Monthly Archives: May 2012

the physics of momentum flings

One of the main mechanics in Portal 2 is the momentum fling, which allows a player to send themselves great distances through the air. A momentum fling redirects momentum gained through potential energy into a parabolic path through the air. It involves two portals, one placed well below a player and another usually placed on a vertical or angled panel. Whatever momentum a player gains going into the portal below them will be conserved as they are flung out of the vertical or angled portal and then fly through the air.

A few things to note:

1) The player flies farther than the companion cube. The player doesn’t feel air resistance while the cube does. Also, it appears that the player lands exactly where the equations say she should (of course, slight approximations were involved, so a little more detailed experimentation would be a good thing). +1 for the Source engine’s accuracy.

2) In class, the momentum fling can be used to investigate multiple areas of physics, including: momentum, conservation of energy, projectile motion, and air resistance. All great physics topics.

3) Adding barriers or obstacles would make this a perfect way to test student knowledge of projectile motion. Give students a maximum ceiling height or a minimum path height (i.e. a wall is between the player and the destination) and allow students to calculate the necessary starting height and portal angle to make it to their destination.

4) Add a moving target to further torture students. Make them calculate the time it takes to make it to a destination. Now they have to figure out the math to fling themselves not only to the right place but at the right time.

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