Liquid Nitrogen
Age
Elementary School, Middle School, High School
Format
Stage Show
Materials
Liquid Nitrogen & Safety Equipment (Thermal Gloves and Safety goggles) 2 Thermos containers (for presenting) Tongs Balloon Ball and Hoop Bimetallic Strip 1 Racquetball Flowers 2 Bananas Nails Hammer Ladle 1 Small Bowl Soap Small Blast Shield 1 Hot Dog (optional) Rubber Gloves (optional) Red Food Dye (optional)
Safety Precautions
Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. LIQUID NITROGEN CANNOT BE TOUCHED WITH BARE HANDS! KEEP AWAY FROM ANY BARE SKIN!
A proper storage container is essential for transporting, transferring, and handling liquid nitrogen. These arrangements must be discussed with the supplier. Be sure not to store the liquid nitrogen in a container that can be sealed. The container may explode and can possibly inflict injury. Liquid nitrogen is stored in a Dewar, which will keep it cold for long periods of time. However, even in a Dewar, liquid nitrogen warms up and evaporates.
When working with liquid nitrogen, proper safety equipment MUST be used: safety goggles and thermal gloves must be worn at all times by all people working around the liquid nitrogen. It should be noted that most thermal gloves designed to work with liquid nitrogen will allow liquids to pass through them and saturate the material. Extreme caution should be exercised so that no liquid nitrogen contacts the gloves, as severe frostbite WILL occur.
Liquid Nitrogen is many times colder than most people have experience with and they do not comprehend how cold it is. Be sure to take special care with liquid nitrogen around younger students. Never keep it within touching distance and never leave a Dewar of liquid nitrogen unattended. It should be explained to audiences that a trained person using safety gloves and goggles must handle liquid nitrogen carefully. NEVER use liquid nitrogen in a demonstration without gloves and safety goggles.
Do not let students touch the ball or hoop after it has been taken out of the liquid nitrogen. Be extremely careful with the ball and hoop when using it in a glass (silvered or non-silvered) Dewar. You should NOT allow the hoop to come into contact with the Dewar sides or bottom. You may wish to consider performing this demonstration in a metal mixing bowl. This warning is advised for ANY metal object that needs to be placed in liquid nitrogen.
The racquetball, flowers, bananas, and hot dogs should be handled by Science Theater performers only, and with thermal gloves at all times. Audience members may want to touch the pieces after the experience, but there is still risk of freezing-related problems. Feel free to show some of the pieces, but wear gloves at all times and tell the audience members to not touch. In addition, objects will shatter when broken. Consider breaking the objects behind a clear shield. Always keep the audience members a safe distance away.
Preparation
Keep the liquid nitrogen in a safe container at all times. Set up the demonstration in an area that is safe in the room and approved by the teachers/faculty. Be sure to keep the audience a safe distance away, and performers must always wear the safety equipment. Have tongs ready for dipping objects. Perform the demos in any order you wish and as many as you’d like. The order this wiki is written in is:
Molecule Dance Balloon Frozen Soap Bubbles Banana Hammer Frozen Flowers Frozen Hot Dog Finger Leiden Frost Effect Ball and Hoop Bimetallic Strip Racquetball Ice Cream
Demonstration
1. Molecule Dance (Optional):
Ask for as many volunteers as you can possibly have standing, and have them stand off to a side where there is room to move. Let them know that they are about to do the MoLeCuLe DaNcE!!!! (Say it like it is the most exciting thing in the world.) Make sure that your fellow presenters join in the dancing. First, have your volunteers dance like room temperature molecule (not fast, not slow, and shuffling around the room). Then have them dance like hot molecule (fast, moving a lot, bouncing off one another). Transition back to room temperature, and then have them dance like cold molecules (slow, huddling for warmth). Thank the volunteers and have them take a seat. *note: if you have music to play, then use it! Play a fast song, a casual song, and a slow song for the different molecules.
2. For Balloon:
Take out a balloon and blow it up. With safety gloves or tongs, dip the balloon into the liquid nitrogen. The balloon will shrink considerably. If necessary, use the tongs to submerge the balloon into the container. Take the Balloon out of the Liquid Nitrogen. It will expand back to its original size quickly. You may need to blow on parts of the outside of the balloon if they are frozen, otherwise it will pop.
3. Frozen Soap Bubbles:
Take the small bowl and fill it with some soapy water. Using the ladle, scoop some of the liquid nitrogen and pour it into the bowl. It will bubble, and some of the bubbles will freeze. Alternatively, you can take the bowl of soapy water and dump it directly into one of the show thermoses. You must pour it fast, however, for the result is a small explosion of soap bubbles, leading to a good portion of them freezing within seconds of formation. You can then scoop out the bubbles with the ladle and show them to the audience.
4. For Banana Hammer:
Demonstrate to the audience that the bananas are ordinary by pushing a nail into one. Place one banana into the liquid nitrogen using tongs. The banana takes a long time to freeze (about 5 min.), so it is suggested that you pair this up with the flower demonstration, as it is about the same principle (freezing organic matter). Be careful not to over-freeze the banana. If the banana is too cold, it will break into pieces as it is taken from the liquid Nitrogen. Instead, test the banana after a few minutes. When you are convinced that the banana is frozen, pull it out using tongs and, wearing gloves, demonstrate to the audience that the nail no longer goes into the banana. rather, you can show they the banana is hard enough to hammer the nail in. proceed to pull out the hammer and bang the banana lightly a few times to show how stiff it is, and hit it with one good swing to shatter it.
5. For Flower:
Demonstrate to the audience that the flower is an ordinary one whose petals are quite flexible by tapping it against the small blast shield. Ask the audience to make a note of any noise they hear. Dip the heads of the flowers into the Liquid nitrogen. Remove the flower after the bubbling has stopped, about 3 or 4 seconds. Hit the flower against the small blast shield. The flower petals will shatter like glass.
6. Hot Dog Finger:
(Warning: this demonstration should only be done either with a more mature audience or at the Halloween show. This takes a bit of practice to get down, and is one of the more risky demonstrations. Only perform this after being trained thoroughly) Before the performance, take a hot dog and peel the outside skin of it off to make it more closely resemble the width of a finger. Take a rubber glove and slide the hotdog into one of the fingers of the glove (it is suggested you use the pointer finger). Take a second glove and put it on your hand, then take your hot dog finger glove and slide it on over your gloved hand. Make sure to wear a glove on your other hand as well, so as to not have the audience questioning your one hand wearing a glove. *note: if you want to make this more gruesome, you can add red food dye to the hot dog finger once it is in the glove. This will lead to "blood spatter" when you shatter it.
Wear this glove throughout the beginning of the performance, up until after the banana demonstration. You will want to practice wearing this before an actual performance, so you can ensure your fake finger looks realistic while you are wearing it. Now is where it gets tricky. Ask the audience if they want you to show what happens when your hand goes in (they will, small children are terrible, terrible people). Take your fake finger and dip it into the liquid nitrogen. Keep it in there until sufficiently frozen, which will take between 30-60 seconds. You will be able to tell when it is frozen when you can feel the hot dog freezing to your hand. Be warned: the hot dog might make some pretty nasty cracking noises as it freezes, so be prepared for some ill-looking audience members. Take the finger out and, grabbing the hammer with your other hand, place it on your wood block and smash the hot dog. BE SURE TO SHOW THE AUDIENCE THAT IT WAS A FAKE FINGER AFTERWARDS. Explain the similarities between the finger and the banana performed earlier.
7. Leiden Frost Effect:
Only perform this demonstration if you have been trained on what the effect is and how to hold your hands. Ask the audience for reasons why you are not wearing the thermal gloves all the time. Proceed to asking if you should try dunking your hand to see if it will freeze (they will want you to. children are awful). Take your hand and position it above the container of liquid nitrogen. Dip your hand straight in, and pull it straight out immediately. Your hand will not have frozen in any way. Take a ladle with one hand and scoop some of the liquid nitrogen into it. Holding your hand at a 45-degree angle to the horizon aiming downward, pour the liquid nitrogen on your hand. It will roll off and onto the floor. *note: some may catch on any hairs on your hand and freeze water on your hairs. This might tug slightly, but should not give you freezer burn. In addition, after you have been trained and are sufficiently comfortable with this demonstration, you can add a little flair when you dunk your hand, such as scooping slightly as you pull it out to make a splash. Do NOT, however, attempt this if you are not comfortable with this demonstration.
8. For Ball & Hoop:
Show the students that the ball fits easily through the hoop. Place the hoop into the liquid nitrogen and let it cool. The cooling will take about 2 minutes. The liquid nitrogen will bubble when it meets the hoop. This bubbling will continue until the hoop becomes close to the temperature of the liquid nitrogen. It is suggested that the students discuss possible outcomes during this time or that another experiment is started to keep the audience interested. When the hoop is cooled, try to put the ball through the hoop. The audience will notice that the ball no longer fits. As the hoop warms up, the ball will start to slide through. *note: in order to make this effect more prominent, you may want to bring a blowtorch with you and heat up the ball while the ring is cooling down. That way, you have the ball expanding and the ring contracting, thus leading to a more convincing display of this effect.
9. For Bimetallic Strip:
Present the bimetallic strip to the audience and explain that is a strip that has a different metal on each side (Bronze on one side, Nickel on another). Dip the strip into the liquid nitrogen for a few seconds. It is not necessary to cool the strip completely. When the strip is pulled out, the audience will notice that the strip bends to one side.
10. For Racquetball:
Convince the audience that the racquetball is flexible by bouncing it a few times on the floor. Using tongs, place the ball in the liquid nitrogen and wait until the bubbling stops. The racquetball takes a long time to cool down (about 5 minutes), so we suggest that you talk with the audience about what is happening to the ball or perform another demo while waiting. Remove the ball and try to bounce it away from the audience or into a shield. The racquetball will break if it is thrown onto a hard enough surface. If you are in a gym, you may need to throw it against a concrete wall (away from the audience).
11. For Ice Cream: The recipe for LN₂ ice cream is: 1 cup of sugar 1 quart of half and half 1 quart of heavy whipping cream 1 tablespoon vanilla flavoring other flavoring agents (sprinkles, chocolate syrup, fruit bits) to taste. Mix the sugar, half & half, heavy whipping cream and vanilla in a large mixing bowl. Slowly add the liquid nitrogen as you stir, and continue to add it until the ice cream reaches the desired consistency. For the 2 quarts of ice cream that this makes, you will use about 2 quarts of liquid nitrogen. Serve fresh and allow your customers to add toppings as they wish.
What to Say: Ask the audience what they know about temperature, besides just weather. If no one answers, ask for the differences between a solid, liquid, and gas 9and plasma, if someone mentions it). You will likely get the three different states of water: Ice, liquid and steam. Then ask for volunteers and perform the Molecule Dance.
After the dance, explain that the molecules of each have a different kinetic energy, which is determined by how hot, or cold they are. The hotter they are, the faster the molecules move, and vice versa. Then it's time to get excited about Liquid Nitrogen. Stress how cold it is. "So as you can see, it's not just cool. It's cold!" 'bad pun #1' (77 degrees Kelvin, -326 degrees Fahrenheit) and make sure to warn the audience members not to try this experiment at home. A good safety pun would be: "So have any of you seen A Christmas Story? -Most will have- All right. So do you remember the scene where Ralphie's friend sticks his tongue to the pull and gets stuck? -Some chuckles, nodding of heads- Well; Liquid nitrogen will do that to you, except you'll be stuck to whatever you are touching at the time. This is why we cannot let anyone in the audience get too close to the liquid nitrogen, because we'd rather not get you stuck to the floor or something -bad pun #2-"
Start the Balloon demo. Inflate the balloon and show how the pressure increased from a greater amount of gas molecules pushing against the walls of the balloon. Ask the audience "what do you think will happen when I put the balloon in the Liquid Nitrogen?" Place the balloon in the liquid nitrogen, watch it deflate, and ask the audience if they know what caused the change. The kinetic energy of the molecules decreased from the extreme drop in temperature. The molecules slowed down, and decreased the amount of pressure inside the balloon. "To 'expand' on this idea 'bad pun #3' We will now look at bubbles!"
-Pull out the Frozen Soap Bubbles demo- "So here I have some soapy water. What do you think will happen when I put the liquid nitrogen in? -get responses- well, let's find out!" -Pour some in, watch the reaction- "So what just happened here you guys? -Responses- So you can see that the water started bubbling. Is it really hot, or is it because of something else? . . Well, keep in mind how cold the liquid nitrogen is. It's currently boiling, and turning back into a gas, so some of that gas was caught in the bubbles. However, because it is so cold it froze the bubbles! Now this is cool and all... cool? Get it? 'Bad pun #4' but we can show this in a better way. Can I get a countdown? 3! 2! 1!" -Dump the soapy water in the container, watch it explode with bubbles- "Whoa! Now THAT was awesome!"
Now switch to the Banana Demo. Ask the audience on what a banana is mostly made of. Encourage the answer of "water". Explain that the water in the banana might freeze while it is in the Liquid Nitrogen. While the Banana is freezing, you can start the Frozen Flower demo. Pull out the flower. Show that it’s normal and even ask an audience member to look at it and feel the petals and say if it’s like a normal flower. Once they agree, place the flower into the liquid nitrogen, pull it out, and bang it against a hard surface. "Poor flower petals, they didn’t stand a chance…" Ask the audience what they believe happened. Hopefully someone will say that the flower froze, which is absolutely correct! Explain that the water in the flower froze, making it more brittle. However, water expands when it freezes (unlike most other materials) which lead to the cells in the flower bursting, and the sound of shattering glass when we broke it. Take out the banana, and explain that the banana, like the flower, is now frozen. If you can, hammer the nail into the board. Then, while grabbing the hammer and pounding the banana lightly, explain that "The banana -bang- has frozen solid -bang- and clearly -bang- is no longer soft -bang- which is why -bang- we can pound it -bang- without it going to mush -whack it hard to shatter it- but we can shatter it."
If it is being performed, you would now go to the Frozen Finger demo.
Now, what would happen if we placed a part of the human body into the liquid nitrogen? Do we have any volunteers?!? … That’s alright; we won’t actually put one of you into the liquid nitrogen. Instead, who wants to see me put my finger in here? (Most will say yes, and at this time you get concerned for your well being) . . .Re-really? I was only kidding. . .I mean, do you realllly want to see me stick my finger in? (YES) oh. . okay then. . . (proceed to stick the finger in slowly, and make sure to flinch and be acting like it is the worst pain ever while explaining) "So my finger (ow!) is right now (sharp intake of breath) being frozen by the (aaaahh!) liquid N(Ow!) nitrogen (ow ow ow!) which means that the water (AAhh!) is bursting the cells (OW!) in my finger (whimpering pain, feel free to take a moment here) which means my finger (slowly pull it out) is no longer useful. . . well (pull out the hammer) let's get this over with. . . Proceed to put the finger on the wood block and, before the audience had time to react, smash it. Flinch, pull your hand away, do whatever you want to make it seem like you really did just smash your finger off. Then, stop faking and take the glove off, showing your real finger to be intact "So as you can see now, I was kidding and my finger is still here. But what about the fake finger? -Get responses- So you can see that it did freeze, and it is true that by sticking my hand it like that that my hand would freeze off like that.
As you have all noticed, we encourage safety throughout this show at all times, so that we don't risk freezing any of you and keep you safe. . . So, if that is the case, then why aren't I wearing my safety gloves all the time?" -Lead into Leiden Frost effect-. "So you may be wondering if it is actually unsafe for me to not be wearing my safety gloves all the time. Well, there's only one way to find out. Who wants to see me stick my hand in the liquid nitrogen?" -YEAH! - (feel free to make a comment about how evil everyone is, they'll chuckle at it) "Ok then, here it goes. So 3, 2, 1, -stick hand in and out quickly- huh. . .I'm not frozen. . . should we try again?" -YEAH!!- "Ok then. 3, 2, 1, -repeat- . . . I'm still not frozen . . . let's try pouring it on my hand! -Pull out the ladle- "Now there is something I Have to tell you guys. The reason why it is not freezing my hand is due to the Leiden Frost effect -have them repeat it a few times- This effect has to do with temperature. Because I am at 98.6 and it is at -326, there is a big temperature difference of over 400 degrees! This means that, when it lands on my hand, some of it turns right into a gas, and the rest of the liquid -pour it across your hand- rolls on the gas and off my hand! In fact, you can also see it roll across the floor!" -Make sure none of them touch it as it rolls on the floor-
Next switch to the ball and hoop. Show the audience that the ball fits easily through the hoop. Then ask, since the balloon deflated when placed into liquid nitrogen, what do you think will happen if we place this hoop into it as well? Let the audience answer the questions while the hoop cools in the liquid nitrogen. When it’s finished, try to move the ball through the hoop, only to discover it doesn’t fit! If you wait a little while, the ball will fit through again after it warms up. Describe how the kinetic energy of the molecules decreased again. When the kinetic energy of molecules is lower, they are more likely to take up less space than when warmed up.
Expand on the idea of thermal expansion and contraction by introducing the bimetallic strip. Point out that the strip is made up of two separate metals. Ask the audience for any predictions as to what may happen after the strip is placed into liquid nitrogen. When the strip has reached the correct temperature, pull it out part way, and present the magic of the strip bending to one side! Remind the students that the strip was composed of two different metals. The metals contracted at two different rates. The one that had a larger coefficient, according to linear expansion, contracted more and made that end of the strip bend more.
For a finale, use the racquetball demo. Start off by showing the audience the racquetball and bouncing it, stating the obvious things such as "see how it is bouncy". Then, close it inside the tongs and place it within the liquid nitrogen. While it is cooling, you can explain what is going on. "So, as you all know by now, the liquid nitrogen is extremely cold. So what is happening to the racquetball?" -Chances are you will get a few people who will say that it is freezing- "well, keep in mind that a racquetball is made of rubber, which cannot freeze. Also, it is not a metal, so although it will contract, it won't contract enough to show a difference. So what do you think will happen to the ball then when I pull it out? -get a mix of answers, edge people towards saying that it will not bounce- "So have any of you ever put a rubber band in a freezer? -Some yes- and what happened to the rubber band? It didn't stretch as well, right? Well, there is a reason for that. Rubber and other elastic materials are affected strongly by temperature. If you were to take a bouncy ball and play with it on the hottest day of the year, it will bounce higher than if you were to try bouncing it in the middle of winter." At this point, the ball should be ready, so pull it out and gently drop it on the table. It will go -thud- and barely bounce back. "So as you can see, the ball is no longer going to bounce. Instead" -chuck it all the wall/floor, and it shatters- "the ball has lost so much elasticity, that it can no longer handle hitting the floor/wall! It shattered!" -gather up the pieces of ball, and place them on the table. Kids can look at them once they warm back up- "So as you can see, the ball shattered when I threw it. What made it so the ball could no longer bounce? (Liquid nitrogen, extreme cold) Exactly. This poor ball hit the floor like your grandmother's fine china. . . Which I STRONGLY suggest never dropping. EVER." "So what what on earth was that loud sound when the ball hit the ground? Well that was related to the pressure inside the ball. See, a racquetball is hollow and has a certain pressure inside of it at any given temperature. When it gets colder, the pressure decreases as well, because the molecules aren’t hitting the sides as quickly anymore, like with the balloon. So when the ball broke, what you heard was all of that compressed air decompressing. The ball could not deflate like the balloon did earlier because it is not flexible enough to do so."
Close the show, and at this point, you would have someone else start with closing remarks as you prepare the Liquid Nitrogen Ice Cream.
Substance:
Gold 14
Aluminum 23
Glass (common) 8.5
Brass 19
Iron or Steel 12
Concrete 12
Silver 19
Copper 17
Lead 29
Why It Is
The audience should be made aware that molecules compose all solids, liquids, and gases and that they are in constant motion. It is important that they understand that the motion of these molecules depends on the temperature of the substance. The point of this demonstration is to show how the molecules move faster when the temperature is higher and move slower when the temperature is lower. This relationship between the motion of molecules and temperature is called kinetic theory. The important thing to understand in these equations is that kinetic theory relates the temperature of a material to the average velocity of an individual particle. In other words, as the temperature of a gas is increased, then the velocity of the molecules composing that gas will increase as well. This model of temperature as it relates to the movement of molecules is a very powerful one and can be used to explain many different temperature-related phenomena. The first one is that temperature will affect the expansion and contraction of objects. This is the core concept at work in the first set of demonstrations. When a gas is cooled down the molecules will move slower and stay closer to similar molecules due to slight attractions. When a gas is heated up, the opposite occurs and the molecules will begin to move faster and overcome any attractions or interactions, moving further away from each other.
Real Life Examples
This is analogous to people in the winter, people stay inside their houses and huddle together because it is so cold. However, in the summer, people go outside and move around because it is warmer. Of course, molecules are not like people in that they do not make decisions to go out or stay in. The movement of molecules is completely dependent on their temperature. A real life example of linear expansion of different materials occurs when a glass jar has a stuck metal lid. When presented with this situation many people will try to put the jar under hot water. The hot water causes the molecules in the metal lid to move faster, causing it to expand. The jar is easier to open now because the lid is not as tight around the jar. The glass jar also expands, but not as much as the metal lid. That means that glass will expand less than any metal when heated to the same temperature.