What is projectile motion?

, also called ballistic motion, is a form of motion in which an object or particle (called a projectile) is thrown near the earth's surface, and it moves along a curved path under the action of gravity only.

The only force of significance that acts on the object is gravity, which acts downward to cause a downward . There are no horizontal forces needed to maintain the horizontal motion – consistent with the concept of inertia.

Because projectile motion has many applications and is a simple example of two dimensional motion, subject to only one significant force, it is a common focus of introductory problems in physics courses. Theoretical predictions about projectile motion can also be easily checked using catapults, trebuchets, or small spring loaded canons in introductory lab activities, which are usually pretty fun.

Here is an example of a student built trebuchet which launched a rubber stopper over 12m in a classroom competition.

If a projectile is launched with an initial velocity ##v##, then ##v## can be written in unit vector notation as

##v = v_(x)hat i + v_(y)hat j##

The components ##v_x## and ##v_y## represent the amount of horizontal velocity and the amount of vertical velocity, respectively, and ##hat i## and ##hat j## are unit vectors, also in the horizontal and vertical directions, respectively. These velocity components can be found as follows if the launch angle ##theta## is known:

##v_x = vcos theta##, ##v_y = vsin theta##

If the projectile's range ##R##, launch angle ##theta##, and drop height ##h## are known, launch velocity can be found using Newton's formula

##v = sqrt((R^(2)g)/(Rsin2theta + 2hcos^2theta)##

The launch angle is usually expressed by the symbol ##theta##, but sometimes the symbol ##alpha## (Greek letter alpha) is used.

Reference link: http://en.wikipedia.org/wiki/Projectile_Motion