Kinematics: Motion in Two Dimensions

Cindy Cao

AP Physics 1-212

Changzhou Senior High School of Jiangsu Province

Abstract

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

Purpose:

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.

Background:

(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]

R=

t=

H=

A hypothesis:

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.