Black Holes and Gravity

Overview: The concept of gravity is a difficult one for many physical science students to master.  Preconceived ideas of what gravity is and how it works can interfere with new material presented to students.

Purpose: Framing a discussion of gravity in the stars removes the student from their familiar background of "what goes up must come down".  These activities will help students to approach the concept of gravity from a fresh viewpoint.

Objectives: Through this discussion, students will be able to:
    a) Understand the basic concept of gravity as a force.
    b) Give the mathematical relationship between the force of gravity, the mass of the objects involved, and the distance between them.
    c) Describe the basics of what black holes are and how they form.
    d) Explain how the massive size and density of the black hole can result in an event horizon.

Resource materials:
    1. Images of galaxies and black hole systems from WIRO, RBO or similar observatories.
    2. Computer lab with internet to conduct searches.
    3. Board games and pieces printed out for class from NASA's website, listed in links.
    4. Large sheet of rubber, marbles and 1kg of steel bearings for "bending space-time".

Activities:
    1. Show galaxy images and have students hypothesize what is at the center. Discuss galaxy composition.
    2. Have students write a paragraph describing what they think a black hole looks like, and what it would be like to go near one.
    3. Reviews these and discuss misconceptions.
    4. Have students conduct an internet scavenger hunt to find the basics of black holes and gravity.
    5. Perform "bending space-time" demonstration listed below.
    6. Finish the activity with some fun by playing NASA's "Fall Into A Black Hole".

*Bending Space-time*
    1. Have students stand around the sheet of rubber, pulling it taught. Warn them not to let go.
    2. Roll a marble across the surface of the rubber.
    3. Pour the steel bearings on the sheet to represent stardust.  They should aggregate in the center, bending our "space-time".
    4. Again roll the marble across the sheet, and discuss why the path is different, and how this relates to gravity.
    5. Allow students who are not holding the fabric of space-time to roll marbles, each marble should end in the middle.
    6. Discuss how a black hole would look on our sheet.

Useful Links:

Black Hole Scavenger Hunt

NASA's "Fall Into A Black Hole!" game site