Elephants and Ice Skates

Lesson Plans on February 21 2014


Here’s an idea for PBL that a high school class may enjoy.

Which case would apply more pressure on a floor — an elephant standing on its hind legs or an Olympic figure skater standing on both skates?

The imagery is startling and almost comical — perfect for an inquisitive teenager busy analyzing the surrounding world.  Over 10,000 pounds of the largest land animal on Earth balancing itself on its hind legs must certainly press down with more pressure than a mere (approximately) 150 pound-person standing solidly on both skates.

Challenge your students to collaborate in a Google Doc to develop a list of questions they would need to know the answers to in order to solve the final problem.  For example:

  • What is the formula for pressure?

  • How much does an elephant/figure skater weigh?

  • What is the bottom surface area of an elephant’s foot/skate’s blade (which touches the ice)?

Stand back to be available for consultation if needed, but let them work it out.  All the information is freely available. Their findings and calculations can be posted in an Edmodo poll and let their peers vote on which answer is correct and reply with arguments supporting or contradicting the calculations. The calculations will be made over and over again as they discover more details about how skate blades are shaped.

They might want to take a field trip to the ice rink to make an impression of their skate blades on a piece of paper or invite a physicist to a Google Hangout to “visit” the class and discuss the theories offered to explain how skates slide on the ice or design an Algodoo experiment to demonstrate force and pressure.

Students can then express what they’ve learned in a video (using an app such as Educreations) or a digital story (using an app such as Pixntell) or any of a variety of other formats.  Images for the presentation can even be drawn using Skitch or collaboratively in a Google Drawing.  This can also be a good opportunity to discuss digital citizenship and an advanced Internet search to find open-source images.

(You might be surprised to know that 10,000 lbs/(8in x 9.5in x 2 feet) equals approximately 21 lbs/sq.in. whereas 150 lbs/(12in x 3/16in x 2 skates) equals approximately 33.3 lbs/sq.in.  If we would imagine the figure skater in a pirouette on the tip of a single skate, the pressure shoots up to over 4,000 lbs/sq.in.!)

Photo Credits:

Elephant:  http://www.caseyresearch.com/live-assets/images/lp/bt/elephant_standing.jpg
Russian Evgeni Plushenko: http://en.wikipedia.org/wiki/File:PLUSHENKO_EC_2005.jpg