п»їLaboratory VII: Rotational Dynamics

Difficulty #1: Instant of Inertia of a Intricate System

David Greavu

May 8, 2013

Physics 1301W, Professor: Evan Frodermann, TA: Mark Pepin


As soon as of masse of a complicated system was determined through two distinct approaches. A string was tied to and tightly wound around a horizontally disc and then strung on the vertical pulley where the opposite end was after that tied to a dangling weight. Below and fastened through the center of the dvd were a spool and shaft (all supported by a stationary stand). A ring was also dedicated to top of the dvd. The the whole length, spool, compact disk, and ring were free to rotate jointly. The chain was after that allowed to disentangle around the dvd, which as well allowed the hanging mass to come down. A video of the was used, uploaded, and plotted in MotionLab where it was used to construct horizontally position and horizontal velocity vs . time graphs. It absolutely was predicted which the moment of inertia in the system was equal to the sum of the individual moment of inertias (for each object in rotation). After studying the data as well as the subsequent graphs, the moment of inertia intended for the system was also determined as a function of the mass of the hanging weight, the radius in the disc, the law of gravity, and the velocity of the dangling weight. This kind of function was then in comparison to the original conjecture equation.


" Whilst examining the engine of your friend's electric snow blower you notice that the starter power cord wraps in regards to cylindrical band. This engagement ring is attached to the top of a heavy solid hard drive, " a flywheel, " and that disk is attached with a shaft. You happen to be intrigued by this configuration and decide to identify its instant of masse. Your good friend thinks you can add the moment of inertial by parts to have the moment of inertia in the system. To try this idea you decide to develop a laboratory style described under to determine the moment of inertia of a identical system from the acceleration from the hanging weight. ”

To be able to determine as soon as of inertia for a intricate system–such while the snowblower described above–this lab called for calculating the whole moment of inertia of a connected shaft, spool, compact disk, and band that rotated together as a result of a falling weight linked by a string tied to and wrapped about the disc and strung more than a vertical pulley. Moment of inertia is definitely the inertia–or is a tendency of an organization to retain similar velocity if perhaps not acted upon by external forces (Newton's First Rules of Motion)–of a rotating entity with respect to its rotation. The chain and the dropping, accelerating pounds modeled drawing the starter cord around the snow blower.


The tangential, linear velocity of the tight string mainly because it unwinds off of the disc was equal to the acceleration from the hanging fat as it descends (as is it doesn't same string). The system included each thing that was subject to rotation (the the whole length, spool, dvd, and ring). Since the mass and/or radius of each object could be immediately measured, in the beginning the system's moment of inertia was calculated simply by adding with each other each individual object's moment of inertia ( It was likewise possible to approach this matter using mechanics. The amount of the pushes in the y-direction (positive sumado a going downwards) acting on the hanging fat was identified to be [where Capital t is the stress of the line and g is velocity due to the law of gravity (9. 8 m/s2)]. Then simply, the rpm being placed on the compact disk is equal to (where ur is the distance from the axis of rotation that the power, F, can be applied). Considering that the pulley was placed tangent to the advantage of the disc (at a 90-degree angle), there is no need to work with cross-product formulations and the rpm is simply. Therefore ,

Thus, this approach called for deciding the speed of the dangling weight. This may be done through video analysis in MotionLab.


The string was tied to after which wound snugly around the dvd and strung over a pulley that was positioned...


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