Water Rocket Lab
Kinematics: Motion in Two Dimensions
AP Physics 1-212
Changzhou Senior High School of Jiangsu Province
This paper introduces an experiment about launching a water rocket. The projectile motion of this water rocket will be examined.In this experiment,the water rocket will be launched at 4 different angles 30°，45°60°and 90 °.We will measure the ranges,maximum altitudes and air time in order to have a better understanding of the projectile motion.As the practical situation which includes the air resistance and different kinds of errors caused by students’ carelessness is different from the theory,it is unaviodable that the results are quite different from the theoretic statistics. The horizontal velocity is related to the range, while the vertical velocity is related to the maximum altitude. This experiment can help us reinforce the concepts related to the motion in two dimensions although the water rocket does not have the ideal situation. A lot of equations we learned in class can help our group calculate the range and maximum altitude. Introduction
The purpose of the experiment was to reinforce the concepts related to motion in two dimensions using water rocket launches and the calculations necessary to determine launch speed and range.
(1) Because the water rockets are essentially pressurized chambers, they have the same launch speed, regardless of launch angle. (2) Ignoring air drag, a projectile will take the same time for its horizontal motion and its vertical motion. (2) Neglecting air drag, the horizontal velocity of a projectile will remain constant. (3) The vertical motion will have constant acceleration, g.
Equations: sy = voyt + ½ g t2 [ vertical motion]
R = voxt [horizontal motion]
The water rocket which is launched at different angles will fly into different heights in the sky and each time it will have different ranges when it drops. Method
The materials which are prepared to be used for this experiment are a timer, a water rocket, a meter ruler, a launch pad.
Firstly,we need to set the rocket on the ground so that the barrel is exactly vertical. Then we can fire it vertically two or three times, using stopwatches to clock total air time,determining average air time for the vertical launch.Secondly,we are supposed to use the vertical motion equation to find the launch velocity, vL, which, in this case only, is equal to voy.Thirdly,we need to calculate the horizontal and vertical components of the launch velocity for each of the 30, 45, and 60 launches, and make a component vector diagram for each of the launch angles like the following diagram. Example:
VL = 30 m/s Vy = 30sin 20 m/s
20 Vx = 30cos 20 m/s As a result,we can calculate the range, R, for launch at each angle.If you are willing to set a flag on the field at that distance from the rocket,you can do it.Finally,remember to measure the launch angle and secure the rocket barrel to fire at each of the angles just once, setting a flag where the rocket lands each time and measuring only the difference in range between the two flags to use in calculating percent error. Also remember to measure and record the "air time" for each launch. (不知道要不要分段，你看着办吧)图也不知道要不要 Results
Important results in verbal form
All of the useful lunch angles are 30 degree, 60 degree and 45 degree. The percentage errors of the data of angle 45is the smallest----0.3%. Therefore, our group will mainly use the data of this angle. Calculated Range at 45 degree is 32.6m. Vertical Displacement at 45 degree is calculated to be 15.5 m. The measured...
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