Incompressibility of liquids
Students are observers. As students walk into the classroom I will fill a few bottles with water (80-90% full). I will hit the top of each bottle. The only effect on the bottle will be that the bottom "falls" out of it. I do not explain anything to the students. After the demonstration I have the students discuss what they think happened.
- Simple hydraulics: that water (and other liquids) do not compress when a force is applied at the open end of a system that is closed at the other end.
- The transfer of energy: The energy created from the mallet striking the bottle compresses the air. The compressed air pushes on the water. Because the water is incompressible the energy is converted into a shock wave that travels through the water and strikes the bottom of the bottle, causing it to break.
- Critical thinking skills are developed. The students must reason amongst each other what happened.
- The vocabulary that will be introduced after this lesson will vary, depending on how it is presented, as either an introduction to hydraulics or the conservation of or transfer of energy.
- Hydraulics Vocabulary: Hydraulics and Pressure
- The concept derived will be Pascal's Principle, that any change in the pressure applied to an enclosed fluid is transferred through all parts of the fluid and the enclosing walls without any loss of energy.
Context for Use
Resource Type: Activities:Lab Activity, Classroom Activity:Short Activity:Demonstration, Activities:Classroom Activity
Grade Level: High School (9-12)
Description and Teaching Materials
- A couple of beer or wine cooler bottles (remove the labels)
- Rubber mallet
- Safety goggles
- A glove
Teaching Notes and Tips
Grade 9-12 Strand II Physical Science Substrand D: The student will use Newton's three laws of motion to qualitatively and quantitatively describe the interactions of objects.