Experiments 8-10: Playing with Gas Pressure

The next 3 experiments all deal with gas pressure. They are among my kids favorite experiments - but, as boys, anything exploding or seeming like magic will always be a hit!

Experiment 8: Exploding Soda

CAUTION: you'll want to do this outside away from your house, as it makes a fantastic mess.

Supplies:
2 liter bottle of soda unopened 1 package of mint mentos

Process:

1) set the soda bottle in a wide open space and carefully open the top. (don't shake up the soda as you want as much of hte carbon dioxide to remain in the bottle as possible)
2) this is the tricky party. You'll want to drop at least 5 mentos into the soda at the same time. I stacked the mentos carefully so they could drop, one right after the other into the bottle.
3) duck and run! The soda will shoot up about 15 feet into the air!

Explanation:

Soda is backed with carbon dioxide, that's what all the fizz is about. A mento may seem smooth on the surface, but in actuality the entire surface is pitted with hundreds of microscopic holes. When they are dropped into the soca much of the carbon zooms through these holes, building up the gas pressure to explosive levels, as the pressure inside the bottle becomes greater than the air pressure outside, the liquid seeks to go where there is less pressure, outside the bottle. This is a similar concept to releasing a blown up balloon - it will zoom around as the pressure within the balloon is rapidly released.

Experiment 9: the Coin Launcher

Supplies:

1 small bottle of soda, empty (16 oz is a good size)
1 pieces of tissue paper
1 quarters
Freezer
Safety glasses

Process:

1) put the top on tightly on the empty bottle, also place it in the freezer
2) let sit for About 30 minutes
3) observe what changes to the bottle, but leave it in the freezer so it doesn't warm
4) wrap the quarter in the tissue paper
5) get the paper wet
6) with the bottle still in the freezer, remove the top and place the tissue wrapped quarter over the opening.
7) allow to sit in freezer until tissue is frozen
8) take bottle out of the freezer. Wear the safety glasses!
9) gently warm the bottle in your hands pointing away from you. Watch what happens!

Explanation:

When the bottle is frozen it shrinks as the air molecules pull toward the middle of the boodle. When the frozen tissue is in place of the top, it should maintain this vacuum. (if he coin doesnt shoot off, then the tissue dint form a good enough seal). When the bottle is then warmed the air molecules push back away from the center. This causes a change in pressure that pushes the coin away.

Experiment 10: Magic Card Trick

We actually first did this trick last spring for a local science fair. My youngest did the next two experiments as a part of his display on the awesome capabilities of air & water pressure!

Supplies

Small glass or plastic cup (it must have a rather sharp or flat rim with no bends)
Water
1 index card

Process:

1) fill the glass about 3/4 of the way full of water
2) lay the index card flat across the open end of the glass.
3) support the card with the flat of your hand as you quickly turn the cup upside down
4) remove your hand, amaze your family & friends with the fact that the card stays in place and doesn't fall!! (don't leave it too long upside down though, once the water soaks into the card enough it will destroy the seal and the water will go everywhere!)

Explanation:

The reason the card stays in place is based on 2 laws. First Newtons second law of motion: "every action has an equal and opposite reaction" and air pressure vs water pressure. (or more specifically air pressure vs the force of gravity)

Essentially the water in the cup is pushing down with the force of gravity (9.8 meters/second squared). While this force is pointing toward the ground, the air outside the cup of pushing upwards on the card. For a period of time this creates a seal between the card and the edge of the cup. Furthermore there are way more air molecules outside of the cup than there are water molecules inside the cup. This is the true reason for the 'magic'. All air molecules are trying to raise up. This means there is a pressure imbalance. It's like having a car hit a brick wall. If it is a small wall the wall will be destroyed by the car - because there are too many molecules in the car acting against the fewer molecules in the wall. But if it is a gigantic stone wall (like a concrete bridge support) then the car is the one with more damage - as there are more molecules in the wall than there are in the car.

Experiment 5: Plastic Milk

Ok, I love chemistry! I think is is so fun, and educational, when you can see with your own two eyes some substance radically change. In this experiment you can change a glass of milk into a plastic! (no joke!)

Supplies:

• 1 glass of full cream milk (I also suggest doing this with a variety of creams and milks if you can afford it - whipping cream, whole milk, etc, to see how it affects the results)
•  vinegar
• eye dropper
• wooden/plastic spoon
• microwave (or a bowl of freshly boiled water)

Process:

1. fill a glass about 3/4 of the way with the whole cream milk
2. microwave the glass for about 1 minute until milk is warm
3. Fill the eye dropper with vinegar
4. stir milk with spoon as you slowly add the vinegar
5. Hold your hand over a sink (MAKE SURE THE MILK ISN'T TOO HOT!) pour the 'milk' over your hand, catching the plastic!

Explanation:
The cream in the milk contains a chemical called casein. When you add the vinegar, the casein separates from the rest of the milk. The molecules on casein are loosely bonded together in a chain, making form on plastic! Casein is a bonding protein found in many foods that contain Phosphoric Acid. It really is also included in may products like plastic, paint, etc. Therefore, it can be found in two forms: edible and technical. Casein is similar to salt in that it doesn't change form when added to a substance. I this experiment we can see that, as we are just separating those molecules from the rest of the molecules in the milk. Casein is a protein and acts as a binding agent. So it is an important part of making cheese and yogurt. On a side note: there have been studies that show a link in adverse effects of casein in those with autism. Many with autism have food sensitivities, similar to allergies. So families will avoid dairy, thinking they are avoiding the allergy, not realizing it is the casein (found in various other foods) that might be the culprit.

Experiment 4: Eddy Currents

As many of you know I used to be an aeronautic engineer. I helped design holographic inspections for the rockets for NASA and I also worked with Eddy Currents, used as a non-destructive testing tool. You see, there are often microscopic scratches on the surfaces of jet engine parts.the vibrational forces exerted on an engine in use, and over time, can cause these scratches to propagate into actual cracks. In order to prevent catastrophe, engine makers use ultrasound and eddy currents to detect these microscopic cracks, so they can be sanded away. Eddy currents are very cool. Anyone with a strong magnet can see them in action. So I thought I'd include an experiment that demonstrates this phenomena - which is great for kids of all ages!

What you'll need:

•   A strong magnet
• A section of copper pipe
• A section of some other material pipe (or even a toilet paper/paper towel roll)

Process:

1. Stand thepipes up on end, or your student can hold them in their hand, vertical.
2. hold the magnet over the opening on one end of the non-copper tubing
3. let the magnet drop, it will fall right down at the forces of gravity
4. now hold the magnet over the opening at one end of the copper tubing
5.  let the magnet go, watch what happens!

Understanding the experiment:
The magnet will float in the copper tube. This is the result of a specific form of Electro-Magnetic force called the Eddy current. As you know, copper is a conductor of electricity. When the magnetic field interacts with the surface of the tube, the metal begins to generate its own magnetic field/current. This was discovered by a scientist by the name of Michael Faraday. The magnetic field created in the metal opposes the one surrounding the magnet. What happens when the same polarized ends of 2 magnets interact? They push eachother away. The same is true here. The magnetic field generated in the pipe is calle the Eddy Current. This all falls within the Physics law called Lenz's Law. Older kids can research Michael Faraday and the Russian physicist Heinrich Lenz. For another simple experiment demonstrating Lenz's Law, check out the Swinging Magnet experiment http://www.ndt-ed.org/TeachingResources/NDT_Tips/LenzLaw.htm

Experiment 3: Acids & Bases

For today's experiment we will be doing some kitchen chemistry. It's super easy and fun for kids of all ages! Experiment - Determining pH

What You Need-

• Some Red Cabbage
• Lemon Juice,
• Baking Soda,
• Cola,
• Water,
• Vinegar
• Oil,
• milk of magnesia (if you have it on hand)
• PH chart (like the one found http://www.elmhurst.edu/~chm/vchembook/184ph.html )
• Medium sized bowl
• Grater
• Strainer
• Clear cups
• Some plastic containers

Process:

1. grate some cabbage into the medium sized bowl
2. Cover cabbage with cold water and allow it to sit for 45 minutes.
3. Strain the water mixture into a plastic container
4. Pour an equal amount of juice into the cups
5. Add 1 tsp to all but one of the cups. Mix. This should turn the mixture blue, as baking soda is a base.
6. Add lemon juice to one of the blue cups, a little at a time. How much do you need to add before bringing the color back to normal?
7. repeat #6 for each of your other liquids. One in each cup. If the liquid remains blue, then your substance is a base. But you should notice different liquids require different amounts to change the color back to normal.

  Reasoning:
We use red cabbage because the chemical makeup of the juice allows it to dramatically change color when mixed with other substances. This makes it easy to see the alkaline (pH) differences. Now, a little about pH - when you mix an acid and base, they cancel eachother out, neutralizing them. There are many neutral substances though, water and milk, for example. So, what is pH? Really all acidity is is a measurement of Hydrogen ions in a substance. They more hydrogen molecules in a substance the higher the acidity. Any substance added to water that causes an increase in the concentration of hudrogen molecules is considered an Acid. And substance added to water that decreases the concentration is considered a Base. The lase category of substances, as those that help resist changes in pH, these substances are called Buffers. As they help protect the water from changing pH level. Bonus: Now that you know which substances are acids. Think of which one would best remove the grime on an old penny. The substance with the highest acidity level. This is the one that you needed to add less of to turn the cabbage water back to its original color. Drop a penny in an old cup, add a bit of your acid ad watch it work!

Experiment 2: Inertia & Tensile Strength

I love inertia, it's so fun to play with! This experiment will greatly get these kids thinking. Have them brainstorm as a team to come up with a hypothesis (prediction) of what they think will happen and WHY. We have experiment journals, here the kids keep track of the supplies, process, hypothesis, and results from all our daily experiments. Most of our experiments use things you should have readily available around the house.

  SUPPLIES:

• Water bottle (or small soda bottle)
• 4 Pieces of string about 40 cm long (cotton is best, but you can judge the tensile strength of various fibers in another experiment)

PROCESS:

1. tie one end of 2 pieces of string around the neck of the bottle
2. tie the other end of ONE of the strings onto something solid like a railing, so the bottle will hang down
3. holding the other end of the other string in your hand. Pull slowly. Where will the string break?
4. repeat steps one-three, but this time jerk the string quickly. Where does it break now?

Understanding Inertia: Inertia is a part of Newtons First Law of Motion. "An object at rest wants to stay at rest, whereas an object in motion wants to remain in motion." Inertia is the measurement of how hard it is to get an object to change motion. For instance. One example of inertia would be how hard do you have to push the breaks to stop a car that is rolling downhill in neutral. Or, an example for kids, how much pressure do you have to apply to get your matchbox car to zoom across the room. In this instance. Inertia is proven because, in effect, the motion of your arm wants to continue on, but it comes to the length of the string. In order to maintain inertia, it breaks the string.....now, why do you think they broke in different places?

Understanding Tensile Strength: Tensile strength refers to The amount of stretching strength a material has before breaking. For instance, if you have a waterski rope, and try to tow a house with it, it will break because the force/weight of the object exceeds the tensile strength of the rope. But if you tow a boat with a thick chain, then it will probably be ok, because a steal chain has a high tensile strength. But if you add in inertia and momentum, then it decreases the tensile strength of an object because of Newtons Second law "Every action has an equal and opposite reaction"" so as you pull left an equal force yanks the rope left. The faster you pull the greater the force/momentum, the smaller the tensile strength...get it?

Experiment 1: Drinking Water from Salt Water

I don't know about where you are, but it's been hotter than Billy Blue Blazes here. (though, now I'm curious about who Billy Blue is and who set him on fire....lol). One of the ways we try to bear the heat is through doing experiments. They can be fun, cheap, easy and educational! Drinking water is becoming more and more scarce the world over as fresh water supplies are evaporated due to global warming and droughts. You can use the following resources to do some research on the current water shortage situation: http://drinkingwaterz.com/2369-shortage-of-drinking-water.html http://whyfiles.org/131fresh_water/2.html

One of the things that has intrigued scientists from the time we emerged from the caves, was how to take the plentiful salt water of the seas and oceans and make them palatable for drinking. Ok, onto the experiment, this is a small scale version of one of the methods scientists are evaluating.

  Supplies:

• 1-2 TBS table salt
• bowl
• 3 cups water (tap water is fine)
•  small bowl or coffee cup
• stone
• thick plastic wrap

Procedure:

1. pour watere into the larger bowl
2. mix salt into the water until it is dissolved
3.  place the small bowl or cup into the water CAREFULLY, you do not want to let any of the water to flow ov the sides of the cup.
4. Place the stone in the center of the plastic wrap, so at the wrap angles down into the cup a bit.
5. carefully place the bowl in the sun
6. wait several hours. You should see water droplets on the inside of the plastic wrap dripping into the cup.
7. after a few hours allow student to taste the water in the cup - it won't be salty!

What happened:
The water from The bowl evaporated, condensing on the underside of the plastic wrap (which is why heavy duty plastic wrap is so important, lesser quality plastic wrap will allow the water vapor to escape and leave the cup empty.) salt doesn't evaporate, so essentially the evaporation process separates the water molecules from the salt ones.