- #1
Antonio Lao
- 1,440
- 1
Is force the cause of motion? If there is motion would there be a force also?
Newton's 1st law of motion says there can be motion even without force. This motion is a constant velocity (in particular such as the constant speed of light in vacuum).
Newton's 2nd law of motion says that the force is proportional to the acceleration with the mass as the constant of proportionality. But if the acceleration is constant then the force is constant for a constant mass system. Constant force is a conservative force. It's time rate of change is always zero.
If the acceleration is taken to be the constant of proportionality and that mass varies then force can be defined proportionally to the mass with the acceleration as the constant of proportionality.
There seem to be two kinds of force implied in Newton's 2nd law of motion depending whether mass or acceleration is taken to be the constant of proportionality.
If both mass (m) and acceleration (a) are not constant then we get
[tex] \frac {dF}{dt} = m \frac {da}{dt} + a \frac {dm}{dt} [/tex]
In the science of rocketry, this equation is taken into consideration.
Newton's 1st law of motion says there can be motion even without force. This motion is a constant velocity (in particular such as the constant speed of light in vacuum).
Newton's 2nd law of motion says that the force is proportional to the acceleration with the mass as the constant of proportionality. But if the acceleration is constant then the force is constant for a constant mass system. Constant force is a conservative force. It's time rate of change is always zero.
If the acceleration is taken to be the constant of proportionality and that mass varies then force can be defined proportionally to the mass with the acceleration as the constant of proportionality.
There seem to be two kinds of force implied in Newton's 2nd law of motion depending whether mass or acceleration is taken to be the constant of proportionality.
If both mass (m) and acceleration (a) are not constant then we get
[tex] \frac {dF}{dt} = m \frac {da}{dt} + a \frac {dm}{dt} [/tex]
In the science of rocketry, this equation is taken into consideration.