Imploding Can

Teacher Demonstration 19 Imploding Can

Materials: • Empty soft drink cans • Gas cooker (or Bunsen burner) • Cold water* • Glass jar or bowl • Tongs • Table spoon • Oven mitten (or glove)

* Note: if ice is readily available in your classroom, add some to your water for an even more spectacular result

Instructions

This very reliable and dramatic demonstration of atmospheric pressure will shock and amaze your students. A small amount of water boiled inside a soft drink can causes it to implode instantaneously when submerged into cold water. The loud crunch is echoed by a long “woooh!” followed closely by “do it again, do it again!”

1 Fill a bowl or jar almost to the brim with cold (if possible, refrigerated) water.

Note: tap water works fine but colder water yields more spectacular results – use refrigerated or icy water if possible

2 Optional: add several ice cubes to the water if available – the results is more spectacular with colder water.

3. Add four or five tablespoons of water to the empty soft drink can.

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3. Use tongs to hold the soft drink can over the flame of a gas burner until the water boils (you’ll hear the water bubbling). Keep boiling the water for approximately 15 seconds.

Note: hold the tongs with your wrist facing up as shown so you can invert the can in one smooth motion – you’ll need your spare hand to turn off the gas burner

4. Turn off the flame with your spare hand, bring the can above the bowl of water, then turn it upside down submerge the hole into the cold water.

Note: don’t turn the can over until it is over the bowl because the remaining water will spill – you will hear loud fizzing as the water inside the can runs down onto the hotter parts of the cane - you don’t need to submerge the whole can in the water

5. CRUNCH!!! The result is instantaneous!

Note: the can will more than likely be ‘pulled’ out of the tongs and into the water – a few drops of cold water may spray out of the bowl

6. Hold the can up so students can observe the dramatic result.

Note: the can will be cold enough to touch almost immediately

Safety notes

This demonstration is safe if the common sense precautions associated with the use of a portable gas stove are observed. Discuss the safety precautions you are taking with your students and insist that they only attempt to repeat this demonstration under the supervision of an adult.

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The imploding can demonstrates several scientific concepts which are summarised below.

1. Water is a liquid below1000C and a gas (steam, water vapour) above 1000C (ie the boiling point of water is 1000C (at sea level) air at room temperature

air inside - air outside pressure inside = pressure outside water (cold)

heat off

2. Water expands to approximately 600 times displaced air 0 its liquid volume when heated above 100 C escapes

3. The hot water vapour produced displaces almost all the air inside the soft drink can

water vapour inside ↔ air outside pressure inside = pressure outside water (boiling)

heat on

4. Hot water vapour condenses into liquid hot water vapour water when cooled condenses back to liquid causing a sudden drop in 5. The volume of the condensed water is internal pressure approximately 600 times less than the previous hot water vapour volume

hole in can is water vapour inside ↔ air outside blocked by water so no air can get in low pressure inside ↔ high outside

6. Atmospheric pressure outside is now much can is crushed by the greater and immediately squashes the can much larger external atmospheric pressure while simultaneously forcing water up into

it water simultaneously forced up into can water inside ↔ air outside pressure inside = pressure outside

Note: water has considerable inertia (ie mass), so it takes a fraction longer to be forced up into the can than it takes for the can to be deformed – a sufficiently strong container would not deform but would instead fill with water until the internal and external pressures are equal

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