2LA_Lab_8_SecondLawRot3 - Physics 2LA The Second Law in...

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Physics 2LA The Second Law in Rotation (Includes Pre Lab Assignment) When a force causes an object to rotate, the angular acceleration α , depends on the force r F , the point at which the force is applied r , and the moment of inertia of the object I. r r r r rFI ×= α In this lab we will first confirm this relation by varying F and r and measuring α for an object with fixed I . Next we will use this relation to measure the moment of inertia for two simple objects. In both cases, a hanging mass will provide the force. Apparatus We will use the Pasco “ Introductory Rotational Apparatus” set up as shown in Figure 1 below. The apparatus with platter and its attached pulleys will have been leveled before you come into the lab. A plastic pulley, a string, and a set of masses (which includes a 5 gram hanger, a 5 gram mass, two 10 gram masses, a 20 gram mass and a 50 gram mass) will be used to provide the force. The string is tied to the bottom of the Rotational Apparatus platter and wound around one of three attached step pulleys. The plastic pulley is placed on a clamp at the edge of the apparatus so that the hanging mass can move freely. The smart pulley is in contact with the circumference of the platter. It will record the angular position, velocity, and acceleration of the platter through the computer. The Data Studio software is already calibrated for the Rotational Apparatus . In the second part of the experiment, a metal bar and a ring will be used to provide additional moment of inertia. A scale will be used to measure masses. A vernier caliper will be used to measure the diameter of the step pulleys. A ruler will be used to measure the bar and the ring dimensions. Main Platter Smart Pulley Table Clamp Pulley Hanging Weight Smart Pulley Rubber Band Tensioning screw Three Step Pulley Student Desk Figure 2 - Rotational Apparatus (side-view) Figure 1 - Rotational Apparatus (top-view) Hanging Weights Pulley Introductory Rotational Apparatus Three-step Pulley (Enlarged view) String fastening Screw Smart Pulley Cable to Computer
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The Physics In a simple rotational system, the torque and angular acceleration are related by the Second Law for rotating systems r τ = I r α where the torque is r = r r x r F . Since our force is coming from a hanging weight, we could write F = mg , and then I mgr = α (1) But this is only an approximation . From the figure below, we see that the hanging mass is accelerating as well, so
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This note was uploaded on 09/30/2009 for the course PHYSIC2LA phy taught by Professor Robertclare during the Spring '09 term at UC Riverside.

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2LA_Lab_8_SecondLawRot3 - Physics 2LA The Second Law in...

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