Detective Day: Lifting latent fingerprints

You know how to be a spy, to write in code and see what wasn't meant for your eyes.  But not everyone in the shadows is a friend.  There are those who dwell in the shadows for reasons other than country and honor.  Those who pass through like a wisp of smoke, taking what is not rightly theirs and leaving nothing behind.

Or do they?  Perhaps they left behind more than sorrow.  To find out, we can learn from those who work on the other side of the law, who make it their business to find the dastardly who work in secrecy, and bring them forward to society to answer for their crimes.  The tough, the ruggedly intelligent who always know where to look.  Detectives.

One of the oldest and most important clues is still used today--fingerprints.  Nobody has exactly the same fingerprints, not even identical twins.  People leave fingerprints wherever they touch something without gloves--when the fingerprints are invisible to us, they are called latent fingerprints. Detective are experts in finding and lifting latent fingerprints.  "Lifting" is the processes of transferring the fingerprint from the surface where it's found to something it can be stored and studied on, like a card.  Surprisingly, you can lift fingerprints with household items it almost exactly the same way professional detectives do.

You will need:
Either very dark fine powder (like graphite or black eyeshadow) or very light fine powder (I used flour).
A very fine brush with soft bristles.  I recommend a makeup brush, like someone in your house might have for blush.
Clear packing tape
White index cards
Dark paper (you only need this if you have light powder)

Supervision: dusting for fingerprints takes a certain "knack."  This project is best for older girls (junior high and up) or younger girls with a supervisor with the knack.

First, find an area to look for fingerprints.  The best surface is reflective and smooth, and a solid color.  Ceramic mugs and plates, microwave buttons, doorknobs, and counter tops or desktops are often good places to look for fingerprints.  Choose a surface that contrasts with your powder (i.e. a white surface for black powder and a black surface for white powder).

Sprinkle your powder and very, very lightly dust off the powder with your brush.  I found light motions with the side of my brush worked well.  You may want to start by cleaning a patch of surface and putting your own, clear fingerprint on it.  Dusting that will give you an idea of what to look for.  You may find palm prints, which detectives also use.  The powder gets caught on the fingerprints because when you touch something, natural oils from your body are left behind that have been pressed into the shape of your fingerprint.  The oils stay there, and catch the powder.  To lift the fingerprints you've dusted, lay a small piece of packing tape carefully over the fingerprint, sticky-side down.  Press it down, but don't rub it, and try to avoid air bubbles.  Then peel the tape off, and stick it onto the card.  (If you used white powder, stick it to dark paper so it shows up, and then cut out the print to put it on the card.)  You can categorize your prints by writing the date and time, place it was collected, person who collected it, and material used.  This is the sort of thing detectives write.  They will need all of this information not only to catch the criminal, but to have in court to convince the jury they caught the correct person, and legally.

If you like, you can try to characterize the fingerprint you lifted, and maybe, if you get prints from people who have been in your house, like your family, you can compare the print you lifted to theirs and figure out who originally left it.  The FBI has information on the different features to look for in fingerprints here.  For example, my left thumb has a plain whorl pattern, and my right thumb has a double-loop whorl.  My fingers have mostly loops and arches.  How about yours?  How about the prints you lifted?  You can list these characteristics on you cards as you analyze your prints.  Good luck, and have fun!

Mini Monday: Kazoo

Hello girls!  Today, we are going to use the science of sound to make our own kazoos!

You will need:
A cardboard tube, from used-up toilet paper or paper towels
Wax paper or brown parchment paper
Rubber bands or tape

No adult supervision needed this time!

We're going to use the kazoo to amplify (make loader) some of the sounds you make when you hum!  And it's easy as pie.

First, cut a square of wax (or parchment) paper that is about 5 inches wide.  Wrap it around one end of the cardboard roll, and hold it in place with the tape or rubber band, just like in the picture at the top of the page.  Now, just before the rubber band or tape, poke a small hole in the cardboard tube, only about as big as the tip of your pencil.  You can use the tines (those are the long pointy parts) of a fork to make the hole.  Don't cut the paper, just the tube--we want a way for air to escape so you can keep blowing!

Your kazoo is ready!  Put it right up to your mouth and hum into the inside of it.  It also works to say things with a low voice, like "doo da da dum doo."  Does it work if you use a high, or squeaky voice?  Not really.  What's happening here? 

Well, remember how the kazoo only amplifies some of the sounds you make?  That's because the paper has a resonance--a certain kind of sound that makes it vibrate.  Sound happens with parts of the air gets squished together very close.  Lots of times, that happens because something is vibrating--which really means it's hitting the air over and over again really fast, and the air squishes a little whenever it gets hit.  The squished air reaches our ears, and our amazing ears can tell our brains what kind of sound it is!

So when the paper on the kazoo vibrates, it amplifies the sound you made and makes sounds of its own!  For the paper, the resonance is low-sounding humming sounds--so it doesn't vibrate when you make high-pitched noises, but it vibrates a lot when you make low-pitch ones.

Now that you know how to work your kazoo, enjoy humming your favorite songs into it and seeing how silly they sound!

Block and Tackle

Girls, I have a problem.  I've just bought some delicious ice cream--but the bowls and spoons are in an apartment on the third floor; on the second floor, right next to the stairs, my friend is studying with the door open.  Doesn't sound like a problem?  Well, it is!  My friend loves ice cream.  She loves it so much, when she sees it she cannot rest until she has eaten every last spoonful.  If she sees me going  past with ice cream, I will never get to taste so much  as a bite!

Well, how should I solve this?  I could sit outside and eat the whole gallon of ice cream.  I could try to smuggle it under my shirt, or give it a disguise.  I could do any of those things, but I am a scientist and an engineer!  I have wit!  I have determination! I have a block and tackle attached to my window!

Ice cream disguised as a simple newspaper delivery girl

Yes, a block and tackle!  These marvelous inventions are made when more than one pulley combines forces. Pulleys are little wheels, except instead of tires they have a dip (or groove) all the way around the edge.  A rope fits into the groove, and you can use the rope--with pulleys--to lift something with less work.

Today, we're going to make a block and tackle just like mine.

You will need:
Two empty spools
Two wire coat hangers
String (thick)

No adult supervision required!

First, the hardest part: we need to unwrap the wire coat hangers, and bend it flat enough for us to slide on a spool.  Once you've slid the spool on, bend the wire so it can't fall off.  One way is in the picture below, but there are lots of ways for this to work.

Do you have both hanger-pulleys ready?  You are ready to set up your block and tackle!  There is lots of weaving around, so it can get complicated.  Just follow the diagram below as closely as possible:

You are ready to hoist up your load!  (My load was ice cream--but yours can be whatever you like!)  This pulley makes the ice cream feel half as heavy as it actually is--but, you have to pull twice as much string (see how the string goes all the way up to the window and back down again?).  In fact, a pulley is one of the six simple machines--a group of the the most simple devices that change the direction or amount of force.  My force here came from the weight of the ice cream, and one of the things the pulley did was change the magnitude (total amount) of that force that I had to pull up.

Ice cream ascending

Almost there!

Sweet victory

Like the idea of pulleys?  You don't have to stop with hangers and spools--you can buy actual pulleys at stores that sell boating supplies, and set up a block and tackle to your window or a tree house that will be strong and sturdy and last for ages!  Those pulleys are strong enough for you to attach it to a swing seat, and actually pull yourself up!  That would be the coolest tree-house entrance ever--thanks to pulleys!

Mini Monday: Convection

Hello girls!  Once again, FSG has returned to one of our favorite things--swirling colors!  This time, we are going to use heat and convection to make our colors mix.  Have you ever been baking something, and when you open the oven a blast of hot air comes out?  How could that happen?  There wasn't a fan in the oven!  The secret is convection.

You will need:
A pan full of liquid (I used milk so the colors would show up really nicely, but you can use water too)
Food coloring
A stove

You will want adult supervision, so that it is safe to use the stove.

Do you think liquid can move, even if nothing touches it?  What if you heated it up? Maybe you think it would only if it was boiling.  But here's a secret of the science world--heat is energy!  In fact, the coldest thing in the world could only happen if nothing, not even the tiniest atom, moved at all--not even a twitch.  You absolutely could not get any colder than that--in fact, that temperature is called absolute zero, and even the best scientists with the best technology in the world can't get anything quite that cold.  If you add heat, you're adding energy and particles can use that energy to move.

Now that we know this, we can guess what will happen if we heat up a pan full of colorful liquid--and we can guess that it's going to look pretty cool!  Put your pan full of liquid on the stove, then let go and don't touch it for 30 seconds.  Now we know it's perfectly still, and we can carefully put a few drops of food coloring near the middle of the pan.  They mostly stay where you dropped them.  Carefully turn on the stove and step back.  Even though you're not touching it, and even when it's not boiling yet, the liquid will start to move, pulling the food coloring with it!  That's convection--heat kicking fluids into motion!

Rubber Band Gun

Today we are, hem, studying the conversion of potential energy to kinetic energy.  With our very own rubber band guns!  Erm, it's all going to be very educational.  Very educational indeed.

Be sure to emphasize this point if an adult tries to confiscate it from you.  "But Dad!" you should insist, "How will I ever learn about the conversion of potential energy to kinetic energy?"  All the same, don't take this project to school!

For this project, you will need:

A short, fat stick
A nail
A clothespin
Strong glue or epoxy

You will definitely need an adult for this project!  Hammering a nail through a stick--even a thick one--is difficult to do without the nail splitting down the middle, so it's smart to have someone experienced do it or show you how to do it--and you need supervision for safety, too.  The nail only needs to just barely poke out of the other side of the stick.  Farther down the stick, glue the clothespin.  Make sure the end that opens faces the nail.  It should look like this:

Once everything dries, you're ready for the demonstration of potential and kinetic energy! Clip one end of a rubber band in the clothespin, and slip the other end over the tip of the nail.  The rubber band now has potential energy because it is not actually moving, but it is stretched out: the rubber band's stretched-ness puts a force on it that gives it the potential to move.  This potential can be converted to kinetic energy, energy in motion, if you open the clothespin and release the rubber band at your target.  You will probably want to repeat this scientific demonstration choosing many targets--although don't expect a brother or sister not to fight back if you choose them! Just ask my mom, who made these exact rubber band guns when she was a kid!

Mini Monday: Momentum from bouncing balls

Hello girls!  This Monday's project is as easy as it is fun.  I hope Spring is in full bloom where you are, because this is a great project to do outside--but it can be really fun inside as well, especially with ricocheting (flying into something and bouncing off in a crazy new direction).  Has that piqued your interest?

We're going to use a tennis ball and a basketball to demonstrate the power of momentum.  You don't need adult supervision for this one--but you will want permission before you do it inside!

If you don't have a basketball, that's okay--you can use any big, bouncy ball, like a red playground ball.  You can also use any small bouncy ball instead of a tennis ball, like a ping-pong ball.

First, hold both balls straight out in front of you, and drop them at the same time.  Hey, you might ask, where's that ricocheting you promised?  Don't worry, it's coming--this was just to show how high the balls normally bounce, without an extra boost from momentum.

Now we use a little bit of momentum.  Hold the basketball right on top of the tennis ball, and release them at exactly the same time.  What happened?  Did the tennis ball not bounce at all, while the basketball bounced a little higher than where you first dropped it?  That happened because instead of bouncing itself up, the tennis ball transfered (gave) all of its momentum to the basketball, and the basketball bounced higher because of the extra momentum from the tennis ball.

What do you think will happen if you drop them with the tennis ball on top of the basketball?  Try it out--but you might want to tell anybody watching to duck first!

Whoa there!  Not exactly the same, was it?  The tennis ball shot off and went way higher!  But why?  Actually, the same thing happened as before--the ball on the bottom gave its momentum to the ball on the top.  But momentum is tricky.  The faster something is going, the more momentum it has--but it also has more momentum the bigger something is.  Since the basketball is so much bigger than the tennis ball, adding the tennis ball's momentum to the basketball only makes it go a little higher.  But adding the basketball's momentum to the tennis ball makes it shoot off, going as much as nine time higher than it did before!  Try getting somebody really tall to do this--then the tennis ball will really soar!

Lemon Electricity

Hi girls!  Today's project is a classic, and for good reason. Generations of girls have marveled at the coolness of making their own battery--from lemons!  This is no gimmick or trick--we will literally use lemons to make enough electricity to light up an LED!

For this project, you'll need:

Lemons, of course! (have as many as ten, maybe even more, handy)

Galvanized steel paperclips (if you don't have galvanized steel paperclips, try filing or sanding off the outside of pennies, until they look silver--they're mostly zinc, and will work even better)

Copper wire

An LED (you can get them at Fry's or Radioshack, or maybe even pull them out of an old toy or broken electronics)

You might want an adult for this experiment, just to cut notches in your lemons.  There won't be enough electricity to shock anyone, so no need to worry about that!
First, roll around the lemons in your hands and squish, squish, squish 'em!  We do this so that all the lemoney juice (especially citric acid!) inside is free to move all around the lemon.

Now, cut your wire into the same number of pieces as you have lemons.  Wrap one end of each wire around its own paper clip.  Make sure the part you wrap around the paper clip isn't insulated--if it is covered in plastic, it can't conduct electricity!  Electicity is make of electrons shooting along something--but electrons in some materials, like plastic, just won't move--these materials are insulators.  Insulators are nice when we don't want electricity flowing through us--we just keep insulators between us and the electricity.  But when we do want electricity, like for our lemon battery, we don't want insultors blocking it, so we peel them off.  Go ahead and peel the insulation off both ends of each copper wire.  Metals like copper and gold are conductors--electrons can whiz along them, no problem.  We say these materials conduct electricity.

Okay, now cut two small notches about an inch apart on one of your lemons.  Be sure to cut all the way through the lemon's skin and into the guts.  Take the end of the paper clip that isn't wrapped in wire and stick it into the lemon.  Now, take a new wire and stick the end without a paper clip into the other notch in the lemon.  Think nothing happened?  Leave the wires in the lemon, and stick the other two ends on your tongue.  That's the taste of electricity!  Your lemon is a battery!

It's not good enough to light up the LED though...not yet.  Take the paper clip hanging off your first lemon--the one that's not actually inside it--and stick it in a new lemon.  Take a new wire, and stick the non-paper-clip end in your new lemon.  Now your battery has the power of two lemons instead of one!  Try to light up your LED by touching the two prongs poking out of it to the two wires coming out of your double-lemon battery.  If it doesn't work, switch which wire touches which leg.  Still doesn't work?  Keep adding lemons!

One lemon battery after another!

If you've added more than nine lemons and it's still not working, we need to troubleshoot, or figure out what's wrong.  First, try it in the dark--maybe your LED is very dim.

Next, it's likely that your paper clips just do not have enough zinc in them.  (We'll talk about why zinc matters in the next paragraph.)  Mine weren't working, so I tried using "steel fastener bases" from Staples.  These worked better, and in the dark I could see my LED had lit up.  Success!  Science is often about things going wrong the first time (and maybe the second and third times too!).  Pennies with the coppery outside sanded off would work even better--if you use them, you probably won't have any troubles.


My lemon battery still wasn't working!

I switched the paperclips for steel fastener bases, and it worked!

So, what's going on here anyway?  Are lemons electric?  Nah--it's just chock full of acid.  Citric acid, as a matter of fact!  We put two different kinds of metals in the acid of the lemon--the paper clip, and the copper wire.  The paper clip is galvanized, which means it has a shiney surface coat that has zinc in it.  Zinc is the player we want!  The copper wire has--well, copper.  In the citric acid, zinc is oxidized, which means some of its electrons fly off.  Now, what did we say electricity is made of?  Yup, flying electrons!  The extra electrons fly right on up the copper wire, and there you have it.  A normal old fruit makes electricity!  Real batteries work just the same way.  That's way it's so incredibly dangerous to swallow batteries, and they have to be thrown away in a special garbage--they're full of acid, and it's much more dangerous acid than the kind in lemons.  But don't worry; as long as they aren't leaky, batteries aren't dangerous.  Just take them away from toddlers so they don't chew on them!

Mini Monday: Plasmolysis

Hi girls!  I hope you all had a splendid weekend and are ready to start the week with a Mini Monday!

We all know that flowers need water to stay happy and pert after they're put in a vase.  But what if it's not just water--what if we add something else?  Well, we're going to find out!

You need:
Three flowers
Three cups
Salt
Sugar
Masking tape + marker

No supervision required!

Fill each glass with the same amount of water--you only need a few inches.  Now, set one aside.  Use the masking tape and marker to label that one "Water."  Take the next glass and pour salt into it a little bit at a time, stirring.  Keep adding salt until it doesn't disappear anymore, and some just sits on the bottom.  Label this cup "Salt."

Now, stir sugar into the third cup.  Lots and lots of sugar will dissolve--much more than salt--so the water might try to trick you, and pretend it can't hold anymore--but it can!  Keep pouring sugar and stirring it all away until it really won't hold anymore.  Label this one--you guessed it--"Sugar"!

Put a pretty (or ugly, really, it's up to you) flower in each cup.  What do you think is going to happen to each flower?  Which one will stay the strongest and stoutest?  Which will wilt the fastest?  Write it down before you read what happened to my flowers--no peeking!

After a few hours, what happened to your flowers? What happened after a few days?

You might have thought the sugar-water flower would do the best--maybe the flower would like to eat the sugar!  And it did do better than the salt-water flower, which was the first to wilt.  But the hero flower, the flower that persevered (kept going without giving up) through it all, was just plain water.  Why?

Well, there's the question!  Is it because sugar and salt are bad for you?  Well...no, probably not.  Do you remember a Mini Monday of old, Eggy Osmosis?  In that Mini Monday, we found that chemistry always wants to create an equilibrium, with the same amount of stuff per water everywhere.  Well, there's a lot of water in healthy flowers--but not a lot of particles like salt.  When we stick it in water filled with salt, the water in the flower tries to balance things by flowing out of the flower and into the cup, diluting the salt or sugar so that there's more water for the same amount of salt.  It does the same thing for sugar.  When water is pulled out of plant cells, it's called plasmolysis: with no water to hold it up, the flower bends and wilts.

Maybe you've had a teacher that put one flower in water and another in soda.  When the soda-flower died first, he or she might have said soda is unhealthy, and so the flower died.  Well, that was just a dirty trick! Now you can tell your teacher, "No, no, no! It's just osmosis!"  (Soda isn't good for you, but it's not going to make you shrivel up!)

The flowers on the first day.  Salt is on the left, water is in the middle, and sugar is on the right.

This is what the flowers looked like only one day later. Sugar is on the left, salt in the middle, and water on the right