Video+Projectile+Lab

**Lab Title:** Video Projectile Lab **Authors:** Ali S, Branden M, Alex G  Goal: The goal of this lab was to develop an understanding of a moving, free falling object in order to create a "simulation of a car driving along a road and off a cliff."  Background: Projectiles are, by definition, objects that have only one force acting upon them. This definition, although correct, is very vague. What are the properties of a projectile? how does one act? Before beginning this lab, this and more was a mystery, as there are many myths surrounding the idea of a projectile. For example, Many believe that horizontal motion will keep a projectile in the air for a longer period of time. In this lab, this, and many other myths are dispelled.  Methods: We used the data we collected on the computer, as well as theoretical physics knowledge to come to our conclusions. Data:

[[image:science_graphs2.png]]
Analysis Questions: 1. Consider the __horizontal__ position (x) and velocity (vx) graphs. How would you describe the motion of the ball along the table? When in the air? The ball was moving at a constant velocity while on the table and while it was in the air.

2. Consider the __vertical__ position (y) and velocity (vy) graph. How would you describe the motion of the ball along the table? When in the air? While on the table, the ball did not move vertically. Once off the table, it increased speed and fell towards the ground.

3. Now consider the 2-D dot diagram (the movie window). Use a ruler to measure how far the ball moved horizontally for three dot intervals when on the table. In other words, measure horizontally dot-to-dot three times. If you chose to print a copy, you could record this information on the picture itself. Do the same to study the horizontal motion when in the air. Do these measurements support or refute how you answered (1) above? The calculations I got from measuring the distance between the three dots support our answer from question 1 because the distances do not change between intervals, meaning the ball is traveling at a constant velocity. Because the distances did not increase, the ball did not have to accelerate horizontally to cover that extra ground each second.

(4) Use a ruler to measure how far the ball moved vertically for three dot intervals when on the table—not so interesting, huh?! Do the same to study the vertical motion when in the air. Do these measurements support or refute how you answered (2) above? During free fall, the vertical distance of the ball increased at every interval. This supports our answer from question 2 because, if the vertical distance between each interval is increasing, the ball must be accelerating per second to cover that extra distance.

(5) What is the horizontal acceleration of the ball while in the air? Use your data to determine an answer. The horizontal acceleration is zero because the x velocity/time graph has no slope and because the distance between each interval is zero(see question 3).

(6) What is the vertical acceleration of the ball while object while in the air? Use your data to determine an answer. We used the class data and found the slope to be -10.38. This number is similar to the force of gravity which is -9.8.

(7) Explain what happens when a bullet is shot horizontally and another one is dropped from the same height at the same time. Why does this happen? Both bullets hit the ground at the same time because the only force acting upon the bullets is gravity. They are both dropped from the same height, so they hit the ground at the same time. ====Conclusion: The video game company has definitely come to the right place. After careful study of the lab results, our group has a complete understanding of the reality of the situation. At first, we thought that the horizontal speed of the ball will keep the ball in the air for longer. This is false. The y velocity/ time graph and our knowledge of the force of gravity was one of the biggest give aways. By taking the slope of the y velocity/vs time graph during the ball's free fall, we see that the acceleration was -10.38 m/s^2. -10.38 m/s^2 is incredibly close to the acceleration of any object due to gravity on earth. Because of this, we can infer that a ball dropped without an x velocity will accelerate down to earth at (approximately)-9.8m/s^2. This means that, even though the ball that rolled off the table had an x velocity, it did not effect the time the ball took to hit the ground. A ball dropped from the same height with no x velocity will drop at the same rate and hit the ground at the same exact time. Next we realized that the x velocity of the ball was constant, and falling off the table did not alter it at all. By viewing our x velocity/ time graph and our x position/time, we found that even after the ball rolled off the table it continued at a constant speed. The reason for this, just as the realization before it, has to do with forces on the ball. The ball is set in motion when a force is applied on it. That ball then rolls without an applied force. If the ball was something else, say a block on carpet for example, friction would also act upon it while it is on the table. In this situation, though, friction is negligible because the ball is rolling. As the ball rolls of the table, nothing has changed. There is still no friction, and no applied force, so with no forces pushing it or pushing against it, the ball simply continues at a constant pace until hitting the ground below. With these two realizations, we can conclude that the x velocity has no effect on the y velocity. Knowing this, we can construct a video game simulation that is as realistic as the ball experiment was in real life. ====