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Water Jug Puzzle | Air Pressure Trick

Updated on September 29, 2014

Scene from Die Hard With A Vengenance

Scene with the water jugs.
Scene with the water jugs. | Source

Water Jugs Puzzle

This is a fun puzzle with water jugs from the movie, Die Hard With A Vengeance. Bruce Willis and Samuel Jackson play characters that have to follow a bomber's instruction so he does not explode another bomb.

This article was written October 11, 2012.There are 2 water jugs with one that holds 5 gallons and another that holds 3 gallons. In the movie, they have to put exactly 4 gallons of water on a scale to deactivate the bomb. But I will make this more extensive and easier to understand. If you know how to make exactly 1 gallon or 2 gallons then you can combine them to make any amount up to 8 gallons.

Like 1 gallon added to the 3 gallon jug or container would make 4 gallons and 2 gallons added to the 5 gallon jug would make 7 gallons. So how do you measure exactly 1 or 2 gallons. This is where you can stop reading if you want and try to figure it out. There are no tricks in this. It is just addition and subtraction.

By understanding this more thorough version will prepare you for more complex problems. Take the 3 gallon jug and fill it up. Then pour those 3 gallons into the the 5 gallon jug. Then fill up the 3 gallon jug. Pour the water from that into the 5 gallon jug that already has 3 gallons of water in it. So only 2 gallons can go in and that will leave you with exactly 1 gallon.

Note that in science and engineering, exact has no meaning. You need to be given a tolerance. For example this method would not be exact if the tolerance was plus or minus one drop. This would have a tolerance more like plus or minus a half of a fluid ounce. So you can empty out the 5 gallon jug and then pour the 1 gallon into it. Then just fill up the 3 gallon jug and add that to the 1 gallon and you have 4 gallons that was asked of in the movie.

To get 2 gallons, you fill up the 5 gallon jug or container and pour the water into the 3 gallon jug. This leaves you with 2 gallons in the 5 gallon jug. As an alternate solution to the 4 gallons in the movie, you empty the 3 gallon jug and pour the 2 gallons into it. Then fill up the 5 gallon jug and pour the water into the 3 gallon jug that has room for exactly 1 gallon. This will leave 4 gallons of water in the 5 gallon jug.

Doing the above just reduced your chances of getting dementia or Alzheimer's Disease. For more on this see the article: 7 Ways to Prevent Dementia, Alzheimer's Disease and Type 3 Diabetes. The next part of this is a trick based on science that I learned when I was young. I then went on to show it to every kid that I knew.

Apparently I have a problem spelling dementia the right way. I sometimes spell it as dimentia that is an incorrect spelling. One webpage has it spelled the wrong way in the title to get visitors spelling it wrong and then tell them the correct spelling.

Amazing Anti-Gravity Water Trick is what this is called on the video below.

You fill a glass with water. Put a playing card on the top of the glass. Hold the card on it while turning it upside down. Then take your hand off the card and the water and card stay there without falling to the ground. The science behind it is that the air pressure on the card is greater than the force of gravity so the card stays on the glass. I have also seen this done with the glass half filled with water.

See video below. I never knew until watching this video that you can take the card off in just the right way and the water will stay in the jar or glass. This is something that you can practice until you are able to do it. Then when you can do it and others cannot, you can play a trick on them and tell them you have psychokinetic power that is the ability to move things with your mind and that is how you can do the second part with removing the card.

Anti-Gravity Water Trick

Books with More Puzzles to Exercise Your Brain


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