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Portrayal of Physics in Gravity - A Film Review

## Portrayal of Physics in the Film

You will watch the film Gravity, directed by Alfonso Cuar´on, and answer several questions about physics topics from this class that appear in the film and about the portrayal of physics topics in popular culture from the perspective of this film.

As you watch the film, take note of how physics appears in the film, particularly any unrealistic physics or errors in physics. Some of these may overlap with aspects of physics discussed in the sections below. Write an essay describing the instances of unrealistic or erroneous physics that you noticed and how they may have been important to the plot. The film had science advisors; explain why you think the filmmakers may have decided to alter the physics for the film. Support your arguments with physics you have learned in this class. Your discussion should be qualitative, but you may make quantitative arguments if you like. This section is expected to be 250-500 words.

Answer one of the following questions. Write your answer in essay form, including any necessary mathematics or formulae. Give quantitative answers as requested in each question.

1. From about 0:19:10 to 0:19:22, astronaut Kowalski gives some information about the orbit of the space debris that plays an important role in the film. First, is the 50,000 mile/hour debris speed realistic if the debris is in a closed orbit around the earth (compare to escape velocity)? Ignoring that issue, give some characteristics of a possible realistic orbit for the debris. It should intersect the orbits of the Hubble Space Telescope (where the movie begins) and International Space Station approximately every 90 minutes.

2. At one point, astronaut Stone is stuck in a damaged Soyuz capsule and needs to reach the Chinese Tiangong-1 space station (which was in orbit when the movie was filmed). Assume that the Soyuz is in approximately the orbit of the International Space Station. The Tiangong is in a lower orbit, and the Soyuz and Tiangong are separated by an angle of about 120? around the center of the earth. At approximately 1:10:00, Stone fires rockets on the Soyuz. Do the rockets need to fire in the same or opposite direction of Soyuz’s orbit around the earth? Estimate how the rockets can change the velocity of the Soyuz capsule so that it will approach the Tiangong.

3. Accelerating Reference Frame

Answer one of the following questions. Write your answer in essay form, including any necessary mathematics or formulae. Give quantitative answers as requested in each question.

## Orbital Mechanics

A) At approximately 0:32:00, astronauts Stone and Kowalksi are attached to the International Space Station by a cable. Kowalski lets go of the cable and drifts off fairly quickly. Estimate how far Kowalski is from the space station before he lets go (by measuring distances on the screen) and also how quickly he drifts away (this may be more difficult, but you can try to use perspective). Assume that he flies away due to centrifugal force because the space station is rotating. What must the angular velocity of the space station be to give an appropriate acceleration? (Kowalski should actually drift away due to being in a slightly different orbit than the space station, but that should only be a few meters per minute.)

B) At about 0:52:20, astronaut Stone is trying to detach a Soyuz capsule from a cable that is holding it to the International Space Station when debris hits the station. This causes the Soyuz capsule (and Stone) to start spinning around the station because it is attached to the cable (this lasts about 40 seconds). Estimate the length of the cable and speed of the Soyuz capsule’s rotation around the space station. Based on that, estimate the fictitious forces acting on the Soyuz and Stone and compare the corresponding accelerations to g (the acceleration due to gravity on earth).

Answer one of the following questions. Write your answer in essay form, including any necessary mathematics or formulae. Give quantitative answers as requested in each question.
At approximately 0:12:26, space shuttle Explorer is struck by space debris and begins rotating. Both questions have to do with the rotation of Explorer in this scene. You may model the shuttle as a triangular lamina attached to a cylinder or rectangular prism to answer your chosen question. Look up space shuttle specifications and apply them to your model to find a moment of inertia tensor you can use in your answer.

1. Estimate the angular velocity of the Explorer when it first starts rotating by counting rotations against the film timer (as best as is possible). Given that the debris hits the space shuttle near the end of a wing, estimate the impulse (see homework assignment 1) that the debris must impart to the wing of the Explorer to make it rotate that fast.

2. Assuming the Explorer starts rotating entirely around its long axis, use the Euler equations to find how it rotates as time passes. Specifically, does its angular velocity gain a large component around one of the other principal axes and, if so, which becomes significant first? Does the film portray the rotation of the space shuttle accurately?