Radiation Pressure: The Feel of Photons
How much “impact” does light have when it hits your body?Copyright 2014 Casey Muir-Taylor, CC BY-SA.2.0, Flickr, https://www.flickr.com/photos/121483302@N02/15658166949
Students take an illuminance reading of a light, find a way to approximate it at as an intensity reading, and then calculate the photon flux and radiation pressure while assessing the precision of these values. The ideas are then applied to speculate about engineering challenges involved in using ground-based lasers to propel interstellar spacecraft. In the process students must work through challenging problem solving and analyze the confidence in their results. There is also emphasis on comparing and contrasting the scientific method to the engineering design process.
Light exerts force so it can accelerate things, even spacecraft. Engineers at the Breakthrough Starshot project are tackling a host of engineering problems to use lasers to send spacecraft to one of the closest stars outside our Solar System, Alpha Centauri. Students are given the task of engineering a viable process for converting from illuminance to intensity. After reflecting on the role of engineering in that work, they pick some of the problems engineers on the Breakthrough Starshot project wrestle with, like how to hit a tiny spacecraft in orbit with a laser fired from the ground, or how to keep the mass of the spacecraft low while allowing it to carry the instrumentation needed to explore the Alpha Centauri system. Students then brainstorm their own solutions.
After this activity, students should be able to:
- Demonstrate resourcefulness when working on challenging, open-ended questions.
- Calculate radiation pressure and photon flux from electromagnetic intensity.
- Compare and contrast the scientific method to the engineering design process.
- Use rounding to express a numerical result with optimal confidence.