# physics4me

physicsgg

## Getting the Swing of Surface Gravity

Brian C. Thomas & Matthew Quick
Sports are a popular and effective way to illustrate physics principles.
Baseball in particular presents a number of opportunities to motivate student interest and teach concepts.
Several articles have appeared in this journal on this topic, illustrating a wide variety of areas of physics.
In addition, several websites and an entire book are available.
In this paper we describe a student-designed project that illustrates the relative surface gravity on the Earth, Sun and other solar-system bodies using baseball.
We describe the project and its results here as an example of a simple, fun, and student-driven use of baseball to illustrate an important physics principle.
This project was completed to satisfy a course requirement in an introductory astronomy course at Washburn University (a Masters-level university) in Topeka, Kansas.
The assignment was an open-ended, independent project designed and executed by the student. The requirements were that the project must be self-designed and related to astronomy, with creativity emphasized.
The project described here asks the question “What would it be like to play baseball on other
planets?” Two quantities were chosen for comparison: “hang time” of the baseball and distance from home plate to the center field fence.
These values are affected by the surface gravity of the planet or other body.
Surface gravity means the gravitational acceleration at the surface of the body, which depends on both the body’s mass and the distance from the center to the surface.
We realize that one would not actually be able to stand (let alone play baseball!) on the surface of a planet such as Jupiter; the idea is to help students understand surface gravity. This concept may be difficult for some students, since it involves variation of two parameters simultaneously.
Therefore, we hope this exercise will be both engaging and useful in helping students understand the counter-intuitive fact that even a planet with greater mass than the Earth (for instance, Neptune) may have a smaller surface gravity, or vice versa…..