Electricity Lab Part 2

We started working with electricity recently and have used inquiry to discover Ohm's Law ( V = IR ). We are going to use Ohm's Law to help us make sense of a strange phenomenon. Electric circuits seem to have a mind of their own. In fact, the way in which you connect the same objects in a circuit can have a dramatic effect. We are going to use Phet's DC Circuit Construction Simulation to explore a number of circuits. You are going to explore 5 circuits in total. For each circuit you must record in your notebook:

• Voltage of the battery
• Current through the circuit
• Resistance of the light bulb (make sure each bulb has the same resistance)
• A diagram of what the circuit looks like
• Voltage drop across each light bulb

Follow this first video to help you get your first circuit set up. You may choose any battery voltage (stay low enough to keep from blowing the circuit) and any resistance for the light bulbs (keep it low enough that the lights turn on).

In the first video the "voltage drop" across the light bulb was 12 v. Think of a completing a circuit like completing a log flume, at the end you are at the same height that you started. If the battery brought the voltage up by 12 v then we have to go back down 12 v before we get back. But how does this change when you have multiple light bulbs. Build the circuit in the second video to find out.

We have seen a series circuit before. It makes sense to think that adding multiple light bulbs to the same battery will make them dimmer because there is less energy to go around. But what if I told you that adding more light bulbs would actually make each bulb brighter? Seems crazy doesn't it? Try out the circuit in the third video.

There are an infinite number of ways to create circuits. Try building the last two circuits in the fourth video. Each combine a portion of a series circuit and portion of a parallel circuit. Don't forget to measure the voltage drop across each bulb on each circuit!

When Lightning Strikes

We have all have seen lighting at different times in our life, but what is it? What causes it? How dangerous is it?

Lets look at what lightning is first. A flash of lightning is simply an exchange of charged particles (electrons) between a cloud and the planet. In fact, this is no different than when you get a little shock on a doorknob after dragging your feet along a carpet. Friction between objects often results in stripping electrons from one material and adding them to another. This can cause things to build up a charge. Objects like to be electrically neutral, so when there is an opportunity to dump excess charge into the earth (basically an infinitely large neutral object) the charge will jump in a flash.

While we collect a charge by rubbing our rubber shoes along carpet, clouds accumulate their charge because of colliding ice particles and water droplets. These collisions knock electrons around and cause a polarization as positively charged molecules continue to rise through the cloud. Once enough negative charge accumulates at the bottom of the cloud the Earth starts to feel the effect.Things on the ground begin to have electrons pushed further way from the cloud, leaving positively charged objects on the surface. Eventually, the charge balances out by jumping across the insulating air and bridging the connection to the ground with the tallest available object.


Lightning may be incredible to watch but it is still extremely dangerous. A single bolt can contain roughly the same amount of energy as 500 sticks of dynamite! In fact lightning is responsible for about 1000 deaths every year, and many more very serious injuries. The best thing to do when you hear or see lightning is to get indoors, away from metal, and low to the ground. If you can get to one of these vantage points then feel free to sit back and enjoy the show! Whether you are checking out upward lighting, volcanic lightning, or cloud to cloud lightning.

March Madness Statistics

I have been pondering a question posed by one of our fellow students today: What is the odds at picking a perfect march madness bracket? I'd like to try to answer that using our understanding of statistics. I'd also like to talk about the odds of picking the overall winner, which is obviously much easier. Lets do that first!

There are 64 teams in the bracket, so on first glance you would think that you have a 1 in 64 chance of picking the correct team. This is assuming all teams are just as likely to win. Historical data tells us otherwise! For instance, my alma mater Bucknell is an 11 seed which historically says they only have a 33% chance of beating 6 seed Butler. (Although in 2005 as a 14 seed they beat the odds winning over 3 seed Kansas). That being said, #1 seeds are basically 100% to win the first round, so picking a 1 seed to win it all is more like a 1 in 32 shot or a 3% chance. Now for the fun stuff, lets talk about a perfect bracket!

First of all, we need to know how many games there are:
32 in round 1; 16 in round 2; 8 in round 3; 4 in round 4; 2 in round 5; the championship
That is a total of 63 games, each with two possible outcomes. This means that we can choose one of two options 63 times. The total possible outcomes is therefore 2⁶³ or 9 x 10¹⁸! This means that to pick a perfect bracket randomly is IMPOSSIBLE! Lets assume everyone in the world ( 7 billion people ) each plays a bracket randomly every year. It would still take a BILLION years worth of tournaments to to get just one bracket that is perfect. But that is with random selection and most of us can pick better than that.

Historically speaking you can predict all the first round games with 75% accuracy. This means that for the first 32 games you have a 0.75³² or 1 in 9955 chance of picking correctly. However, you still have 31 more games to pick and each of these are basically a toss up. That means you have a 1 in 2³¹ (about 2 billion) chance of getting it right from here on. However, for the perfect bracket you need to pick the first 32 AND the second 31 games correctly. All in all you are still looking at a chance of 1 in 21 trillion to put together a perfect bracket. That means if everyone in the world played every year it would still take about 3,000 years for one person to get a perfect bracket. Good luck though!

How does a plane fly?

A lot of people think Bernoulli's Principle (moving fluids exert less pressure than static fluids) is true and that it is why planes fly. First, lets make sure it is true:

If we accept Bernoulli's Principle as true, it typically gets applied to flight like this:

But if that were the case, turning the wing upside down would cause planes to drop from the sky incredibly fast (even faster than in free fall). However, this doesn't happen. For instance, planes shouldn't be able to do this:

So what is the problem? Is Bernoulli's Principle true? Is it why planes fly? Does it have nothing to do with planes? Is there something else that also needs to be considered?

Pascal and Archimedes

Blaise Pascal (1623-1662) was a mathematician, physicist, philosopher, etc. He came up with, what we now call, Pascal's Principle: Pressure is transmitted undiminished in a fluid. Basically, this means that if you push on a fluid, that push is felt everywhere in the fluid. This can be demonstrated quite easily with The Blob.

Archimedes came around significantly earlier than Pascal (287 BCE - 212 BCE) but was a similarly accomplished mathematician, physicist, philosopher, etc. He came up with what we now call Archimedes Principle: The buoyant force on a body immersed in a fluid is equal to the weight of the fluid displaced. Here is a short Ted Ed video describing how Archimedes got started working on this principle. In FACT his method could be extremely useful for you in trying to measure volume for your A assignment.

Will It Float Results

Here are some examples of different techniques used for the Will It Float Competition. Below are the results. Post as a comment the properties of the materials that were MOST useful.

1-1: 170g     1-2: 100g     1-3: 250g     1-4: 240g

2-1: 300g     2-2: 220g     2-3: 300g     2-4: 200g

5-1: 200g     5-2: 150g     5-3: 110g     5-4: 70g

Here are some extra examples of the Ideal Gas Law in action:

Liquid Nitrogen is extremely cold. Watch what happens when it is poured on top of a balloon.

Here is a demonstration of a Fire Piston in action. A sealed compartment is shrunk incredibly small very quickly. Look at the effect at around 45 seconds into the video.

Lastly, check out this video of a glass beaker being heated up to extremely hot temperatures. Eventually it is exposed to a pool of cool water, you'll be shocked with what happens!

BAM - B Thermo and Fluids Help

Pressure and Ideal Gas Law

Do you feel that? On your shoulders? That weight? About 1200 lbs. Right now there is about half a ton of air sitting on your shoulders, pressing you down. Before you start thinking that you are a beast and can squat way more than you thought, you have to be aware that we can't really feel this weight, or at least we are used to it. That doesn't mean that its not there. In fact, that weight of air can be used to crush a 55 gallon steel drum.

Not impressed? What if I told you that air could even crush a train? Don't believe me... Go ahead, watch this.... I'll wait.

Air pressure, or the force exerted by a gas trying to expand, can be incredible. We are already pretty familiar with this idea with water pressure. Ever try to swim to the bottom of a pool? This is what is happening to your chest and ears.

The questions remains though: Why does this happen? Or, why don't things get crushed all the time? To answer that we'll need to understand pressure and the ideal gas law. This tells us that there is a relationship between temperature, pressure, and volume. But if that is the case, pressure should be able to do more than just crush things, right? Kaboom.

Here are some specifications for each scenario so we can do some investigation of our own. Assume that each example took place at 1 atmosphere of pressure: 1.01 x 10⁵ pa.

55 Gallon Drum: 23 in diameter, 35 in tall.Assume no interior pressure.

Train Car Dimensions: 6.1 m long, 2.6 m high. Assume no interior pressure.

Hot Water Heater Dimensions: 22 in diameter, 30 in height; Interior Pressure: 2.3 x 10⁶ pa.

Some Thoughts on Heat

We just started thinking about heat energy (Q) again so I thought I would share a shot from our diagram on the board and a few thoughts. When you add energy to something (any kind of energy) that something changes. If I add a Big Mac to you, you gain weight. If I add kinetic energy to you, you start moving faster. If I add heat to you, you get hotter.... sometimes. We really get two choices every time we add heat to something: 1) Change Temperature or 2) Change State. Take a look at the diagram below.

When we add heat to ice, it wants to get hotter. However, it gets to a point (Melting Point) where it can't get any hotter as a solid, at that point it begins to convert to a liquid, which also takes energy (Heat of Fusion). Once all of the solid has converter we can get hotter again, until we hit another boundary (Boiling Point). No we must use energy to convert to a gas (Heat of Vaporization). At that point we can keep going up (and eventually become plasma.

Although turning ice into steam can be energy intensive and seems tough, its a problem made up of lots of simple steps. Take the example in the graph above, converting 1 kg of ice at -30oC to steam at 120oC. Although it takes 5 different stages of adding energy, each step is pretty simple.

This is kind of unrelated, but I thought you'd enjoy. Here is a video of some experiments with dry ice and a microwave:

Light and Sound Review

As promised, here is a video review of ALL of our light and sound topics. I hope that it helps you prepare for our quiz!

Superposition and Sound

So I happen to be in the chorus room for parent teacher conferences and figured this would be a great opportunity to do a demo with sound that I have been meaning to get to. The video has to do with the superposition of waves using a guitar. This image represents a whole bunch of possible standing waves that can take place on a string of length L.

When you play a note on a guitar you are making these waves, but they all happen at the same time. Imagine adding all of those waves together, the resulting interference is referred to as superposition. Check out this video I made demonstrating the idea of superposition: multiple waves existing at the same place at the same time.

BAM - Periodic Motion

Here is a brief video giving some guidance about the B assignment for periodic motion, in particular question 3.

   

Although this is a repost from my twitter stream, it illustrates the difference in period between pendulums in a beautiful way.

This professor helps to explain resonance and then gives a wonderful simple demonstration. He does some calculation practice for pendulums first as well. Note that in his calculations he is solving for FREQUENCY instead of PERIOD. This means that his formula is flipped upside down compared to ours. The demo he uses is a great illustration of resonance!

Behold the power of resonance! This is video of the Tacoma-Narrows bridge from the 1940's. Every object (pendulum, rocking chair, slinky, even bridge!) has a natural frequency, or rate at which it prefers to vibrate. If you help push it just right (resonance) you can get an effect like this.

Roller Coaster Design

These three videos were created by a mechanical engineer working with the Skate Park simulation to help demonstrate some of the features that might be helpful for your design.

Design Help

Analysis Help

Incorporation of Friction Help

Niagara Falls

Over Christmas break Mrs. Quinn and I went on a road trip that took us into Canada and by Niagara Falls. I have never been before and was blown away by the magnitude of it all. Here is a picture I took from the room that we stayed at:

To the far left are the American falls and to the right is just a small portion of Horseshoe Falls on the Canadian side. I had seen them in pictures before but never up close. Horseshoe Falls in massive, unbelievably massive. Here is a short video of Mrs. Quinn and I standing right by the edge on December 26th.

We eventually made our way down behind the falls into a small tunnel that had posters talking about some of the details about how the falls had changed over time, famous visitors, and how much water actually goes over each minute. I took these two pictures for you guys because they have interesting information about the falls:

 It seems that over a century ago other visitors to the falls realized that not only were the falls beautiful to look at, but they were incredibly powerful. They developed ways to take energy from the falls and use it to power local towns. In fact, when I was there a new tunnel was being built to make the power plant even better and more efficient. In total 750,000 gallons of water go over the falls every second! 1 gallon is 0.0037854 cubic meters and 1 cubic meter of water is 1000 kg. With that information could you determine how powerful the falls are? Since there is a restriction as to how much water could be generated for power, what is the maximum amount of power that is actually generated? For comparison sake the maximum output of an 18-wheeler is 450 kW.

Niagara Falls is famous for daredevils going over in barrels. What I found out when I was there is that the first person to ever attempt/survive this feat was a woman name Anne Taylor, pictured below. I was also amazed to find out that she 63 when she made the attempt!

 Based on the height of the falls, can you determine how fast she must have been moving when she landed? Anne survived,but many others have not been so fortunate. In fact, since 1850 an estimated 5,000 bodies have been found at the bottom of the falls. The falls are another great example of the power, beauty, and potential danger of the natural world.