Ask what would happen if they stopped pushing. Have a third student gently pull down on the arch-makers' arms to test the strength of the arch. Ask two more students to join the arch. Invite the group to brainstorm ways for the two new members to make the arch stronger. Test each suggestion with the same person pulling down each time.
Additional Challenges Ask why it is important to have the same person pull on the arch each time.
Credits Excerpted from Building Big Activity Guide. Building Big is a PBS television series exploring the world's greatest engineering feats. Funded by The National Science Foundation, National Endowment for the Humanities, The Arthur Vining Davis Foundations, the Corporation for Public Broadcasting, public television viewers, the American Society of Civil Engineers and Siemens.