# Lab 9 Rotational Motion Formal Lab Report - Sharon Zhao...

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Sharon Zhao Partner: Sarah Brewington TA: Keither Thrasher Physics 107L-01 6/27/15 Rotational Motion Introduction Circular motion is the movement of an object along the circumference of a circle or rotation along a circular path. In this lab, rotational motion was explored by using a rotational motion apparatus to examine angular momentum, angular acceleration from a torque, and moment of inertia. With experimenting with rotational motion, we consider only rigid bodies. A rigid body is an object that retains its overall shape, and in this lab disks were used. The rotational motion of a rigid body occurs when every point in the body moves in a circular path along an axis of rotation. The angular displacement ( ΔΘ ) is the angle the object turns and is in units of radians. There are 360°, or 2 radians π in a circle. A radian can be found by dividing the arc length by the radius. Angular velocity is the change in angular displacement over time, defined by: ΔΘ / Δ t. Angular acceleration is the rate of change of angular velocity, α = Δω / Δ t. Angular and linear quantities can be related through 3 equations which are s=r Θ , v=r ω , and a=r α . In previous labs, we have explored kinematic equations for bodies moving at constant acceleration. There are very clear rotational counterparts for linear displacement, velocity and acceleration, so we are able to define an analogous set of equations for rotational kinematics. These include ω f = ω 0 + α t and Θ f = Θ 0 + ω 0 t + ½ α t 2 . Torque is a measure of rotational force and defined as force times the lever arm, Τ = FL. The level arm is the perpendicular distance between the “line of action” and the axis of rotation. If the definition of torque along with relationships between linear acceleration and tangential angular acceleration are substituted into Newton’s second law, we get Τ = I α . I, or mr 2 , is the moment of inertia of a point mass about the center of rotation for a disk/cylinder. Angular momentum is rotational momentum that is conserved and is a product of the moment of inertia and angular
velocity: L = I ω . The relevance to this lab is to explore these relationships between angular velocity, angular acceleration, torsion, and inertia through various disks spinning in a rotational motion apparatus. Procedure This lab was broken down into 3 experiments to explore different aspects of rotational motion. The first explored angular momentum through the inelastic sticking of two rotators. The masses and radius of two steel disks and one aluminum disk was found using a weight scale and ruler. The steel disk with the large center hole was placed at the bottom and the other steel disk was placed on top. We then opened the file “rot_motion” on DataStudio. After turning on the air pump and
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