Skewered Balloon (Andrew Salg)
Author
Andrew Salg
Principle(s) Illustrated
Interaction between two objects
Molecular structure of objects
Standards
HS-PS2-3. Apply scientific and engineering ideas to design, evaluate, and refine a device that minimizes the force on a macroscopic object during a collision.
HS-PS2-6. Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
Questioning Script
Materials Needed:
1 metal or wooden skewer
1 balloon
Vegetable Oil
Prior knowledge & experience:
The students will need to know about the structure of objects, and how the design of an object can effect how its durability. Students should also know what polymers are, and how they are used in everyday life. Some basic knowledge on molecular structure is also required to understand how chains of molecules matter in creating tools and other objects that we use.
Root question:
What will happen to the balloon when the wooden skewer is pushed through the balloon?
Target response:
The skewer will be able to pass through the balloon. The most important part is to pierce the balloon at the points that are leased stretched. Long polymer chains are interconnected to one another. The bigger the balloon the more that these chains are stretched to their breaking points. To demonstrate try pushing the skewer through the sides of a balloon.
The motion of twisting instead of jabbing the balloon while holding the skewer is also important. The twisting helps to manipulate the structure of the polymers that make the balloon. The polymers form essentially a net to help hold in air, when that net is enacted upon in a way that it was not designed to handle. In this case latex has a design that instantly breaks when stabbed, but breaks apart while not popping while being twisted.
The lubricant being used also helps to create less friction while pushing and twisting. The lubricant (canola oil or petroleum jelly) can also help cover parts of the skewer that may be slightly warped or uneven in some cases.The amount of force is also a factor because with too much force will burst the balloon. Pushing in to much while twisting will cause an instant popping of the balloon. However, with the lubricant and twisting can help slowly push the skewer through without popping the balloon.
Common Misconceptions:
Most students will think that the balloon will pop. This can be true if not done correctly, but for the most part the skewer can pass through the balloon. The students assume that by taking a sharp object to a thin polymer that the balloon will instantly pop.