Joy Burton, Science Teacher @ Sutter Middle School
- Polymers as molecules and chains
- Space between molecules
- Properties of polymer cross-links
- Properties of balloons
Balloons are made of a rubber latex polymer made of long chain-like molecules, or strands, that are all snarled together with bonds between the strands, called cross-links. Cross-linked molecule networks can be stretched.
Cross-linking occurs when molecules of a polymer are chemically fixed to each other. These links hold the polymer molecules together and allow them to stretch…up to a degree. When the force or tension pulling on the cross-links is too great, the polymer will pull apart and break.
When the balloon is filled with air, the rubber, at the ends of the balloon is stretched out less than in the middle of the balloon. Therefore, there is less force pulling on it. This allows the tip of the skewer to break some polymer cross-links, push aside the molecules of rubber, and slide into the balloon.
A balloon that is made of thin sheets of rubber latex and filled with air can be penetrated and not popped with a needle. This is due to the many intertwined strands of polymer molecules that make up the rubber latex. The tied end and the nipple end of the balloon is the best area to insert the needle, because the polymer strands stretch around the needle. However, if the needle is inserted where the balloon is tightly stretched, the balloon will pop. It does help if the skewer is coated with lubricant, such as mineral oil.
Properties of Matter
Each of the more than 100 elements of matter has distinct properties and a distinct atomic structure. All forms of matter are composed of one or more of the elements. As a basis for understanding this concept:
- a. Students know the structure of the atom and know it is composed of protons, neutrons, and electrons.
- b. Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements.
- c. Students know atoms and molecules form solids by building up repeating patterns, such as the crystal structure of NaCl or long-chain polymers.
- d. Students know the states of matter (solid, liquid, gas) depend on molecular motion.
- e. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently.
Prior knowledge & experience:
Middle school students know that balloons expand, are made of rubber, can increase a balloon's size by adding gases and/or liquids. They also know that excessive amounts of gases or liquids, as well as sharp objects could cause balloons to pop. They know that helium balloons will float (rise), whereas balloons filled with water and air will not float. Some know that rubber balloons are swallowed by ocean animals which causes the animal to feel full causing the animals to starve.
1. What would happen if a needle is inserted into a balloon filled with air?
2. If the balloon does not pop why does this happen?
3. What would happen if a needle is inserted into a balloon filled with air?
4. If the balloon does not pop why doesn't the balloon pop?
5. What is the purpose of the oil?
6. What happens when the balloon is pierced on the side and not at the ends
7. What would happen if a different kind of skewer is used?
8. What would happen if a different kind of balloon is used?
As the skewer/needle is slowly pushed with soft gentle pressure through the balloon, the first thought would be that the balloon would pop. Even though the atoms of the rubber latex of the balloon are closely locked in position, the balloon surface is impenetrable. No two objects can occupy the same space at the same time.
A common misconception of students about balloons is the idea that balloons and needles do not mix. A needle will pop an inflated balloon.
Photographs and Movies
Skewer Through Balloon - Cool Science Experiment - YouTube
California State Science Standards