- #1
tomwilliam2
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My textbook is describing a 3-body situation where there are two large masses rotating around their barycentre, and a third much smaller mass experiencing gravitational forces from the two larger masses. If the frame of reference is the one in which the barycentre is at rest, then it is not inertial. For the smaller mass, there is an angular speed ##\Omega## to take into account.
The gravitational force due to the two masses is clear, but when my textbook sets out the equation of motion for this mass, it just gives the result in this frame of reference as:
$$\mathbf{\ddot{r}} + 2(\mathbf{\Omega \times \cdot{r}})+(\mathbf{\Omega \cdot r})\mathbf{\Omega - \Omega^2 r}=-G\left(\frac{M_1}{r_1^3}\mathbf{r_1} + \frac{M_2}{r_2^3}\mathbf{r_2}\right) + \frac{1}{m}\mathbf{F_d}$$
Without any explanation. I'd like to try and derive it for myself. Any idea how to go about doing that?
Obviously I could start with:
$$\mathbf{\ddot{r}} + \mathbf{\alpha(\Omega)}=-G\left(\frac{M_1}{r_1^3}\mathbf{r_1} + \frac{M_2}{r_2^3}\mathbf{r_2}\right) + \frac{1}{m}\mathbf{F_d}$$
Where ##\alpha## represents the contribution to the acceleration caused by the rotating frame of reference, and ##F_d## is the disturbance forces.
The gravitational force due to the two masses is clear, but when my textbook sets out the equation of motion for this mass, it just gives the result in this frame of reference as:
$$\mathbf{\ddot{r}} + 2(\mathbf{\Omega \times \cdot{r}})+(\mathbf{\Omega \cdot r})\mathbf{\Omega - \Omega^2 r}=-G\left(\frac{M_1}{r_1^3}\mathbf{r_1} + \frac{M_2}{r_2^3}\mathbf{r_2}\right) + \frac{1}{m}\mathbf{F_d}$$
Without any explanation. I'd like to try and derive it for myself. Any idea how to go about doing that?
Obviously I could start with:
$$\mathbf{\ddot{r}} + \mathbf{\alpha(\Omega)}=-G\left(\frac{M_1}{r_1^3}\mathbf{r_1} + \frac{M_2}{r_2^3}\mathbf{r_2}\right) + \frac{1}{m}\mathbf{F_d}$$
Where ##\alpha## represents the contribution to the acceleration caused by the rotating frame of reference, and ##F_d## is the disturbance forces.
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