Projectile motion can be one of the most entertaining topics for a science fair project. Designing devices that will propel objects is a challenging undertaking, and the results can be powerful -- and surprising. Science fair projects involving projectile motion tend to analyze one or more of the same factors.
One of the chief enemies of motion is friction. This can take on several forms: friction of a projectile fighting against the air (and against wind), of a projectile rolling along the ground or another surface and friction acting on a projectile while it is still inside the firing chamber or barrel. Projects seeking to predict a projectile device's effectiveness will need to analyze the role that friction plays. Inside the device, friction affects the device's effectiveness; outside the device, friction becomes a control factor when testing different devices.
One obvious constant for any experiment involving projectile motion is the force of gravity. It increases an object's velocity at 9.8 m/sec^2 while in the air affects fired projectiles. However, gravity also affects projectiles traveling inside firing barrels and rolling up and down hills.
Potential vs. Kinetic Energy
Potential energy refers to an object's ability to move, or use kinetic energy, in the right conditions. For example, if you roll a boulder up a hill, you're increasing that boulder's potential energy, because if you roll the boulder down a 10-foot hill, it won't travel nearly as far after the ground becomes level as it will if you roll the boulder down a 90-foot hill. The firing of a device lends more kinetic energy to the object, but the positioning of the device is one factor that will contribute to the amount of potential energy in the process.
Effect of Collisions
When two projectiles collide, or when a projectile hits an object, that projectile's flight is affected. The specific effect depends on the relative weights of the projectiles and the shape and weight of the object in question. Such outcomes as the coefficient of restitution -- an important metric in the design of baseballs -- are the result of many related experiments over time.
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