by: Tami O’Connor
One of the things I enjoy most about my job at Educational Innovations is conducting teacher workshops. It’s not quite the same as being in the classroom in front of twenty-plus students, but it’s fun nonetheless. My favorite presentation is titled, 3-2-1 Blastoff! In it, we deal with energy, forces, and motion. I use the Mighty Missile Launcher to demonstrate these topics.
It is exactly that… a missile launcher. The good news is this missile launcher can be used safely in a classroom with children from kindergarten to High School. Participants need safety glasses or goggles.
The launcher is primarily constructed of a film canister, a straw, and a balloon. The balloon has a sponge-like material inside that functions to re-inflate the balloon quickly. The balloon is attached to the film canister so little air is able to escape. The film canister pivots, allowing you to aim it at differing angles. The four missiles are simply straws, sealed on one end, with foam fins that stabilize them as they fly through the air.
I first demonstrate how the missile is launched. The missile is loaded onto the launcher by sliding it onto the straw that is slightly less narrow than the missile. Since the balloon is connected to the film canister, air can flow easily between the two. Depressing the balloon forces air into the film canister and out through the attached straw. When a missile is loaded onto the straw, the forced air propels it into the air. The harder and more quickly the balloon is squeezed, the faster the air flows into the missile.
Next, I make groups of three or four individuals, and I challenge my teachers to consistently land three out of four missiles inside a target area 1 meter away. Seems like a cinch, right? Not so fast… As with every good science activity, there are several variables that must be controlled. The first is the force at which the missile is launched. The harder and faster the balloon is squeezed, the faster the air is compressed and the farther the missile travels. The second is the angle at which the film canister points. The greater the angle, the higher and shorter (in horizontal distance) the missile travels.
So, the question is, how can we control these variables? In my workshop, I provide rulers and protractors. The participants quickly learn that controlling the force is not an easy task. Most people try to use their hands to launch the missiles, but it is difficult to apply the same force for each launch. That’s where the ruler comes into play. By finding an object that can be dropped onto the balloon at a constant height, participants are better able to control the amount of force applied to the balloon.
The protractor is used to control the angle that the turret is pointing. The angle must be smaller if the force is less and the angle must increase if the force increases. Participants also realize that after most launches the launcher moves. Using some masking tape to secure the launcher to the table can control this problem.
The missile launcher most easily teaches Newton’s Laws of Motion.
Newton’s first law states that an object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called, “the law of inertia”.
The missile will remain on the launcher until acted on by a force. The force that propels it is the unbalanced force of the air inside the missile pushing against the inside of the balloon. In deep space, where there is no air and little gravity, the missile, once launched, will continue on forever, unless it runs into another force (which could be an object traveling in another direction). Here on earth, the friction from the air molecules slows the missile, and gravity pulls it downward.
According to Newton’s second law, acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). This principle is also expressed using the equation F=ma
Newton’s second law, F=ma can be illustrated by the force with which you depress the balloon. Since the mass of the missile is constant, the greater the force at which you launch it, the greater the acceleration. The greater the acceleration, the farther the distance the missile travels. An interesting way to take this one step further is to add some mass to each missile. By keeping the force constant, students can see that more massive objects have less acceleration while using the same force.
Newton’s third law states that for every action force there is an equal and opposite reaction force.
As the air shoots out of the base of the missile a force is applied to the film canister and to the air behind the missile. As a result, an opposite force is applied to the missile. Since the missile has less mass than the launcher, the missile is propelled into the air.
This activity is a favorite of teachers and students alike. It looks easier than it is, and, by the end of the activity, participants gain skills working in teams and experience with force and motion.