# Monthly Archives - August 2011

## Accelerate Student Interest with the Newest Bottle Launcher!

Bottle rocket launchers can be a great way to increase interest as your class kicks off this Fall. We’ve collected some tips for how to get more out of these rocket powered demonstrations and launch your students into the world of force and motion in full Cool Stuff fashion.

Hold a friendly contest to engage interest in what affects the behavior of the bottle rocket during flight. Form the students into groups and then provide them with a variety of cardboard tubing options and some extra cardboard to cut out fins. Actual construction of the rocket may be something you have them do outside of the classroom. Don’t jump into the Physics quite yet. Just challenge them to discuss and consider a variety of elements when constructing the rocket, such as length, size of fins, weight of rocket, amount of water in the rocket, and amount of pressure used during the launch (not more than 40psi of course!). Then hold a contest where the goal can be to see which rocket stays in the air the longest, which one reaches the highest, which one can carry the most weight, or which one provides the most accuracy in landing closest to a specific spot. We’ve found that the duration of flight is the simplest activity to measure, but we’ve provide some suggestions below if you would like to introduce altitude as well. After the results are in, now you have a perfect opportunity to turn their interest into an engaging discussion about force and motion, describing what elements resulted in the various outcomes and why.

The primary factors for improvements in speed and stability are the different levels of pressure, the amount of water in the bottle, the overall weight of the bottle, the length of the rocket body, and the addition of fins. With all of these variables, your students can experiment for hours, using this hands-on activity to gain a deeper understanding of a variety of core force and motion principles. For example, note the relationship between the amount of water expelled and the altitude reached. By throwing water in one direction, the rocket is thrown in the opposite direction. According to Newton’s Third Law, water and rocket should have equal and opposite momenta. How is this observed with this real world activity? Other observations that you can make include testing the bottle without water (using only air) or adding more water in the rocket than the air can expel.

Note about safety: The launcher shown in the video, the Super Bottle Rocket Launcher, has a safety valve to limit the pressure to 60 psi. The other launchers that Arbor Scientific carries do not have this feature. Please be sure to take precautions to always use a pump with a pressure gauge and do not exceed 40 psi. And of course, always make sure the bottle rocket launching base is firmly in place and not pointed at anyone. Other safety precautions include setting it up away from buildings, other structures, trees, telephone wires, and cars (when using the bottle rocket launchers in a parking lot). It must always be launched straight up in an area with no overhead obstruction. This can be a very fun and safe activity, as long as you take the proper precautions!

How to Measure the Altitude
As we mentioned, duration of flight is really the simplest way to provide a more accurate comparison of bottle rockets. Altitude is another great option, but there are some limitations to be aware of, especially when doing this in a contest setting. Depending on how you measure the altitude, it may be difficult to obtain precise measurements. For example, if you are measuring the altitude from one ground position, you may have less accurate results due to the horizontal movement of the rocket as it launches, which can vary based on which test you are running affecting where the actual rocket launch base is (which effects the altitude equation when using the angle and the distance to the base). Teachers have found success with having multiple students taking the measurements at each ground location, throwing out measurements that were obviously wrong and then averaging the rest. You can also measure altitude from multiple ground locations equidistant from the rocket launch base (launch pad), such as opposite sides of the bottle rocket launch pad. That allows you to factor for horizontal movement more accurately. With this method, you’ll need a sheet of graph paper with a chart that places the bottle rocket launch pad in the middle and then you mark down on the x-axis how far the first group is from the base. The altitude will be measured vertically (in the y-axis). The second group should be the same distance in the opposite direction. On the chart, this is represented on both ends of the x-axis. You’ll need a way for the students to measure the angle of the bottle at its highest point.

Note: Arbor Scientific’s Altitude Finder provides an easy way to measure the angle that a bottle rocket reaches at the top of their flight.

Once both groups have come up with a consensus of what angle they measured from their ground location, you can then transfer these angles to the graph using a protractor. Where they cross will tell you how high the bottle went based on the y-axis.

Here is an example of the chart with further instructions that you can use to measure altitude with two groups of students:

If doing this as a contest, even a friendly one, it is helpful to take these extra measures to ensure the fairness of the competition.

For a way to measure altitude that involves slightly more complex mathematics, you can create your own rocket altimeter. You will need to mount the chart we provide on a sheet of cardboard with a plumb line attached to one corner. Below, we provide a set of thorough downloadable instructions that includes the worksheet that is used for measurement and how to calculate the altitude based on your measurements. Simply print off as many copies as you need of the last page of this document:

Altitude Measurement Instructions and Measurement Worksheet

Note that you’ll need a piece of cardboard to attach to the back of each sheet you use for measuring altitude. You may want to create more than one for a larger class. You’ll also need a common pin (for poking holes in the cardboard), a string to use as a plumb line, a piece of tape for securing the string, and a weight for the end of the string (typically a large washer). You might also want a soda straw to use as a sight tube.

Unfortunately, this method does not account very well for horizontal movements of the rocket and cannot be combined with measurements from different vantage points, making it somewhat inaccurate when using in a contest setting. Therefore, we recommend to only use this approach when demonstrating the mathematic principles it uses while gaining a general sense in the difference between using different variables.

## Products

### Super Bottle Rocket Launcher

The one piece bottle rocket launcher that can launch a 2-liter soda bottle up to 100 feet! What better way to provide students with a real-world application of the scientific method than to design, build and launch bottle rockets!

### Bottle Rocket Launcher

With a plastic soda bottle, a poster tube for a nose cone, and some cardboard, you can create your own rocket. Then just added a little water, compressed air and launch!

### Double Bottle Rocket Launcher

Launch two rockets at once! It’s great for racing your students’ rocket designs and you can also use it to test variables directly against each other.

### Air power projectile

Explore projectile motion with this 100% safe, chemical-free air-powered projectile. Flies straight and true with minimal wind effect and with a consistent, repeatable initial velocity – important for students testing predictions.

### Altitude Finder

Calculate altitudes, using triangulation, of objects such as our Air Powered Projectile and Bottle Rockets.

### Stop Watch Timer

New Digital Stopwatch and Timer captures elapsed time to within 1/100th of a second and lap time.

## Resonance Bowl: The Original Standing Wave Demo!

The Resonance Bowl can be traced back to ancient Tao tradition in China during the Han Dynasty (202 BC – AD 9) making this an ancient, but still highly effective, way to discuss and demonstrate behavior of waves and their interactions. Fill the bowl with water, rub the handles just the right way, and water will shoot up like tiny fountain jets. Some resonance bowl masters claim to even get water leaping as high as 2 feet!

The Concepts Behind the Resonance Bowl

The vibration of the handles, in turn, increases the vibrations of the bowl, causing the bowl to vibrate. In Physics, we call this Resonance, where one vibrational frequency causes the natural vibrational frequency of another object to increase. The vibration causes two phenomenons to occur:

a. The bowl will create a sound, depending on its size (~196 Hz for a “big” bowl and ~330Hz for a “medium-sized” bowl).

b. In addition, standing waves are created in the water illustrating an interference pattern called a Chladni pattern. Standing waves are produced by the addition of two identical waves traveling simultaneously in opposite directions through any elastic medium. These waves will constructively and destructively interfere with each other as they pass one another. The resulting composite wave from the addition of these two waves will form a standing wave in the metal rim. The standing wave that is produced sets up FOUR areas of maximum vibration called antinodes, these are areas in the water that “spout” and cause the water droplets to jump off the surface. There are also FOUR areas where minimum vibration occurs and these are known as nodes. These nodes show very little water rippling while the antinodes show maximum water rippling. With practice, you should be able to create four antinodes along the entire rim of the bowl that are so strong that the water will spray out of the bowl. This occurs where the artist intentionally engraved the four fish mouths.

Other Experiments

1. If the bowl is touched firmly at any of the antinodal positions, the finger will absorb the vibrational energy, and the waves will be reduced or totally stopped. This effect is called dampening. However, if the bowl rim is touched at any nodal area, there will be little energy lost since the node has minimal vibrational energy and the spouting should continue as before.

2. By varying the amount of water in the bowl, you can investigate with your student what might be the optimal water level for maximum effect and have them explain why. Is it easier or more difficult to create the standing waves with different water levels?

3. By rubbing harder and faster, you can cause the bowl to produce a high-pitched squeak. When it does, you can sometimes create additional nodal and antinodal points in the water.

4. Try floating a cork in the water while playing with the Resonance Bowl. Observe its movements.

5. You can also place a small amount of sand in the bottom of the bowl (…instead of water) and observe how the vibrations move the sand.

Thank you to Buzz Putnam of Whitesboro High School in Marcy, NY for his contributions to this article.

## Sound and Wave Products

### Resonance Bowl

See water dance to the vibrations from your hands with the Resonance Bowl. An ancient, but highly effective way to discuss and demonstrate the behavior of waves and their interactions.

### Spring Wave

No kinks in this wave! No more kinks in your wave experiments with this versatile but light, non-tangling plastic spring. Experiment with determining the speed of propagation of transverse and longitudinal waves.