1. William Badders, L.J.Bethel, V. Fu, D. Peck C. Summers,
Discovery Works
(Boston, MA: Houghton Mifflin, 2000) 58.
2. Badders, 59.
3. Badders, 65.
4. Badders, 67.
5. Badders, 89 - 91.
6.
The New Book of Knowledge
(Danbury, CT: Grolier, 1999) Volume 7.
7. www.curtin.edu.au/curtin/dept/phys-sci/gravity/history
8.
The New Book of Knowledge,
Volume 7.
9.
The New Book of Knowledge,
Volume 7.
10. www. Tpt.org/newtons/12/gravity.html
11. www.howthingswork.com
12. Badders, 32 - 34
13. Science Explorer,
Motion, Forces and Energy
( Needham, MA: Prentice Hall,2000) 64-65.
14. Note: Ideas for lesson plans came from askERIC, Discovery Works, and Glencoe Physical Science.