# Centripetal Force and Rotational Inertia

Item no.: F11

##### Introduction

As our daily appliance, the rotational device could be found everywhere at anytime. Just like the rolling wheels in car’s motion, gyroscope in the steamer, even the spinning skill in the athletic game, hurricane arisen from air of large vortex and the existence of spiral galaxy in universal space, they all are assessed from the dynamical characteristic of body rotation. In this subject, the experimental kit is designed to experience the characteristic of force responsible for rigid body in circular motion, and rotational inertia for rotating object induced by torque.

##### Objective
1. Centripetal force induced by various mass in different radius.
2. Angular acceleration and moments of inertia of different bodies.
3. Steiner’s theorem (parallel-axis theorem).
##### Experiment— Centripetal force

A body of mass M moves on a circular path, variable angular velocity might be produced by adjustable radius and rotating rate. The required centripetal force for the body, in terms of relative parameters, will be developed below.

##### Experiment—Moment of rotational inertia

Base on the Newton’s second law F=ma and rotation motion for T=Iα , systematic moment of inertia could be summarized by individual moment of inertia, which depends on the separated mass and their distance to the rotating axis.

Generalized from these experiments, a disk, mounted as the vertical shaft, is subjected to an external torque induced by a mass connected to a stretched string around pulley. Based on r the value of hanged mass m, radius of disk R and angular acceleration, the rotational inertia of disk can be determined.

1. 向心力實驗
2. 轉動慣量實驗
##### 實驗器材：
1. 鋁製實驗平台 x1
2. 桌邊定滑輪 x1
3. 兩用轉動器 x1（直徑 6/8/10 )
4. 鋁製轉動器固定架 x1
5. 鋁製計時器固定架 x1
6. U型金屬砝碼架 x1
7. 鋼製砝碼 20g x5
8. 細魚線0.4mm x 100cm x 1
9. 轉動慣量用固定長軌 x1
10. 轉動剛體附孔可固定於固定長軌上：獨立質心重約250g x 2、圓棒直徑3cm/長20cm/重約1000g x1、圓環外徑20cm/內徑18.5cm/重約1000g x1、圓盤直徑20cm/重約1000g x1
11. 剛體固定用長螺絲 x2
12. 向心力實驗吊架 x1
13. 向心力指標器 x1
14. 直流馬達驅動器 x1
15. 向心力實驗用重物 x3，鋼鐵製含三鉤，重量各約160 / 115 / 78g