Based on the following passage, what force can you infer is responsible for causing an implosion if not pressure?
Implosion is the process of strategically placing explosives at various key points along a building’s main supports. When the explosives are detonated, the key supports fail, the building becomes unstable. The term implosion here is a misnomer; technically an implosion is a difference between the external pressure of a building and its internal pressure that is so great the building collapses on itself.
1. gravity
2. friction
3. air resistance
4. centripetal force