rotationaldynamics - 6 Rotational Dynamics Purpose: 1) To...

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6 Page 1 Purpose: 1) To study the rotational motion of solid discs on “air” bearings. 2) To investigate the residual frictional torque; the angular acceleration under a torque caused by a falling weight. 3) To study. the conservation of angular momentum when two rotating discs interact. Apparatus : The apparatus used for those experiments is well describe in the Instruction Manual and Expriment Guide for PASCO Model 9279 Rotational Dynamics Apparatus from which they were taken. A demonstration will be given at the beginning of the laboratory session in order to introduce the student to the system. Introduction: The PASCO Model 9270/9279 Rotational Dynamics Apparatus is a precision instrument designed to enable the student to make a quantitative study of rotational dynamics. The use of air bearings almost eliminates the effect of friction and, therefore, in many cases the student may perform an ideal or ‘textbook’ experiment. In order to obtain quantitative data the instrument is equipped with optical readers which permit digital measurement of angular velocity. Set-up: Familiarize yourself with the setup component in ±gure (1). A. Connection to the compressed air 1.Connect the apparatus to the source of compressed air via the 4.7 mm. I.D. clear plastic tube. The ²exible tube will ±t tightly over a rigid 6.4 mm smooth or barbed ±tting. The long ²exible plastic tube supplied with the apparatus supplies air for all the bearings used on the apparatus. 2. Caution: the air pressure entering the apparatus should not exceed 10 psi or be below 6 psi. For most experiments 6 psi is ideal. B. Leveling 1. The unit must be properly leveled otherwise any eccentric load on one of the discs will cause it to rotate with a non-uniform velocity/acceleration. 2. Place the unit on a steady, solid table. 3. Place the bubble level on the base plate and adjust the leveling screws until the unit is level in both the X and Y dimensions. 4. A more accurate leveling may be accomplished after the unit is set up. Turn on the air to the system (see the following section), place both top and bottom steel discs on the spindle and place a 50 gram weight on the edge Rotational Dynamics 6 6
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6 Page 2 Figure (1) Various components of the setup. PASCO scientific COUNTS UPDATED EVERY 2.0 SECONDS COUNT/SSEC 200 = REV/SEC COUNT/SSEC DISK SELECT UPPER LOWER 266 Disks (two steel, one aluminum) Digital display Base Optical readers Thumbscrews (one solid, one hollow) Drop pins Thread Level Thread holder Torque pulleys Air bearing pulley for hanging mass 25 g hanging mass Optical Reader Connections + 5 volts signal ground Leveling foot Optical reader output signals (yellow band marks output for top disk) 9 VDC Adapter Air inlet (for connecting compressed air supply)
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6 Page 3 of the top disc (to produce an eccentric load). Give the disc a very small velocity, less than 0.1 revolutions per second. Watch as the disc slows down. It should continue in the same direction until it stops. If the disc reverses
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rotationaldynamics - 6 Rotational Dynamics Purpose: 1) To...

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