Conservation of Energy: Your Own Astroblaster

You may have seen one of these toys around... A stick with 5 bouncy balls staked on top of one another.  You drop it on the ground and the top ball goes flying sky-high.

You can do your own demonstration, on a larger scale with balls you probably have scattered around your house (or that you could borrow from the phys. ed. teacher).

I'm using a squishy mini-soccer ball stacked on a basketball.  They're both a little flat, and only bounce up to about my waist when I drop them from chin height.

But, if I stack them on top of each other and drop them, the soccer ball goes flying off, reaching an altitude many times higher than when dropped by itself.  The basketball doesn't bounce back much at all.  Just a little, and then it rolls away. 


The soccer ball went much higher than that - my camera timing skills aren't perfect!


This is a demonstration of conservation of energy and momentum.  Nearly all of the energy the basketball had is transferred to the soccer ball - allowing the soccer ball to fly off with more energy than it started with and the basketball, left with almost nothing, just rolls away.

You can have lots of fun experimenting with different balls - golf balls, ping pong balls, super balls, playground balls, etc.  What do you think would happen with 3 balls?  Give it a try!

Energy: Nuclear Fission Demonstrations

While we're on the topic of explaining nuclear energy, you can find some recorded nuclear fission demonstrations on YouTube. I know many schools have blocked YouTube, but I hope it's still useful to some of you.  

My favorite video comes from Touchstone Energy.  While not recorded for scientific purposes, the sheer size of the demonstration is impressive.  You'll have to ignore the sales pitch, but it's non-offensive and pretty short. 



And, just for fun, here's another commercial video along the same lines. 

Energy: Understanding Nuclear Energy

I may be a bit late in getting this to you, but hopefully it's useful to someone out there....

In light of recent events in Japan, or just in the course or your curriculum, you may be looking for ways to help your students understand nuclear energy. 

I just stumbled across this publication, Nuclear Experiments You Can Do, from the Charles Edison Fund..

The pdf file includes simple models/demonstrations for splitting an atom and chain reactions, as well as more
advanced demonstrations related to nuclear energy and radioactivity.

I wanted to pass this your way as quickly as possible, since it is a timely topic.  As a result, I haven't looked through the other experiments available, but they could very well be worth taking a look at.

Glue Stick Magnifying Glass

Did you know a clear glue stick (for a hot glue gun) can be used as a magnifying glass?  The way the light bounces around the cylinder and refracts because of the change in material causes the glue stick to act as a lens.  Lay it over some small type and see how much larger it appears. 

Some other objects that can be used in the same way:
--a glass stirring rod
--a test tube filled with water (sealed with a stopper)

Layered Water

This is a lovely demonstration of the way water's density differs with temperature and convection currents (you don't actually see the currents, but you see the end result).

Allow a pitcher of blue-colored water to cool in the refrigerator overnight. 

At demonstration time, prepare a pitcher of hot tap water.  Color this water yellow.

Fill a jar (or cup) all the way with blue water.  Fill an identical jar all the way with yellow water.

Place an index card on top of the blue jar.  Carefully turn the jar over and set it on top of the yellow jar - make sure the rims line up.

Ask for hypotheses as to what will happen when you slide the card out.  Slide the card out -- the blue water sinks, mixing with the yellow, creating green water.

Now try again....
Prepare the jars in the same way.  But, this time, place the index card on the yellow jar, and place the yellow jar on top of the blue jar.

Remove the card and watch.....

You'll get a little green water right at the interface, but the yellow and blue water will mostly remain separate.


Why did you get two different results? 
Cold water is denser than hot water - it sinks.  When the cold water was on top of the warm, it sank to the bottom of the vessel, mixing with the warm, as evidenced by the mixing of colors.

When the cold water was on the bottom, it was content to stay right there.  Just a little mixing occurs right where the two temperatures meet.  What do you think would happen if you allowed it to sit for awhile?  Would the colors remain separate, or would they eventually mix?

Light: Seeing Color

[The nature of this activity makes it difficult to photograph (at least for one with limited skills in that area, such as myself).  Try it yourself for the best results.]

A little refresher on color and light...
--White light is composed of all the colors in the spectrum (red, orange, yelllow, green, blue, indigo, violet).

--An object appears red because it reflects the red light and absorbs all the other colors.
--An object appears white because it reflects all the colors in the spectrum, and absorbs none. 
--An object appears black because it absorbs all the colors in the spectrum, and reflects none. 

What you'll need...
--a red toy car
--a blue (or other non-red color) toy car
--a red light (this could be a laser pointer - be careful!, a filtered flashlight, a toy - mine came from a cereal box)


You'll need to do this demonstration in a darkened room.  If you can't get your room dark enough, you can set it up inside a large cardboard box - but only a few people will be able to view it at a time.


To perform the demonstration...
Before darkening the room, show the students the two cars, so they can see that one appears red and the other blue.

Turn off the lights.  Shine the red light on the red car.

The car will still appear red because it is reflecting the red light (it's not absorbing anything since you didn't shine any of the other spectrum colors on it, but that doesn't change what you see).

Now shine the red light on the blue car.

The car will appear black (or at least a dark shade - to get black you'd need a totally dark room and a pure red light).

Here's why... 
Your light is only emitting red light.  The blue car only reflects blue light.  There is no blue light for the car to reflect.  The red light is being absorbed by the car.  The result, for our eyes, is black, or the absence of color.

Convection: Shavings in Boiling Water

Fill a larger beaker with water.  Empty your pencil sharpener into the water.  Give it a stir to mix in the pencil shavings (some of them will still float - that's okay).

Place the beaker on a hot plate and turn it on.  The beaker needs to remain on the heat source throughout the entire demonstration.

As the water gets hot, the pencil shavings will make the normally invisible convection currents visible.

The water at the bottom of the beaker is heated.  It then moves to the top of the beaker and the cold water sinks to the bottom of the beaker.  This water is then heated and moves to the top and cooler water sinks to the bottom.  This continues on and on, first heating all of the water, and then maintaining a consistent temperature.

Convection: Spirals over a Lightbulb

For this demonstration, you'll need a functioning lamp, shade optional.
You'll also need to cut a spiral out of construction paper and add a string so you can hold on to it.

FYI: This spiral was WAY too long (or my arm is way too short....) - I cut about half of it (the spiral, not my arm) off. 

First, hold the spiral above the lightbulb with the lightbulb off. The spiral will pretty much just hang there (it might spin around at first, if your string was twisted, but once it's settled, it should stay put).

Then turn on the lightbulb and hold the spiral above it again.  This time, the spiral will spin, and continue to spin. (I realize the picture below is useless, as you can't see it move, but it is, I promise). 

The lightbulb is heating the air above it (a by-product of converting electrical energy to light energy).  The warm air rises and cooler air sinks - a convection currect.  This moving air spins the spiral 'round and 'round.

Half-Life: The Penny Model

If you're introducing your students to the concept of half-life, things are probably seem a bit fuzzy for them.  Let them get some hands-on experience and see if things don't come a bit easier.

A quick review for anyone who may not have done this in awhile...
...half-life is the amount of time needed for half of the atoms in a sampleof a radioactive isotope (one form of an element) to deacy, or reach a stable state.  Some isotopes have half-lives that are a matter of seconds - they decay and become stable rapidly.  Other isotopes have half-lives that are thousands of years. 

Now, on with the show!

Start with 100 pennies.  Put them all in a cup, place your hand on the top and shake.  Dump the pennies out onto the table.  Remove all of the pennies with heads up (or tails, it doesn't matter, just pick one and stick with it).  Count and record the remaining pennies.  You have just completed one half-life.  Repeat until you are down to one or no pennies. 

Have students graph their data.  It's always good to practice graphing, and it helps some students visualize what's happening (and the graph for half-life will always take the same shape - the numbers and units on the axes may change, but the shape of the curve is always the same).

Now you can pose some questions to your students....
If someone walked by and saw that you had 7 pennies remaining, could they determine how many half-lives (shakes) you had completed?  How? 

And then take it into the real-world application of carbon dating....
Imagine that while digging in your yard, you uncover what appears to be a very old bone.  Through the help of a scientist at the lab, you're able to learn that the bone contains 12 pug (picomicrograms) of carbon-14 and that it contained 100 pug of carbon-14 when it was buried.  Carbon-14 has a half-life of 5730 years.  How old is the bone. 

P.S.
I did come across one criticism of this activity online, and I thought it was worth mentioning.  This person suggested that you needed to replace the "decayed" pennies with something else, because they decay, they don't disappear.  I thought it was a valid point, and in thinking about it was a little surprised that I've never seen that mentioned as a part of the activity. 

I'm thinking the small counting chips that you might have for games of bingo would be great - a similar size but definitely different from pennies would work great.  Kernals of popcorn would also be an inexpensive item to use.  Let me know if you think of something else. 

P.P.S.

If your students have been super good (or it's immediately following Halloween and you have a plethora of left-over candy), you could also complete this activity using M&Ms or Skittles. 

Potential & Kinetic Energy: Jumping Frogs

Have students fold origami jumping frogs using green index cards (the color really doesn’t matter, just makes it more fun). Allow students to play with the frogs and have them explain at which point the frog possesses 100% potential energy and at which point it possesses 100% kinetic energy.



Make sure you try your hand at making the frogs before presenting this lesson to your students. It's not hard to do, but you'll be much more effective at helping students if you've done it yourself first!