Incompressibility of liquids
Summary
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.
Learning Goals
The concepts that the students are to learn are:
- 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
This discrepant event is best used to introduce the section on hydraulic force. This could be used at lower levels, but fits nicely in 9th grade physical science or in physics class. It's a quick demo. All you need is a couple of beer or wine cooler bottles (remove the labels), a rubber mallet, safety goggles, a glove, and a wastebasket.
Description and Teaching Materials
Materials:
- A couple of beer or wine cooler bottles (remove the labels)
- Rubber mallet
- Safety goggles
- A glove
- Wastebasket
Teaching Notes and Tips
Assessment
The assessment is done while the students are discussing what happened. A better assessment leads into the lesson on hydraulics when they can apply the event to what we are studying.
Standards
Grade 9-12 Strand II Physical Science Substrand C: The student will understand energy forms, transformations, and transfers.
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.
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.