in non-inertial framework or not? In other words, can one solve the problems exactly, using conservation of energy in non-inertial framework?
mattt
#5
Jun15-14, 05:29 AM
P: 127
Quote Quote by hokhani View Post
Ok, Right. The statement "neglecting a constant" is my mistake.
I clarify my purpose of the question:
Newton's laws are only valid in inertial framework. I like to know whether energy formalism is valid in non-inertial framework or not? In other words, can one solve the problems exactly, using conservation of energy in non-inertial framework?

[itex]\int_{t_0}^{t_1}\vec{F}(t)\cdot\vec{v}(t)dt = \frac{1}{2}m v^2(t_1) - \frac{1}{2}m v^2(t_0)[/itex] is valid in frames where [itex]\vec{F}(t) = m \frac{d\vec{v}(t)}{dt}[/itex]

That is, in inertial frames.

You still can use it in non-inertial frames IF you add "inertial forces".


[itex]\int_{t_0}^{t_1}\vec{F}(t)\cdot\vec{v}(t)dt = U(x(t_0),y(t_0),z(t_0))- U(x(t_1),y(t_1),z(t_1))[/itex] is valid in any frame where [itex]\vec{F}(x,y,z) = -\nabla U(x,y,z)[/itex]

where [itex]U(x,y,z)[/itex] does not vary with time in this frame.


Register to reply

Related Discussions
What is the minimum observer energy? Quantum Physics 3
Kinetic Energy's Dependence General Physics 3
Energy density dependence Introductory Physics Homework 2
Does a T.V. transfer energy to the observer? General Physics 1
Kinetic energy's dependence on velocity. Introductory Physics Homework 1