- #1
greypilgrim
- 547
- 38
Hi.
One of my undergrad professors emphasized explicitly that Newton's second law
$$\mathbf{F}=\frac{d\mathbf{p}}{dt}$$
is not a definition of force, but an empirically found relation between a force law (e.g. Hooke's law) and the change of momentum of an object this force acts upon.
Wikipedia says
The four-force is the four-vector defined as the change in four-momentum over the particle's own time:
$$\mathbf{F}=\frac{d\mathbf{P}}{d\tau} .$$
So what is force in SR, just a definition?
Assume we have a spring with some spring constant that is compressed to half its length and moves at a velocity close to c. How does it act on
One of my undergrad professors emphasized explicitly that Newton's second law
$$\mathbf{F}=\frac{d\mathbf{p}}{dt}$$
is not a definition of force, but an empirically found relation between a force law (e.g. Hooke's law) and the change of momentum of an object this force acts upon.
Wikipedia says
The four-force is the four-vector defined as the change in four-momentum over the particle's own time:
$$\mathbf{F}=\frac{d\mathbf{P}}{d\tau} .$$
So what is force in SR, just a definition?
Assume we have a spring with some spring constant that is compressed to half its length and moves at a velocity close to c. How does it act on
- an object initially in the spring's rest frame (but observed from the lab system)?
- an object initally at rest in the lab system?