More Discrepant Events in Science
Posted by David Wetzel
Science Discrepant Events
The following are discrepant events that does not turn out as expected.
These anomalies challenge students’ beliefs and makes them more receptive to learning what you want them to learn.
Alcohol and Water Miscibility: Discrepant Event
Miscibility means how completely two or more liquids dissolve in each other.
Materials Needed per Group: two 50 mL beakers, 0ne 100 mL beaker, 100 mL water, 100 mL ethanol
Students complete the following:
Add 50 mL of water to 50 mL of water. They
Add 50 mL of ethanol to 50 mL of ethanol, you get 100 mL of ethanol.
However, when 50 mL of water is added with 50 mL of ethanol?
They get a 96 mL solution.
Why?
The water and ethanol molecules are different sizes, with the ethanol molecules are smaller. Some of the ethanol fits in the spaces between the water molecules.
Think about two other materials: a liter of sand and a liter of pebbles. If you pour the sand into the pebbles, the total volume will be less than two liters, because some of the sand fills in the spaces between the pebbles.
Bernoulli’s Principle: Discrepant Event
Materials Needed per Group: two empty soda cans, 23 straws, one metric ruler
Students complete the following:
Place 22 straws side-by-side 1 cm apart.
Place the two empty soda cans on the straws 5 cm apart.
Two empty soft drink cans are placed on several drinking straws. Air pressure forces the cans to roll toward each other.
Using the remaining straw, blow between the cans.
The cans roll towards each other until they collide.
Why?
As the velocity of the air between the two cans increases (being blown away), the pressure the air it applies to the inner sides of the cans decreases.
This allows the air on the opposing sides of the cans to push the cans towards to the area of lower pressure.
Ensure students understand that the air pressure on the outer sides did not increase, rather it was the decrease in pressure between the cans that allowed the cans to roll towards each other.
The cans were not “sucked” together. They were pushed together.
Additional Resources
Teaching Science using Discrepant Events
