Lab Free Fall - Physics 1

Lab: Free Fall Objectives After you have completed this laboratory, you will be able to: Calculate the distance and displacement of a freely falling object, given the time of flight. Calculate the average velocity and instantaneous velocity of a freely falling object. Explain how mass affects the acceleration of a freely falling object. Differentiate between an object’s average speed and average velocity. Introduction Free fall describes the motion of an object that is falling downward, influenced only by the pull of the Earth’s gravitational field. In real experimentation, it is difficult to achieve a true free fall motion since air resistance is always present. Air resistance is a force that pushes an object opposite its direction of motion, and therefore the object will have a smaller acceleration than it would if air resistance were not present. The acceleration an object experiences near the surface of the Earth is a downward constant 9.8 meters per second squared (m/s2). Although it is possible to obtain this would have to have sophisticated timing equipment or a value by experimentation, you very tall height from which to drop the test object. Also, you would have to drastically reduce air resistance to get an accurate value of 9.8 m/s2. In this laboratory you will first experiment to determine which objects fall faster—heavy or light ones. Then you will throw a ball in the air and measure the time that it is in flight. Many other values can then be calculated describing the motion of the ball. Purpose of This Lab The purpose of this lab is to determine which falls faster, heavy or light objects. You’ll also describe and analyze the motion of a freely-falling ball. Questions 1. Suppose you drop a bowling ball and a golf ball out a second story window. Which ball would hit the ground first, and why do you think that? The bowling ball because it is heavier. 2. What is the difference between distance and displacement? Between speed and velocity? Distance is how far you go while displacement is the distance from the initial point and final point. Speed is how fast you are going while velocity is how fast you are going with direction. Hypothes Hypothesis is After reading the lab instructions but before starting the lab, record your best “educated guess” about what will happen in the experiment. Write the hypothesis as an “if-then” statement. Give your reasons and outline any assumptions that lead you to this hypothesis. If an object is heavier, then it will fall to the floor faster. Experiment: Free Fall In this laboratory you will first determine whether or not mass has an effect on how fast an object falls. You will also explore objects falling with and without air resistance. Then you will throw a ball in the air and analyze its motion using kinematic equations. Materials Ball, such as a tennis ball or small bouncy ball Stopwatch Outside area with a clear height to throw a ball upward Heavy book with a cover that is at least 8 ½ x 11 inches, such as a textbook. 1 sheet of 8 ½ x 11 inch paper Safet Safety y Precautions Be safe as you work on this or any lab. Follow these steps to safely conduct the experiment: When dropping the book, take care to drop it onto a flat surface, such as a carpeted or hardwood floor. Be careful not to drop the book onto your foot or anything else that could be harmed or broken by the impact. When throwing the ball outside, be sure to have a clear area overhead so you don’t hit anything above you. Getting Started Gather all materials from the materials list. Procedure Part 1: Heavy vs. light objects 1. Take the sheet of paper and hold it at chest level, flat to the ground. 2. Drop the paper and observe the motion of the paper as it falls to the floor. Record your observations in the Data section. 3. Take the heavy book and hold it at chest level, flat to the ground. 4. Predict: Will the heavy book fall faster or more slowly than the paper did? (Record your thoughts.) Drop the book and observe it fall to the ground. Were you correct? (Record.) 5. Why do you think the book hit the floor sooner than the paper did? (Record.) 6. Now take the paper and place it flat on top of the book. Raise the book and paper combination to chest level. What do you think will happen when you drop the book and the paper combination at the same time? (Record.) 7. Drop the book/paper combination. Record your observations. (Hint: Placing the paper on top of the book almost eliminates air resistance on the paper.) 8. Which fell faster now? Why? Part 2: Analyzing motion of a ball in free fall 1. Take the ball and stopwatch to an outside area where you have space to throw the ball high in the air with no obstructions. 2. Throw the ball slightly forward and watch its path. In the Analysis section, create a sketch of the path of the ball from the time you throw it upward until it returns to its starting height. Include an arrow that shows which direction you choose as the positive direction. 3. This time you will time the flight of the ball. This time throw the ball directly upward. Start the stopwatch when you release the ball and stop it when the ball reaches back to its initial height. 4. Record the time in the Analysis section of the report. Disposal aand nd Clean up 1. Return all materials to their proper locations and put away all other tools. 2. Recycle or reuse paper. Data Observations of paper falling to the ground: Predict: Will the heavy book fall faster or slower than the paper did? Faster Observations of book falling to the ground: Was your prediction correct? Yes Why do you think the book fell faster than the paper did? What do you think will happen when you drop the book and the paper combination at the same time? The paper will fall slowly because it is lighter while the textbook is heavier, pushing against the air resistance. Observations of the book/paper combination falling to the ground: Which object fell faster now? Why? The textbook because it is heavier. In the absence of air rresistance esistance esistance, explain whether heavy or light objects hit the ground sooner. They will reach the ground at the same time because the heavier an object is, the less air resistance there is pushing against the object but if there is no air resistance at all, the two objects would fall at the same rate and reach the ground at the same time. Anal Analysis ysis Draw a sketch of the ball’s path from leaving your hand until it returns to its starting height. Be sure to label “up” as “positive.” Total time of flight: Next, assuming negligible air resistance, show all work and calculate the following values. 2 Use g = -9.8 m/s (the negative indicates the downward direction). Time from throw to top of path ONLY. (Hint: It should take the ball the same amount of time to reach the top of its path as it does to return to the starting position.) 0.50 sec Instantaneous velocity with which you threw the ball. (Hint: Look at only the first half of the trip, and think about the value of the velocity at the top of the path.) Use this equation: vf = at + vi. 4.9 Instantaneous velocity of the ball when it returns to its starting height. (Hint: Pay attention to the direction!) Use this equation: vf = at + vi. -4.9 The maximum height achieved by the ball above its starting point. (Hint: Again look at only half of the trip.) Use the equation s = ½ at^2 + v t. 3.0625 m Displacement of the ball from starting point to ending point. (Hint: Think about the definition of displacement.) 0 Distance the ball traveled from starting point to ending point. (Hint: Think about the definition of distance.) 6.125 m Average velocity of the ball from starting point to ending point. (Hint: Think about the definition of average velocity.) Use the equation v = s/t. 0 Average speed of the ball from starting point to ending point. (Hint: Think about the definition of average speed.) Use the equation s = d/t. 12.25 sec Conclusion After conducting the experiment, how would you now explain the problem(s) or answer the question(s)? Were you able to support your hypothesis or not? Be sure to base your answer on the data you collected. Consider whether your conclusion is the only explanation for the data you collected or if there could be alternate explanations. Use these prompts to guide you in writing your conclusion. Summarize the results of the book and paper drop. In the absence of air resistance, which falls faster, heavy objects or light objects? Explain. How does air resistance affect the falling of objects? Why do many people think that heavy objects fall faster? The acceleration due to gravity in free fall always points downward. Explain in words the motion of a ball as it rises to the top of its path and falls back down. Use the words velocity and acceleration in your explanation. The hypothesis was supported by the experiment. The absence of air resistance will make all objects reach the ground at the same time and air resistance affects these objects by pushing against them while they’re falling but objects will negate the air resistance the heavier it is. The ball rises up and as it goes to its maximum height, the velocity becomes 0. The velocity goes up and acceleration goes up. Additional Que Questions stions 1. Suppose you dropped the heavy book and the paper at the same time from the same height, but this time you crumpled the paper into a ball to minimize air resistance on it. Which one would hit the ground first? Why? (Try it and see.) The book because it is heavier. 2. If you could throw the ball with twice the speed as in your trial, how would that affect the time of flight? The maximum height? The maximum height would not change, but it would take less time for it to return to its initial point. 3. If your experiment does not seem to match the expected results, what did you learn from the experience? If you were to repeat the lab so that the results were closer to what was expected, what would you do differently? I could have thrown the ball better.