Lab Handout Lab 1. Projectile Motion: Which variable affects the hang time of a projectile the most? Introduction Projectile motion is defined as the flight of an object near the earth’s surface under the action of gravity alone. We have all see projectile motion at one point in time. Over 500,000 years ago, the first known humans attached stones to sticks to create spears for hunting. The laws of projectile motion govern the path that a spear follows once it is thrown so understanding the factors that affect projectile lead to creation of better spears and more successful hunts. Understanding the factors that govern projectile motion also enabled people to build new tools for launching projectiles that could travel further in the air and hit targets with great accuracy, such as bows and arrows, the trebuchet, and cannons. Today, people who understand the factors that influence projectile motion, as professional athletes such as basketball and soccer players do, earn the respect of many fans and can earn large salaries. In science, the modeling of projectile motion was of large importance and two great thinkers published works related to the topic. Aristotle’s view was that an object in flight followed a straight line until it “lost its impetus” and abruptly fell to the ground. Over 1600 years later, Galileo took up the task of studying projectile motion once more and published his results in the Dialogues of the Two New Sciences in 1638. When a projectile is in flight, we assume that gravity is the sole force acting upon it. The path of a projectile is a curve called a parabola, as shown in Figure 1. The object in flight will have horizontal and vertical components to its velocity at any given time. While scientists recognize that air resistance does affect the flight of a projectile, under most circumstances the effect of air resistance can be ignored. When we ignore air resistance, the horizontal component of velocity is governed by the horizontal component of the initial velocity and the vertical component of velocity is governed by the acceleration due to gravity. Figure 1. Projectile Parabola People often want to be able to predict where a projectile will land after its launched. For example, hunters, athletes, and engineers can all benefit from understanding how different variables affect projectile motion. There are a number of variables that may, or may not, affect the motion of projectile. These variables include the launch angle (denoted as 𝜃), the initial velocity of the projectile, the height of the initial launch, and the mass of the projectile. Some of these variables may also interact with each other so the effect of any one variable may differ depending on the value of another variable. People therefore need to not only understand how these variables affect the motion of a projectile but also how they interact with each other in order to understand where a projectile will land after it is launched. Through experimentation, practice, and careful study, you can gain insight into the affects of these parameters on objects in flight. 1 The Inquiry Task Use what you to know about projectile motion to design and carry out a series of experiments to determine which variable has the biggest impact on the hang time of a projectile. The guiding question of this investigation is, Which variable affects the horizontal displacement of a projectile the most? Materials You will use the projectile motion simulator found at: http://www.physicsclassroom.com/PhysicsInteractives/Vectors-and-Projectiles/Projectile-Simulator Step 1: Designing and Carrying out an Investigation In order to answer the guiding question, you will need to design and carry out several different experiments. Each experiment should look at one potential variable that may or may not affect the hang time of a projectile. Some potential variables include the initial angle, initial velocity, the height of the initial launch, and the mass of the object. To accomplish this task, you must determine what type of data you will need to collect, how you will collect it, and how will you analyze it before you begin. To determine what type of data you need to collect think about the following questions: ▪ ▪ ▪ What is required to measure each parameter? What is the independent variable? What will you hold constant? To determine how you will collect your data, think about the following questions: ▪ ▪ ▪ ▪ What will be your method for measuring the hang time of the projectile? How will you make sure that your data is of high quality (i.e., how will you reduce error)? How will you keep track of the data you collect? How will you organize your data? In order to determine how you will analyze your data think about the following questions: ▪ ▪ What type of calculations will you need to make? What type of table or graph could you create to help make sense of your data? 2 Step 2: Initial Argument Once you have finished collecting and analyzing your data, you will need to develop an initial argument. Your initial argument needs to include a claim, evidence to support your claim, and a justification of the evidence. The claim is your answer to the guiding question. The evidence is an analysis and interpretation of your data. Finally, the justification of the evidence is why you thinks the evidence matters. The justification of the evidence is important because scientists can use different kinds of evidence to support their claims. You will create your initial argument on a CER template. Step 3: Argumentation Critique by Instructor Figure 2. Argument Presentation on a Whiteboard Your instructor will review your initial argument and provide feedback to you. You will have a chance to revise your initial argument. You might need to gather more data or design a way to test one or more alternative claims as part of this process. Remember, your goal at this stage of the investigation is to develop the best argument possible. Step 4: ADI Report Once you have completed your research, you will need to prepare an investigation report that consists of three sections. Each section should provide an answer for the following questions: 1. What question were you trying to answer and why? 2. What did you do during your investigation and why did you conduct your investigation in this way? 3. What is your argument? Your report should answer these questions in 2 pages or less. This report must be typed and any diagrams, figures, or tables should be embedded into the document. Be sure to write in a persuasive style; you are trying to convince others that your claim is acceptable or valid! 3
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