Gravitational Force Lab

     The purpose of this lab has three parts. The first purpose of the lab consists of learning how to calculate gravitational force in Vpython. The second purpose of this lab is to set up the framework for a future lab that involves modeling planetary and orbital motions. The third purpose is to use arrows in modeling the scale and direction of a vector quantities such as force.

     For the first part of the lab, the program will use two objects and one of the two objects will change position. The gravitational force equation will also be used.

 

 The following is the program code that prints the gravitational force on the smaller object. Following the code, there is a video of the program being run and the print statements of gravitational force with respect to position.

 #Physics 4A Lab: Gravitational Force Lab

#April 11th 2012
#Chris Cosio
#This is a program to similate gravitational forces between two or more objects
from __future__ import division
from visual import*

t=-1
G=6.7e-11 #Gravitational Constatnt
mcraft=15e3 #mass of spacecraft
mplanet=6e24 #mass of planet
rvector=vector(-13e7,6.5e7,0) #initail position of spacecraft
deltar=vector(6.5e7,0,0) #change in position

while t<=3:
    t=t+1#counter for loop
    x=t+1#counter for position
    position=rvector+deltar*t#position definition for spacecraft
    planet=sphere(pos=(0,0,0),radius=6.4e6,color=color.blue) #Planet
    spacecraft=sphere(pos=position,radius=4e6, color=color.orange)#Spacecraft
    r=spacecraft.pos-planet.pos #position vector for spacecraft
    rmag=mag(r)#magnitude of vector r
    F_grav_mag=G*mcraft*mplanet/(rmag**2) #Magnitude of gravitational force
    rhat=r/rmag #Unit vector in the direction of position vector r
    F_grav=-F_grav_mag*rhat#Gravitational force vector
    grav_force_mag=mag(F_grav)
    scalefactor=3e4#scale factor to shrink or enlarge arrow
    arrow(pos=spacecraft.pos,axis=-grav_force_mag*rhat*scalefactor, color=color.yellow)#force

              vector(approximate)

    print('Position', x)
    print('Gravitational Force =',F_grav)
    print ('Magnitude of Gravitational Force =',grav_force_mag )
print('done')

     From the code and the video, it can be seen the purposes two and three have been accomplished. The video depicts the gravitational force acting on the smaller (orange) object. If the object had statements to update the position, it would be possible to model the motion of the object due to gravitational forces. Furthermore, the arrows placed on the orange spheres indicate the direction and approximate size of the net force acting on the sphere. These arrows could be used to also model velocity, acceleration and momentum for the sphere if it had been moving.