Question

how to solve the curvilinear motion in rocket

Answer 1

General Curvilinear Motion

Curvilinear motion is defined as motion that occurs when a particle travels along a curved path. The curved path can be in two dimensions or in three dimensions. This type of motion is more complex than rectilinear motion.

Three-dimensional curvilinear motion describes the most general case of motion for a particle.

To find the velocity and acceleration of a particle experiencing curvilinear motion one only needs to know the position of the particle as a function of time.

Let’s say we are given the position of a particle P in three-dimensional Cartesian (x,y,z) coordinates



The velocity of the particle P is given by




The acceleration of the particle P is given by




if we know the position of a particle as a function of time, it is a fairly simple exercise to find the velocity and acceleration. You simply take the first derivative to find the velocity and the second derivative to find the acceleration.


The magnitude of the velocity of particle P is given by


The magnitude of the acceleration of particle P is given by

Note that the direction of velocity of the particle P is always tangent to the curveBut the direction of acceleration is generally tangent to the curve.

However, the acceleration component tangent to the curve is equal to the time derivative of the magnitude of velocity of the particle P In other words, if v_t is the magnitude of the particle velocity (tangent to the curve), the acceleration component of the particle tangent to the curve (a_t) is simply



In addition, the acceleration component normal to the curve is given by



where R is the radius of curvature of the curve at a given point on the curve (x_p,y_p,z_p).

The figure below illustrates the acceleration components a_t and a_n at a given point on the curve (x_p,y_p,z_p).  
the specific case where the path of the blue curve is given by y = f(x)(two-dimensional motion), the radius of curvature R is given by



where |x| means the “absolute value” of x. For example, |-2.5| = 2.5, and |3.1| = 3.1.

However, it is usually not necessary to know the radius of curvature Ralong a curve. But nonetheless, it is informative to understand it on the basis of its relationship to the normal acceleration (a_n).


Curvilinear Motion In Polar Coordinates

It is sometimes convenient to express the planar motion of a particle in terms of polar coordinates (R,?), so that we can explicitly determine the velocity and acceleration of the particle in the radial and circumferential . For this type of motion, a particle is only allowed to move along the radial R-direction for a given angle ?.

we can derive a general equation for its radial velocity (v_r), radial acceleration (a_r), circumferential velocity (v_c), and circumferential acceleration (a_c).

Note that the circumferential direction is perpendicular to the radial direction.
The position of the particle P is given with respect to time, where




To find the velocity, take the first derivative of x(t) and y(t) with respect to time:




To find the acceleration, take the second derivative of x(t) and y(t) with respect to time:




Without loss of generality we can evaluate the velocities and accelerations at angle ? = 0, knowing that radial velocity and radial acceleration is in the x-direction, and circumferential velocity and circumferential acceleration is in the y-direction.



The term d?/dt is called angular velocity. It has units of rad/s. One rad (radian) = 57.296 degrees.

The term d²?/dt² is called angular acceleration. It has units of rad/s².


Since v_r and v_c are perpendicular to each other, the magnitude of the velocity of particle P is given by




Since a_r and a_c are perpendicular to each other, the magnitude of the acceleration of particle P is given by