PHY101 Lab Activity 2 Forces General Advice Before starting any lab, it is recommended that you read the entire contents, think through the execution, and gather all materials and help you will need. Capturing photos of your work during this lab is easier with another person's help. Report All uploaded lab reports should contain the following sections: 1. Title - Your name, your ID, and the title of the experiment. If you partnered with other students, include the name and ID of the partner. 2. Introduction - A short intro or outline of the lab 1. Results - Your collected data and calculations. It is ok to write these by hand during the experiment, take a picture, and paste it in your document. 4. Conclusion - A short statement on what you did, what you learned, and how you think that reflects the goals of the lab. 5. Feedback - A short statement on lab difficulty and improvements. Your completed document should be 2-3 pages long. Objective In this activity you will confirm some of the properties of forces: their additivity, their vector nature, and the relation between the forces that a pair of objects exert on each other. Materials The following is a simple, non-exhaustive list of items that you will likely need. Phone/camera - to capture your experiment. Lab notebook/computer - to record data and observations. Ruler - to take smaller measurements. Measurements in this lab typically range from 2-15 cm. Rubber Bands - to "measure" force via deformation. Small "Hangers" - to hang objects from the rubber bands. Paper clips or hooks work well. Small Duplicate Objects - to exert a force on the rubber bands. Kitchen and household items such as coins, small cans, rice, beans, etc. work well. Ziploc Bags - to hold the objects. Pins or Nails - to affix the rubber bands to a board or wall. Board or Wall - for affixing the bands and placing the angle guide. Introduction Forces describe the interactions between objects. Your text provides examples of the different types of forces at both the fundamental level (eg, between particles) and the level of everyday interactions (tensions in ropes, gravity, bridges, etc.).

Forces are best described as vectors, mathematical objects with magnitude and direction. Newton's Third Law states that when an object A exerts a force on object B, then object B exerts an equal and opposite force on object A. In this experiment, we will observe some simple consequences of this idea. This experiment will help you identify some key properties of forces. We will deform a set of rubber bands by exerting a pulling force on them from two ends. The deformation will grow with the magnitude of the pulling force, proportional to the amount of force applied. Though rubber bands are a bit more complex, you will still observe this generic property: larger force produces larger deformation. Lab Procedure This lab has 6 parts - all are required for completion. Each uses rubber bands to understand the properties of forces. Each should be small and relatively easy to accomplish. Part 1. Calibrating forces Part 1 calibrates the force of individual and multiple objects on a rubber band. It provides a reference for the remainder of the parts. Increasing force should result in increasing deformation. Requirements A table of deformations against the number of hung objects. Pictures of your setup. Steps 1. Obtain three objects of equal mass. 2. Hang a rubber band from a fixed location on a board or wall. For hanging, you can insert a pin or nail or use your finger. You can also request a volunteer. 3. Measure the length of your rubber band at full extension but without stretching it. 4. Hang one of the masses from the rubber band. You may need to put the mass in a bag and use a clip to attach it. Ensure the object hangs freely with no other forces supporting it. 5. Measure the stretched length of the rubber band. 6. Repeat steps 5 and 6 with 2 objects and then 3 objects. We will refer to these as 0 (initial measurement with no stretch), 1, 2, and 3 units of force with deformation 0, 1, 2, and 3 respectively. Part 2. Force sensation Part 2 is qualitative. We will physically feel an increase in force by stretching different numbers of rubber bands to different lengths. The forces should feel stronger as the length increases. Requirements Simple statement of the feeling of increasing force. Pictures of your setup. Steps 1. Use two fingers from one or two hands to deform the rubber band to 1, 2, and 3 units of force. Part 3. Forces are additive Part 3 compared deformation from a single band vs 2 bands. The latter should result in deformation 1.

Requirements Simple statement of your observations. Pictures of your setup. Steps 1. Hang two rubber bands from a fixed location on a board or wall. 2. Hang two masses from both rubber bands at the same time. Make sure that the 2 bands equally contribute to holding the weight and are not tangled. 3. Measure the stretched length of the bands. Does that match the stretch of 1 unit of force? Part 4. Force sensation Part 4 is qualitative. We will physically feel the force of stretching one band to deformation 2 versus two bands to deformation 1. The force experience should be similar. Requirements Simple statement comparing the feeling of the forces. Pictures of your setup. Steps 1. Feel the force exerted by a single rubber band stretched to deformation 2. 2. Feel the force exerted by two rubber bands stretched to deformation 1. Part 5. Relations between forces Part 5 verifies that the forces between objects obey some simple rules . The total deformation of 2 bands should match deformation 2 from Part 1. Requirements Data recording the deformation of the bands. Pictures of your setup. Steps 1. Hang one band from a fixed location on a board or wall. 2. Hang another band from the first band. You might need to use a clip. 3. Measure the length of both bands at full extension (minus the clip), but without stretching them. 4. Hang 2 objects from the bottom band. 5. Measure the deformation of each band. Does the total deformation match deformation 2? Part 6. Forces are vectors. Part 6 verifies that forces are vectors by stretching 2 rubber bands at an angle. The deformation of each band 30o should be of 2 units. Requirements A simple statement describing your observations. Steps 1. Hold two bands freely in the air (see left image below). 2. Attach 2 masses to both bands at the bottom. 3. Separate the bands at the top so that they for an angle as shown on the right. 4. Spread the bands so that they make an angle of 30o with the horizontal (see right image below). It is helpful to print out the image in the Appendix use it as a background, aligning your rubber bands along the diagonal lines. 5. Affix the tops of the bands in place. It is helpful to use tacks or have a friend provide help. 6. Measure their extensions. Does the total deformation correspond to 2 units of force from Part 1? Notes and hints 1. Because we are using rubber bands, the deformations might not be uniform. Deformations 2 and 3 will likely be relatively larger than deformation 1. 2. If you are stuck, ask for help. Find internet resources, consult with classmates, call a friend, look for info in the discussion board or contact your instructor.