How To Build A Tennis Ball Mortar

Learning science can be dry and uninteresting unless you apply it in a way that brings the subject to life, like in learning how to build a tennis ball mortar. The "cannon" is easy to construct, takes very little time, and is made from materials easily available everywhere. Before learning how to build a tennis ball mortar, the builder should take a few moments to learn the basics behind how it works. The force used to propel the tennis ball from the barrel is provided by a few drops of lighter fluid. The lighter fluid, when ignited, forms a "ball" of hot gas which is focused on the tennis ball placed on top of it. The baffles in the cans focus the expanding hot gas onto the tennis ball, forcing it out the length of the tubes. Although there are several different methods and materials that can be  used to build a tennis ball mortar, this is the easiest and cheapest.

Materials needed:

  • Three empty Pringles Potato Chip Containers
  • Can opener
  • Duct tape
  • Tennis balls
  • Lighter fluid
  • Barbecue lighter
  • Electric drill and bit 
  • Something solid to lean the mortar against when firing
  • Eye protection and leather gloves
  • Optional – 3" PVC pipe
  1. Using the can opener carefully remove the bottoms from two of the cans. The cans are made of cardboard so take extra care not to crush or deform the tubes.
  2. Wipe the cans out using a damp rag. Care should betaken not to get the containers too wet or the cardboard will swell and deform, causing structural weakness.
  3. The one container with the bottom remaining will be the component. Place one of the containers with the bottom removed onto the top of the bottom container and duct tape into place.
  4. Place the next can on top of the second stage and duct tape into place.
  5. Using the duct tape, completely cover the tube with three to five layers of duct tape. 
  6. At this point, if the builder desires to make the system stronger they can place it inside the 3" PVC pipe. Enough duct tape should be used on the outside of the containers so that it fits snugly inside the pipe.
  7. Using the electric drill, place a 1/4" hole in the side of the mortar, 1" from the bottom of the mortar.
  8. The mortar is no ready to fire.

To fire:

  1. Lean the mortar against some kind of  platform for stability angled at about 45 degrees, drilled hole at about the 2 o'clock position
  2. Put on eye protection and gloves.
  3. Squirt 1 and 1/2 tablespoons of  lighter fluid down the mortar,  trying to hit the bottom of the can rather than allowing it to drizzle down the sides..
  4. Drop the tennis ball into the mortar. Form this point on be sure no one is in front of the mortar.
  5. Allow 1-2 minutes for the lighter fluid to begin to evaporate and fill the space below the tennis ball with combustible vapor.
  6. Hold the lighter near the drilled hole, being careful not to place yourself near the mouth of the mortar.

The mortar should fire. For optimum range the mortar can be angled differently, slightly more or less lighter fluid can be used, and the wait time for vaporization can be adjusted. These instructions on how to build a tennis ball mortar are some of the easiest available, but any time fire, combustible materials, and explosions are involved great care must be taken.

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