### The Straight Story on Air-Powered Projectile Motion

WARNING! Goggles should be worn and care taken in the launching of the Air-Powered Projectile as it launches at a high velocity! Do not lean over the launch pad when pumping the air-pump.

With help from Joe Spaccavento, Science Supervisor/Physics Teacher of North Arlington High School in New Jersey and Section Rep, of NJAAPT, we would like to give you some real ideas for experiments and activities with the Air-Powered Projectile (APP).

Unlike solid-fuel rockets and water rockets, which have too many variables for accurately studying Newton's Laws, this safe, chemical-free air-powered projectile is ideally suited for exploring projectile motion.

The Air-Powered Projectile is technically not a rocket. It uses compressed air as "fuel" to power its launch. One of four thrust washers (sizes Low, Medium, High, and Super) is pressed onto the top of the launcher and the projectile slides down the launching tube. Air is pumped into the launcher with the air pump. When it reaches the pressure needed to launch the projectile, the thrust washer is forced off the launching tube, sending the projectile into the air.

An example used in many classrooms is to have students launch the projectile vertically and time how long it takes for the projectile to complete the trip up and down. This time is then divided in half to get a pretty good approximation for the time of the upward portion of the trip. You can then calculate the initial velocity of the projectile. Then calculate how far the APP will go when launched at an angle, using vectors. You can even place a target on the field where you have calculated and try to hit it.

### Collisions and Energy

Saw this at the last regional AAPT meeting. From grade school through college, you talk about energy transformations. Where does the energy go in a collision? There is no such thing as a perfectly elastic collision, so some of the energy always gets transformed. Take a Newtonian Demonstrator (Newton's cradle). Place a piece of paper between the first and second ball. Pull the first ball up as high as you can and let go. After the collision, pull the paper out. You will see a hole that has been burned through the paper. Where does the energy go as the balls slow down? One place is heat. If you have a very small version of the device, you may not see much of a hole. If you can get some, it works really well holding a piece of paper between two large (2 inch diameter or greater) ball bearings or stainless steel balls and banging them together with your hands.

### Laser Pointer Games

Laser pointers can be used to show many properties of light. You can show reflection and refraction with lenses and mirrors. You can show how color is absorbed. We believe that they can and should be used in the science classroom for light demonstrations. Yes, you do need to be careful with them. Don’t shine them in anyone’s eyes. Make sure that the principal knows what you are doing. Here are some fun activities to teach about light:

Do not try to tag others with the laser due to the potential of eye damage. Make a target. It can be virtually anything, as long as it will reflect the red laser light. Put it or hang it somewhere in the room.

Place the laser pointer on a steady object and use a clothespin or clip to keep the pointer on. Place a mirror on a desk and have the students move the mirror so that the laser light falls onto the target. (Putting on the desk keeps it steadier than holding it.) Move the target, the laser, or the mirror and try again. Have the students draw the relationship between the three objects. Add another mirror. Use chalk dust to show the beam as it reflects off the mirror and show that the incident angle and the reflected angle are equal.

For advanced students or physics students, you can place the laser and the target first and have the students calculate where to put the mirrors and at what angle before they try it. You can also have them hit the target without using mirrors or lenses (think windows, water, internal reflection, the floor, etc.)

To make this easier, try our new Adjustable Laser Stand. It holds a standard pen-style laser pointer. It adjusts to almost any angle and will hold the button on. It even comes with a Velcro® strap to attach it to a steady object like a ring stand.

### How does Wile E. Coyote violate the laws of physics and spacetime itself?

When I was teaching, this was my favorite quiz of the year. This would happen after we covered the force and motion chapters. Warner Brothers does not seem to keep any particular video selling for long. I used "Crash Course" which can be found on eBay still. There are some new tapes out there such as "Scrapes of Wrath" at Amazon.com or your local discount merchant. I haven't seen that one, but I would think it would work. The basic premise is that the students have to identify and explain impossibilities.

Click here for Wile E. Coyote cartoons

Some general rules: the Road Runner is infinitely strong and fast and also has infinite acceleration. Since this is science class, we are looking for science problems, not reality problems. In other words, trucks can appear out of pictures, but the Coyote cannot hover. Each episode is different, but some examples are: Classic Not Falling (CNF), not enough energy to go higher than started, cannot catch a falling object by falling, no external forces, no normal forces, etc. Depending on the level that you are teaching, the explanations can be simple or more complete. Physics students should be able to tell how and why a specific law is being violated. The students have fun taking a quiz!

### West Point Bridge Designer Contest

For several years, the United States Military Academy (West Point) has made a program available for free. You can construct a bridge, test the bridge, and calculate its cost. It also shows which members have the most stress, and that the members break when they reach their limits. It is fun as a stand-alone program. I used it in previous years for students to come in before or after school to test designs before they built their bridge for our bridge contest. The winners went on to IIT's regional contest.

### Weighing Air

Did you know that you can find the mass of air? Using a Pressure Pumper, you can pump up a two-liter bottle and find the mass of the air that you have added. This is a concept that is difficult for students to grasp – that air is matter and has mass. Click below to view the full activity.