lab4a10 - Physics E-1a Expt 4a: Conservation of Momentum...

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1 Physics E-1a Expt 4a: Conservation of Momentum and Fall 2010 The Ballistic Pendulum Introduction Preparation: Before coming to lab, read this lab handout and the suggested reading in Giambattista (through Chapter 7) and answer the questions in the Pre-Lab Questionnaire. Be sure to bring your completed Pre-Lab Questionnaire to lab along with this handout, writing paper, a calculator, and your copy of the Lab Companion . Post Lab Questions: At the beginning of each lab section, you will be given an additional handout with a series of questions to be answered and handed in at the end of the experiment. Try to answer these questions with one or two concise sentences. To answer the post lab questions satisfactorily you should pay special attention to all text that appears in italics in this handout. Background: The conservation of momentum principle may be applied to find the speed of a projectile by simple, direct measurement. The apparatus (still used in modern ordinance laboratories) was invented by Benjamin Robins in 1742 and bears the descriptive name Ballistic Pendulum. In its simplest form, the ballistic pendulum is a block of wood, hanging freely on ropes or wires and initially at rest. When a projectile is shot into the wood, the block begins to swing in a pendulum-like motion. The height to which the block (plus embedded projectile) rises is a measure of the speed achieved during the collision and that, in turn, is a measure of the speed of the projectile just before the collision. Overview and Objective : You will fire a paintball into a pendulum bob and measure how far it moves horizontally. Knowing that the pendulum swings in a circular arc allows you to calculate to what height it rose. From the maximum height to which it rose, you can then deduce the velocity it had at the bottom of the swing (using conservation of mechanical energy). The velocity at the bottom of the swing is the velocity after the collision of the paintball with the pendulum bob. Next you invoke conservation of momentum to figure out the velocity of the paintball before the collision — and that’s the objective. You will also measure the velocity of the paintball independently (using a dual photogate timer) to compare your mechanical measurements with the electronic measurements. This comparison will give you further ammunition in deciding whether or not the conservation laws were justifiably and correctly applied in this experiment.
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2 Experimental Setup: The apparatus shown in the figure consists of a pendulum bob (labeled canister) and a paintball marker mounted inside a wooden box. The pendulum bob is suspended from the ceiling. A paintball is propelled from a paintball marker by high pressure CO 2 gas. Theory The total linear momentum, !
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This note was uploaded on 10/26/2011 for the course PHYSICS E-1a taught by Professor Wolfgangrueckner during the Fall '11 term at Harvard.

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lab4a10 - Physics E-1a Expt 4a: Conservation of Momentum...

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