Lab_#9

Anthony Putrino Lab Assignment 9: Gravity Instructor’s Overview As you continue with your study of physics, you'll learn that there are four fundamental interactions in nature. These interactions are summarized in this table: Interaction Comments Relative strength Effective range Strong nuclear force Binds protons and neutrons in nuclei 1 10 -15 m Electromagnetic force Force between charged particles. Follows inverse- square law. 10 -2 Infinite Weak force Responsible for certain types of radioactive decay 10 -13 10 -18 m Gravitational force Force between all objects. Determined by magnitude of masses and separation. Follows inverse-square law. 10 -38 Infinite So gravity is one of the four fundamental forces of nature. We will learn about the other three in Physics II . Some interesting things to note about the gravitational force:  In a relative sense, it is the weakest of the four fundamental interactions. Even so, gravity is largely responsible for the dynamics of our solar system, galaxy, and the Universe as a whole.  Gravity acts over an infinite distance. Objects may be separated by thousands of light years, but they experience gravitational attraction.  Gravitational interactions obey the inverse-square law.  Coulomb's Law dictating the force between two charged particles is also an inverse-square relationship. In this lab, you will perform experiments that illuminate the concept of gravitational interaction. This activity is based on Lab 10 of the eScience Lab kit. Our lab consists of two main components. These components are described in detail in the eScience manual. Here is a quick overview:  Experiment 1 : In the first part of the lab, you will subject a variety of objects to the force of gravity and discuss your observations.  Experiment 2 : In the second part of the lab, you will use a flashlight as an analogy to demonstrate the inverse-square law of gravity. JWH 1 Physics I

Take detailed notes as you perform the experiment and fill out the sections below. This document serves as your lab report. Please include detailed descriptions of your experimental methods and observations. Abstract This experiment focuses on the force of gravity and how it affects objects in particular. This force of nature will be observed in terms of how gravity pull’s an object to the center (the Earth’s core). Material and Methods Measuring tape, Styrofoam cup, scissors, flashlight, solid blocks, balls, ruler, writing utensil, marble, corks Results Based on your results from the experiments, please answer the following questions: Experiment 1: Falling in a Gravitational Field 1. The following expression for the acceleration due to gravity works well for objects near the Earth’s surface (G is the gravitational constant, M e is the mass of the Earth, and R e is the radius of the Earth): g = G M e R e 2 Use the above equation to calculate the gravitational acceleration at an altitude of 100,000 meters above the Earth. By what percentage is this acceleration different from that on the Earth's surface? = (6.67*10 -11 )(5.972*10 24 )/6,371, 000+100,000 = 9.52m/s 2 Actual gravitational acceleration on Earth’s surface = 9.81m/s 2 %Error = ((9.81m/s 2 - 9.52m/s 2 )/9.81m/s 2 ))*100 = 2.96% JWH 2 Physics I

NOTE : Be sure to specify your units. 1. How did the intensity (brightness) of the circle of light seem to changes as you increased the source distance? The intensity/brightness of the circle of light seemed to reduce as the source distance increased; inverse proportion relationship. 2. How did the area of the circle of light change as you moved farther away? How does this relate to the gravity field of a body? The area of the circle of light increases as it was moved farther away; the gravity field of a body similarly does the same thing. It also increases when a body is moved further away from another. 3. Make a plot of distance vs. area for the light shining from the cup to the wall (plot the area data on the y ‐ axis). 4. Draw a line of best fit through your data points, and comment on the general shape of your plot. What kind of relationship does this indicate (i.e. linear, exponential, logarithmic, etc.)? The plot is a straight line. This indicates a linear relationship between distance and area. 5. If the amount of light shining from the flashlight is constant, the intensity of light should decrease as the area it shines on gets larger. Using your plot from question 2, sketch an approximate plot for light intensity vs. distance. JWH 4 Physics I

6. If you moved too far away from the wall the circle of light probably became very difficult to see. Is the intensity of the light circle ever zero? Is it correct to say that gravity doesn’t exist between objects on opposite sides of the galaxy? If under these circumstances, then the intensity of the light circle could possibly be zero. It can be stated that gravity does not exist between objects on opposite sides of the galaxy because there is a lack of attraction. JWH 5 Physics I