summer_2019:gravitation [Integrating Computation Across the Mitten]

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**Follow this link for the activity and the instructions: [[https://trinket.io/library/trinkets/4b1a7a7441|link]]**

**Or, read the instructions after the image below, and copy the code into your own GlowScript file.**

You should see something that looks like this:

{{ satellite_trinket_screenshot.png?800 | trinket screenshot}}

If you click on the "Instructions" tab in the upper right, a set of instructions for the activity should pop up. Click between "Instructions" and "Result" to alternately view the instructions and the animation. If you prefer, the same instructions are also listed below.

1. Run the code and see what happens! You should see a satellite shooting off into space, completely unaffected by gravity.

2. Read the code, and try to understand how each line is impacting the animation. If you're not sure, try changing the line, and see what happens. Keep track of what you find by writing comments. (Use the # character.)

3. Try using your physics knowledge to fix the code so that gravitational force is being applied correctly.

4. **Extra**: Uncomment (take away the # characters) from the chunks of code marked 'Extra'. Try to fix the graphs so that they correctly display the energy of the satellite. Try to add another curve to the graph that tracks the satellite's total energy.

5. **Extra Extra**: Uncomment from the chunks of code marked 'Extra Extra'. Try to use it to help you create a net force arrow that updates as the satellite moves. Now you have a living, changing, free-body diagram! Try to add another arrow that models the updating satellite momentum.

For more information on glowscript tools, check out: [[https://www.glowscript.org/docs/GlowScriptDocs/index.html]]

<code>
GlowScript 2.7 VPython

# Window setup
scene.width = 600 
scene.height = 400

# Objects
Earth = sphere(pos=vec(0, 0, 0), radius=6.4e6, texture=textures.earth)
Satellite = sphere(pos=vec(7 * Earth.radius, 0, 0), radius=1e6, color=color.red, make_trail=True)

# Parameters and Initial Conditions
G = 6.7e-11
mEarth = 6e24
mSatellite = 20
pSatellite = vector(0, 50000, 0)

# Time and time step
t = 0
tFinal = 1 * 60 * 60 * 24     # 1 day
dt = 1

############################# Extra ##############################
## energyGraph = graph(xtitle='time (s)', ytitle='energy (J)')  ##
## kineticGraph = gcurve(color=color.green, label='kinetic')    ##
## potentialGraph = gcurve(color=color.blue, label='potential') ##
##################################################################


################################# Extra Extra ###################################
## FnetArrow = arrow(pos=Satellite.pos, axis=vec(0, 0, 0), color=color.yellow) ##
#################################################################################


# Calculation Loop
while t < tFinal:
    rate(10000)

    Fnet = vec(0, 0, 0)

    pSatellite = pSatellite + Fnet * dt
    Satellite.pos = Satellite.pos + (pSatellite / mSatellite) * dt

    t = t + dt
  
    ############ Extra ############
    ## kineticGraph.plot(t, 0)   ##
    ## potentialGraph.plot(t, 0) ##
    ###############################
  
  
    ########### Extra Extra ###########
    ## FnetArrow.pos = vec(0, 0, 0)  ##
    ## FnetArrow.axis = vec(0, 0, 0) ##
    ###################################

    
    # Earth Rotation (just for fun!)
    theta = 2 * pi * dt / tFinal
    Earth.rotate(angle=theta, axis=vec(0, 1, 0), origin=Earth.pos)
</code>