GRADES 1-8
PAPER STRUCTURES

BACKGROUND INFORMATION: There are two general types of motion caused by forces acting on an object. The first, called "translational motion", is the kind of straight motion which is an example of the system falling downward under its weight if it were not balanced by upward forces. The second kind of motion that could result from these same forces is called "rotational motion." Scientists and engineers often summarize the forces in a problem using the "center" of the force. The force is treated as if it acted through a single point. Pressure is a measure of force over an area (Pressure = Force/Area), while the center of gravity refers to the force created by the weight of an object. What exactly does "center of pressure" and "center of gravity" mean? To understand this concept, let's examine another device - the javelin. Modern javelins land "point-down". Earlier javelins either traveled with the point up (which was dangerous) or horizontally. When the javelin landed horizontally in competitions it was difficult to determine the exact landing point. In 1984 the International Amateur Athletic Federation (IAAF) adopted new rules to make sure future javelins were designed to land point-down, so the "touch-down" point would be known exactly. Every javelin designed for competition has the same "center of gravity" or balance point. However, the center of pressure on a javelin remains behind the center of gravity and the direction of the center of pressure is opposite that of the gravitational force. This keeps the javelin's point slanted toward the ground. Center of Pressure Behind the Center of Gravity Javelin Tip Points Down What would happen if the center of pressure was in front of the center of gravity on a javelin? The nose of the javelin would point up. Center of Pressure In Front of the Center of Gravity Javelin Tip Points Up The paper structures you create work in the same manner. The structures collapse when the forces acting on the structure are out of balance.