Lab_Measurements - Lab Purpose Measurement and Analysis...

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Lab Measurement and Analysis Purpose : This lab demonstrates difference methods of measurement and analysis. We will attempt to measure the constant acceleration of freely falling objects. Background : In the first part of the lab, we collect data using a meter stick and a stop watch. We use Excel to help us make sense of the data. First we use Excel to graph the data; we then use the fitting tool in Excel to interpret data mathematically. In another words, we use Excel to see how data sets correlate mathematically. In the second part of the lab, we will learn how to collect data using electronic sensor. Data collected by the motion sensor will be fed to the computer through the interface box. These data can be displayed and analyzed using the DataStudio software. Equipments: Meter stick, stop watch, 20 g mass, Excel, table clamp, 3 ft and 1 ft bars, cross Part 1: Stop Watch Measurement 1. We will use a meter stick and a stop watch to measure the initial heights and the times required for an object to fall through those heights. From this information we will calculate the acceleration. Use a small mass, say 20 g or 50 g (heavy enough to minimize air resistance but not too heavy just to be safe.) The initial heights are set to predetermined values; see the table below. For each initial height, measure the time it takes the object to hit the floor from rest 10 times. The same person should drop and time to reduce reaction lag. 2. Set up an Excel table like the one shown below and fill in the times. Always have your raw data available, preferably organized as well. H(m) T1(s) T2(s) T3(s) T4(s) T5(s) T6(s) T7(s) T8(s) T9(s) T10(s) Tavg(s) 0.5 0.75 1.0 1.25 1.50 1.75 2.00 3. Under the “tavg” cells, type in “=AVERAGE(B2:K2)” where “B2:K2” is the range of the cells where the times reside. You cell locations may vary. Hit the “enter” key when you are done. Check that the value under “tavg” is the average of the 10 individual times. Repeat for the other heights or use the “fill down” command. Analysis: Fit using quadratic fit See appendix I “How to Excel Plot and Fit” for instructions on how to plot this data and fit a parabola (quadratic fit) through this data. We now compare these coefficients to the model of what we think occurs. Kinematics tells us that the initial height relates to the elapsed time by the following equation. yf = yi + vi*t + 1/2*a* t 2 or yi = yf – vi*t – ½ *a * t 2 Note that yf represents the final height, its value should be zero, yi represents the initial height, vi represents the initial velocity, its value should be zero, and a represents the acceleration of the object, its value should be the acceleration of gravity or -9.81 m/s 2 .
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This is why we are using a parabolic fit since the initial height is a quadratic function of the elapsed time. Below, y is the initial height and x is the elapsed time.
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This note was uploaded on 02/09/2011 for the course PHYS 4A taught by Professor Nancy during the Spring '04 term at Foothill College.

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Lab_Measurements - Lab Purpose Measurement and Analysis...

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