Watermelon Explosion

How to Make a Watermelon Explode with Only Rubber Bands

Kristen Strecker

Abstract

The purpose of this experiment is to determine if rubber bands could place enough pressure on a watermelon to make it explode.  The experiment demonstrates compression, kinetic and potential energy.  The method will be putting as many rubber bands around the middle of the watermelon until it explodes.  The watermelon’s top will pop after placing 600 or more rubber bands around the middle.  This is a deliciously spectacular summer stem activity.  It provides an opportunity to discuss and demonstrate some new scientific terms and it is a lesson that patience and persistence pays off with great reward.

Introduction

I first saw this demonstration on The Slow Mo Guys YouTube channel.  The original airdate was July 18, 2012.  I have since done it three times with my family and friends.  We even made it a part of our summer vacation to Florida.  The materials are easy to obtain and inexpensive. It has been my experience that before the age of 6 the little ones may not have the attention span needed to complete the experiment.  Ages 6 and above are very interested in doing the work needed to see results.  It will take approximately 30 min to complete depending on determination of participants.

Materials

Watermelon

Sharpie

600 or more Rubber Bands

Bowl

Sturdy surface outside

Methods

1. Obtain a watermelon small or medium.  In this case bigger isn’t better.

• Children can use a sharpie to decorate the watermelon if desired.

• Place watermelon on a steady surface outside using a small bowl as a base.   By placing the watermelon into the bowl it will be prevented from rolling and the bowl will keep it upright so rubber bands can be placed with ease.   It is suggested to do this experiment in an area that is easy to clean outside.  This will get messy!

• Letting each child make estimates of how many rubber bands it will take to make the watermelon crack is a great way to keep kids interest in the process.

• Start placing rubber bands in the center of the watermelon continue placing them as close to center as possible.  The best method is for two people to grab the rubber band with both hands and stretch it to a size greater than the diameter of the watermelon and lower it down to the middle before letting go. 

This is a lengthy process many moans and groans are possible but with focus comes reward. The watermelon will change shape during the process.  Bulges will form around the rubber bands making note of the changes and discussing some of the science terms found in the glossary below will be a great way to pass the time.

A crack will form near the top moments before it explodes so stand back and enjoy the show.

• Eat up and clean up!  The bottom of the watermelon should remain clean and edible if all goes well.  Clean up can be made fun by telling the children to gather the pieces of the rind and try to place the watermelon back together again. 

Another cool part of this demonstration is chasing down the rubber band ball that forms when the watermelon finally gives way.  After the kids are done playing with it I undo the ball and put them in a full sink of soapy water to wash them and lay them out to dry in order to put them to everyday use or to explode another watermelon we may happen upon.

Results

The watermelon exploded after approximately 30 minutes.  The children placed 600 rubber bands of various sizes around the middle of the watermelon.  The rubber band ball landed approximately 3 yards away from the watermelon stand.  Juice and fruit splattered all over the blast sight including the delighted children. 

Discussion

Exploding a watermelon is one of the greatest summer learning activities of all time. It brings the concepts of kinetic and potential energy to life for young minds. This experiment provides many opportunities for conversations about scientific concepts as simple as defining solids, liquids and gases or the more complex concepts compression and tensile strength.  Just by hearing scientific terms early on will give the terms a familiarity later in the kids education that decreases the intimidation sometimes is associated with science in little ones.  Doing fun easy experiments drive curiosity and gives kids confidence in their ability to do science. 

Glossary of simplified terms

Force- An action that causes an object to keep its shape or change shape.

Deformation- To cause a change in shape.

Elastic deformation- To change shape and then return to original shape if force is removed.

Inelastic deformation- Changes shape and does not return to original shape if force is removed.

Kinetic energy- Energy of movement

Potential energy– Stored energy

Compression-Pressure on liquids

Tensile strength– The maximum amount of force an object can take before it breaks.

Dynamic equilibrium- Balance

Pressure- Continuous physical contact or pushing against on object.

Bifurcation- Dividing something into two parts.