Growing Bacteria For Science Fairs

petri-dish


Testing for bacteria (germs) can be a great idea for a science fair experiment since there are so many possibilities for science questions, and because because carrying out the experiment is pretty easy using bacteria growing kits, (and yes, we have them at the Science Bob Store.) Besides, who doesn’t like checking out bacteria and fungus?

All good science experiments start with a question – this is what you want to find out by experimenting. Here are a few example questions to get you started using the scientific method for growing bacteria:

  • Is a dogs mouth cleaner than a humans mouth?
  • Who has the cleanest mouth in the class?
  • Do antibacterial soaps really kill bacteria?
  • Which door handle in the school has the most bacteria?
  • Does toothpaste kill bacteria in your mouth?
  • Do dark socks create more bacteria in a shoe than white socks.
  • Do hand sanitizers work to kill bacteria?
  • What location in the school contains the most bacteria?
  • Is there more bacteria in tap water, bottled spring water, rain water, or pond water?

Step 1 – Ask A Question: Let’s imaging that you want to answer the question, “Which door handle in the school has the most germs?”

Step 2 – Research: You can’t just jump in and start experimenting. It’s important to do a little research. Ask the school nurse which door handle he or she thinks the most germs (bacteria) are. Observe and chart which door handles get the most use, survey friends and family to get opinions and write down the results. All this information will help you narrow down which door handles are the most likely to contain germs – and which ones you should choose to use in your experiment.

Step 3 – Make a Hypothesis: This is when you make a prediction based on your research. This is not an “I think…” prediction, it is a statement that will either be proven true or false based on experimenting. An example would be, “The handle to the nurse’s room contains the most bacteria.”

Step 4 – Experiment: This particular science experiment requires a simple bacteria testing kit. You would choose several door handles that you think might contain the most bacteria. These door handles are considered the Independent Variable in your experiment because each handle is independent and you control which ones are chosen. In a typical kit you would touch a separate cotton swab to each door handle, and then touch it to the bacteria growing Petri dish so that you would have one dish for each handle. Take good notes that would include when you collected each sample and where you collected the sample, and be sure to label everything well in any experiment.

Step 5- Collect Data: In this experiment, bacteria will start to grow in the Petri dish over the next few days, and you may be surprised by just how much gross bacteria is lurking in your school. Take good notes each day and determine which dish has the most bacteria growing in it.

Step 6 – Make Your Conclusion: This is when you decide if your hypothesis is correct. If your hypothesis was, “The handle to the nurse’s room contains the most bacteria,” your experiment will show if your hypothesis was right. It is not bad at all if your hypothesis is incorrect, what is important is that you answered your question from step 1. Now pat yourself on the back for your fine scientific discovery using the Scientific Method.

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Bend a Bone with Vinegar

You will need

A jar large enough to fit a chicken bone
A chicken bone – a leg or “drumstick” bone works best
Vinegar

What to do

1. Have a nice chicken dinner and save a bone. Leg bones work best.

2. Rinse off the bone in running water to remove any meat from the bone.
3. Notice how hard the bone is – gently try bending it. Like our bones, chicken bones have a mineral called calcium in them to make them hard.

4.Put the bone into the jar and cover the bone with vinegar. It might be a good idea to put the lid on the jar or cover it – let it sit for 3 days

5. After 3 days remove the bone. It should feel different. Now can rinse it off and try bending it again. Is it really a rubber bone?

How does it work?

So what happened? What is so special about vinegar that it can make a hard bone squishy? Vinegar is considered a mild acid, but it is strong enough to dissolve away the calcium in the bone. Once the calcium is dissolved, there is nothing to keep the bone hard – all that is left is the soft bone tissue. Now you know why your mom is always trying to get you to drink milk – the calcium in milk goes to our bones to make our bones stronger. With some effort and you can really get the bone to bend.

MAKE IT AN EXPERIMENT

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Does the length of time the bone is in vinegar affect how much the bone bends?

2. Do smaller size bones become “bendy” sooner?

3. Do different types of vinegar affect how bendy bones become ?

Science Bob

Make a Cartesian Diver

Download the PDF

You will need

A clear ONE liter plastic soda bottle and cap (not the big 2 liter bottle)
A ball point pen cap that does not have holes in it
Some modeling clay (“sculpey” works too)

What to do

1. Remove any labels from your bottle so that you can watch the action.
2. Fill the bottle to the very top with water.
3. Place a small pea-size piece of modeling clay at the end of the point on the pen cap. (see drawing)

4. Slowly place the pen cap into the bottle, modeling clay end first. (some water will spill out – that’s okay) It should just barely float. If it sinks take some clay away. If it floats too much add more clay.
5. Now screw on the bottle cap nice and tight.
6. Now for the fun part. You can make the pen cap rise and fall at your command. Squeeze the bottle hard – the pen cap sinks…stop squeezing and the pen cap rises. With a little practice, you can even get it to stop right in the middle.

How does it work?

Impressive, but how does it work? This eaxperiment is all about DENSITY. When you squeeze the bottle, the air bubble in the pen cap compresses (gets smaller) and that makes it more dense than the water around it. When this happens, the pen sinks. When you stop squeezing, the bubble gets bigger again, the water is forced out of the cap, and the pen cap rises.

If it doesn’t work: play around with the amount of clay and be sure the bottle is filled to the very top before putting on the cap.

Soy Sauce Diver: That’s right, next time you go to your local Chinese Food restaurant, ask for a packet of soy sauce (the kind they use for take out orders) Don’t open it – just put it in the bottle the same way instead of the pen cap. When you squeeze the bottle the air bubble inside the packet compresses and become more dense. The bubble in the packet makes it rise and fall just like the pen cap. This sometimes works with ketchup and mustard packs too. Have fun!

MAKE IT AN EXPERIMENT

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Does the size of the bottle affect how hard you have to squeeze the make the diver sink?
2. Does it matter if the bottle is not filled all the way with water?
3. Does the temperature of the water affect the density of the the diver?

Make a Simple Duck Call

You will need

One plastic straw from your kitchen or local fast food restaurant
Scissors
Lungs (don’t worry you already have them)

What to do

1. Use your fingers to press on one end of the straw to flatten it – the flatter the better.

2. Cut the flattened end of the straw into a point (see below).

3. Flatten it out again real good.

4. Now take a deep breath, put the pointed end of the straw in your mouth and blow hard into the straw. If all goes well you should hear a somewhat silly sound coming from the straw. The smaller you are, the harder it may be to get a good sound – sometimes adults can get more of a sound thanks to their bigger lungs. If you still have trouble, try flattening it out some more or cutting the straw in half.

5. Don’t stop there – try cutting the straw different sizes to see how the sound changes, or make another identical straw and add the pointed end of the new straw to the uncut end of the first straw (to make the first straw longer) The sound will be very different, (more like a moose call!) and you will have to blow even harder, but give it a try.

How does it work?

This is science? It sure is. You see all sounds come from vibrations. That little triangle that you cut in the straw forced the two pieces of the point to VIBRATE very fast against each other when you blew through the straw. Those vibrations from your breath going through the straw created that strange duck-like sound that you heard. Now you will never be bored again when you go to a fast food restaurant! Have fun!

MAKE IT AN EXPERIMENT

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Which size straw call sound the most like a duck?

2. Which length of straw is the easiest to get a sound? Which is the hardest?

3. Does the diameter of the straw affect the sound it produces?

BUILD YOUR OWN PERSONAL FOG TORNADO!

You will need

A copier paper box
A small 12 volt computer fan from a computer or electronics store. It should be at least 3×3 inches (8cm X 8cm).
A piece of clear plastic 10 X 17 inches (25cm X43cm) If your really in a hurry, you can test your fog tornado with clear plastic food wrap.
A small plastic food container
Dry ice (or other source of fog – see below)
Black paint
9-volt battery (if your fan doesn’t plug in)
Optional (but cool) battery-powered tap light
Adult help

What to do

Parts of the cardboard will need to be cut out using an exact-o blade.This part is definitely for an adult – kids hurt themselves every year trying to cut foam core and cardboard – don’t let that be you – know when to ask for help.

Follow the diagrams below, cutting away the areas marked in gray. IMPORTANT: Pay special attention to the placement of the slots. In order for the tornado to work, the slots will need to be in the correct place.

fog_tornado3


The opening at the top should be just a bit smaller than your fan.
The opening at the bottom should be bigger than the plastic food container.

Paint the inside of the box with flat black poster paint and allow it to dry.
Tape (or hot glue) the clear piece of plastic into the large window on the front. Be sure to keep the nearby slot open so air can flow through it.
Attach the tap-light to the inside of the top of the tornado box near the fan opening.
That’s it! Your Tornado Chamber is ready.

A note about the fog. I have found 3 decent sources of fog:

DRY ICE – Dry ice makes the best looking tornado, in my opinion, which is why I give the directions for it here. Dry ice should only be handled by adults. It can cause instant frostbite. Never handle dry ice without thick gloves and always wear safety goggles. Only someone familiar with dry ice and its dangers should handle it.
HUMIDIFIER – Many small humidifiers create a continuous source of mist that works well for the tornado chamber. You will need to find a way to mount the tornado chamber above your humidifier.
FOUNTAIN MISTERS – A fountain mister uses ultrasonic vibrations to create a light mist. They can often be found in stores that sell small fountains and in some pet shops.

FOG TORNADO TIME!

Turn on the battery powered light if you have one, and power up the fan. (red wire goes on the skinnier lead of the 9 volt battery) and place it on the top of the chamber with the breeze blowing up.
Place some small chunks of dry ice into your food container and add some warm water to create fog.
Put your tornado chamber over the container and watch the wonders of vortex currents at work!

How does it work?

As the fan forces air out of the chamber, air from outside the box is forced in through the slots on the sides. The position of the slots causes the incoming air to create a VORTEX (spiral) of air as it is drawn up and out of the box. Real tornados form in a similar way using updrafts and wind-shear (wind from different directions at different altitudes)

Make it an experiment

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Can you control the shape of the tornado by covering up parts of the slots?

2. Does a faster or more powerful fan change the shape of the vortex?

3. Do bigger boxes make bigger tornados?

BUILD A TABLETOP HOVERCRAFT!

You will need

An old CD or DVD disc
A 9” balloon
A pop-top cap from a liquid soap bottle or a water bottle
A hot glue gu

What to do

If you are using the cap from a water bottle, cover the center hole of the CD with a piece of tape and poke about 6 holes in the tape with a push-pin or small nail. This will slow down the flow of air and allow your hovercraft to hover longer.
Use the hot glue gun to glue the cap to the center of the CD or DVD disc. Create a good seal to keep air from escaping.
Blow up the balloon all the way and pinch the neck of it. (Don’t tie it.)
Make sure the pop-top is closed and fit the neck of the balloon over the pop-up portion of the cap. (This is usually easier with 2 people)
That’s it! When your ready to commence hovering, simply put the craft on a smooth surface and pop the top open.

HAPPY HOVERING!

How does it work?

The air flow created by the balloon causes a cushion of moving air between the disc and the surface. This lifts the CD and reduces the friction which allows the disc to hover freely. Large scale hovercraft are capable of traveling over land, snow and water.

Make it an experiment

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Does the size of the balloon affect the CDs ability to hover?

2. Does a helium balloon work better than an air filled balloon?

3. Do larger discs make better hovercrafts (plastic picnic plates, old record albums) ?

Rapid Color Changing Chemistry!

YOU WILL NEED

Sometimes it’s hard to tell SCIENCE from MAGIC – and this little demonstration is a great example of that. In this experiment you will watch an almost clear liquid suddenly turn dark blue in a flash. It takes a bit of preparation, and probably a trip to the pharmacy for materials, but we think it’s worth it.

IMPORTANT SAFETY INFORMATION: This experiment should only be done with the help of an adult. Iodine will stain just about anything it touches and it can be hazardous. Hydrogen peroxide can cause eye and skin irritation – safety goggles are needed throughout the experiment. Be sure your helpful adult reads the caution labels on each container.

3 clear plastic cups 4 ounces or larger
A 1000 mg Vitamin C tablet from the pharmacy (you can also use two 500mg)
Tincture of iodine (2%) also from the pharmacy
Hydrogen peroxide (3%) yep, also from the pharmacy
Liquid laundry starch (see below for alternatives)
Safety goggles
Measuring spoons
Measuring cup
An adult helper

What to do

Put on those safety goggles and mash the 1000 mg Vitamin C tablet by placing it into a plastic bag and crushing it with a rolling pin or the back of a large spoon. Get it into as much of a fine powder as possible. Then put all the powder in the first cup and add 2 ounces (60 ml) of warm water. Stir for at least 30 seconds. (The water may be a little cloudy) Let’s call this “LIQUID A”
Now put 1 teaspoon (5 ml) of your LIQUID A into a new cup and add to it: 2 oz (60 ml) of warm water and 1 teaspoon (5 ml) of the iodine. Notice the brown iodine turned clear! Let’s call this “LIQUID B.” By the way, you’re done with LIQUID A – you can put it aside.
In the last cup, mix 2 oz of warm water, 1 Tablespoon (15 ml) of the hydrogen peroxide and 1/2 teaspoon (2.5 ml) of the liquid starch. This is, you guessed it, “LIQUID C”
Okay, that was a lot of preparation, on to the fun part. Gather the friends and family and pour all of LIQUID B into LIQUID C. Then pour them back and fourth between the 2 cups a few times. Place the cup down and observe….be patient….somewhere between a few seconds and a few minutes, the liquid will suddenly turn dark blue!

How does it work?

This is an example of the chemical reaction know as the IODINECLOCK REACTION. It is called a clock reaction because you can change the amount if time it takes for the liquids to turn blue. (see experiments below) The chemistry of the demonstration gets a bit complicated, but basically it is a battle of chemistry between the starch which is trying to turn the iodine blue, and the Vitamin C which is keeping it from turning blue. Eventually the Vitamin C loses and, bam! – you get instant blueness.

Note: If you do not have liquid starch, you can also use 1/2 teaspoon of corn starch or potato starch. The liquids will be more cloudy and the reaction will happen a bit more slowly, but it’s still impressive.

Clean up: Carefully pour all liquids down the drain with plenty of water and wash your hands. Recycle the cups or dispose of them in the trash.

MAKE IT AN EXPERIMENT

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Does the temperature of the water affect how quickly the liquids turn blue?
2. Does the amount of Vitamin C added (Liquid A) affect how fast the liquid turns blue?
3. Does stirring the liquids more affect how fast the liquids turn blue?

The Magic Ketchup Experiment!

Amaze you friends and family when you make a pack of ketchup float and sink at your command while it’s sealed inside a bottle! It looks like magic, but it’s totally science.

You will need

  • A 1 liter plastic bottle or a water bottle
  • Ketchup pack from a fast food restaurant
  • Salt (using Kosher salt helps keep the water from becoming foggy)

What to do

  1. Remove any labels from the bottle and fill it all the way to the top with water.
  2. Add a ketchup pack to the bottle.
  3. If the ketchup floats, you’re all set – go to step 4. If the ketchup sinks in the bottle, go to step 5.
  4. For the floating ketchup pack simply screw the cap on the bottle and squeeze the sides of the bottle hard. If the ketchup sinks when you squeeze it, and floats when you release it, congratulations, you’re ready to show it off. If it does not sink when you squeeze it, try a different kind of ketchup pack or try a mustard or soy sauce pack.
  5. If the ketchup pack sinks, add about 3 tablespoons (45 ml) of salt to the bottle. Cap it and shake it up until the salt dissolves. (Kosher salt will keep the water from getting too cloudy, although it will usually clear up over time if using regular table salt.)
    Continue adding salt, a few tablespoons at a time until the ketchup is just barely floating to the top of the bottle.
    Once it is consistently floating, make sure the bottle is filled to the top with water, and then cap it tightly.
  6. Now squeeze the bottle. The magic ketchup should sink when you squeeze the bottle and float up when you release it. With some practice you can get it to stop in the middle of the bottle.

How does it work?

This experiment is all about buoyancy and density. Buoyancy describes whether objects float or sink. This usually describes how things float in liquids, but it can also describe how things float or sink in and various gasses.

Density deals with the amount of mass an object has. Adding salt to the water adjusted the water’s density to get the ketchup to float. Sound complicated? It is, but here’s the basics on the ketchup demo…there is a little bubble inside of the ketchup packet. As we know bubbles float, and the bubble in the ketchup sometimes keeps the heavy packet from sinking. When you squeeze the bottle hard enough, you put pressure on the packet. That causes the bubble to get smaller and the entire packet to become MORE DENSE than the water around it and the packet sinks. When you release the pressure, the bubble expands, making the packet less dense (and more buoyant) and, alas, it floats back up. This demonstration is sometimes known as a CARTESIAN DIVER.

MAKE IT AN EXPERIMENT
The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

  1. Do different food packs (ketchup, mustard, soy sauce) have the same density?
  2. Does the temperature of the water affect the density of the ketchup packet?
  3. Does the size of the bottle affect how much you have to squeeze to get the packet to sink?

Science Bob

The Lincoln High Dive!

You will need

A Lincoln penny (or other small coin)
A piece of card stock or stiff paper
A film canister, baby food jar, or other similar size container with an mouth slightly larger than a penny
Pencil or pen
Scissors

What to do

Cut the cardstock paper into a long strip about .75 inches (2 cm) wide and form it into a hoop as shown. The paper should be stiff enough to hold the hoop shape on its own and the hoop works best when it is between 3-4 inches (8-10 cm) across.
For dramatic effect, fill the film canister with water and place on a level surface.
Place the hoop on the film canister as shown and balance the penny on the top of the hoop.
Time for Lincoln’s big moment! Place a pencil through the center of the hoop and in one swift motion fling the hoop off to the side as pictured. If you do this correctly, the hoop will fly out of the way, and the penny will fall straight down into the canister with a splash. 10 points for Lincoln!

THE SETUP

THE DIVE

How does it work?

This is science? You betcha. Part of Newton’s first laws says, in general, that an object at rest will remain at rest unless acted upon by an outside force. The energy of your movement with the pencil was passed on to the hoop, making it fly out of the way quickly, but the hoop moved too fast, and there was not enough friction to affect the penny (at rest) on top of the hoop. The penny ended up above the film canister with nothing to hold it up. It was about then that gravity took over, and pulled the coin straight down into the waiting water. Yep, Issac Newton and Abraham Lincoln, together in the name of science…sort of.

MAKE IT AN EXPERIMENT

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

1. Does the size of the hoop affect the accuracy of the falling coin?
2. Does the shape of the object on the hoop affect the accuracy of the drop?
3. Is the coin affected by how fast you fling the hoop out of the way.

Science Bob

The Incredible Hoop Glider!

You will need

  • A regular plastic drinking straw
  • 3 X 5 inch index card or stiff paper
  • Tape
  • Scissors

What to do

  1. Cut the index card or stiff paper into 3 separate pieces that measure 1 inch (2.5 cm) by 5 inches (13 cm.)
  2. Take 2 of the pieces of paper and tape them together into a hoop as shown. Be sure to overlap the pieces about half an inch (1 cm) so that they keep a nice round shape once taped.
  3. Use the last strip of paper to make a smaller hoop, overlapping the edges a bit like before.
  4. Tape the paper loops to the ends of the straw as shown below. (notice that the straw is lined up on the inside of the loops)
  5. hat’s it! Now hold the straw in the middle with the hoops on top and throw it in the air similar to how you might throw a dart angled slightly up. With some practice you can get it to go farther than many paper airplanes.
  6. How does it work?

Can we really call that a plane? It may look weird, but you will discover it flies surprisingly well. The two sizes of hoops help to keep the straw balanced as it flies. The big hoop creates “drag” (or air resistance) which helps keep the straw level while the smaller hoop in at the front keeps your super hooper from turning off course. Some have asked why the plane does not turn over since the hoops are heavier than the straw. Since objects of different weight generally fall at the same speed, the hoop will keep its “upright” position. Let us know how far you were able to get the hoop glider to fly. Tell us on the Science Bob Facebook Page.

MAKE IT AN EXPERIMENT

The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:

  • 1. Does the placement of the hoops on the straw affect its flight distance?
  • 2. Does the length of straw affect the flight? (You can cut the straws or attach straws together to test this)
  • 3. Do more hoops help the hoop glider to fly better?
  • 4. Do the hoops have to be lined up in order for the plane to fly well?