[According to Ideal projectile motion states that there is no air resistance and no changein gravitational acceleration. This assumption simplifies the mathematics greatly, and is a close approximation of actual projectile motion in cases where the distances travelled are small.]1. [The positive x-direction is horizontal and to the right, and the y-direction is vertical and positive upward. The most important experimental fact about projectile motion in two dimensions is that the horizontal and vertical motions are completely independent of each other. This means that motion in one direction has no effect on motion in the other direction.]2[ A projectile is any object that has been thrown, shot, or launched, and ballistics is the study of projectile motion. Examples of projectiles range from a golf ball in flight, to a curve ball thrown by a baseball pitcher to a rocket fired into space. The flight paths of allprojectiles are affected by two factors: gravity and, on Earth at least, air resistance]3Base on this experiment ,we assume that the gravitation force is a positive value which is pointing downward. Beside, according to the collected data and the plotted graph it is obviously that the longer the Y (cm) the longer the X (cm) which the Y/X is linearly proportional to the X (cm). However, this experiment has some mistake due to human factor. For example, the ball may not place at the same spot each time during the experiment. During experiment, some precaution we should take to gain the actual result. For example we must make sure that the position of stand with wooden board isonly change in the height of it but never moved the angel between the table and the wooden block. During experiment, we make sure the position let the ball rolling down is always same.

- To investigate the trajectory of a small ball as it rolls off a surface which is
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