Three More Discrepant Events in Science

Observing Events Which Do Not Appear to Follow the Rules of Nature

Sep 11, 2008 David R. Wetzel

Discrepant events are an excellent teaching strategy in science to motivate students who are typically not interested in science and challenging all students. Tapping into a student’s prior knowledge and experiences are the best approach to challenge their curiosity. As students try to make sense of what is happening, they become engaged in the process of their own education.

One discrepant event which can be used to stimulate discussion and mental conflict, which means students are thinking, is to ask how many have ever had a shower curtain move towards them in the shower.

This is an excellent lead in or analogy for Bernoulli’s Principle. The shower water spray creates a low pressure area between the student and a light shower curtain. This causes the shower curtain to move towards them when taking a shower.

Discrepant Events in Science

The following are two more discrepant events which cause students to use their critical thinking skills to explain what they are observing.

Mysteriously Floating Eggs

Materials: three 500 ml beakers or similar glass containers, three raw eggs, tap water, sugar, salt, and stirring rod.

• Mix 75-100 grams of sugar in one beaker of tap water

• Mix 75-100 grams of salt in one beaker of tap water

• Add tap water to third beaker

• Using the beaker of tap water, ask students what they think will happen when the egg is placed in the beaker

• After discussion, place egg in beaker and students observe it sink

• Ask students to explain why the egg sank (answer: egg is denser than water)

• Ask students what they think will happen to an egg placed in salt water

• After discussion, place egg in beaker and students observe it float

• Ask students to explain why the egged floated (answer: salt water is denser than egg)

• Do the same with the sugar water and students observe the egg floats (answer: sugar water is denser than egg)

• Extension: use rubbing alcohol instead of tap water for a fourth test of floating eggs

Mysterious Floating Corks

Materials: for each student group – one clear glass, one small cork, and tap water.

• Students fill glass two thirds full of tap water

• Now they place the cork in the glass of tap water and try to keep it floating in the center

• Ask students if they can keep the cork in the middle and explain what they are observing

• Students observe the cork always moves to the edge of the glass (answer: cork moves to highest water level because it is less dense than water)

• This is excellent for proving the Meniscus effect of liquids in containers

• Ask students what they think will happen to the cork if the class is filled with water

• After discussion, students now add water to the glass so that it creates a bubble of water on top the glass, without overflowing (cork is still in glass)

• Students now observe the cork moves to the center of the glass (answer: the cork moves to the highest point because it is less dense than water and held in place due to surface tension of water)

The use of discrepant events is the best way to motivate the unmotivated student and engage all students to think critically. The use of the materials above are typically within the realm of most students’ personal experiences and knowledge, which makes the mental conflict and resulting better understanding of related science concepts more meaningful for them.

Additional discrepant events and procedures can be viewed by visiting Science Discrepant Events and Critical Thinking .