Advanced Physics Through Inquiry 1 Teacher Guide

(PS-2848)

Teacher guide featuring 15 labs designed for Advanced Placement Physics 1.

Rotational Dynamics

Lab Summary

Students use a rotary motion sensor to determine the mathematical relationship between torque, rotational inertia, and angular acceleration of a rotating object.

Theory

How do net torque and rotational inertia affect the angular acceleration of a rotating object? Experimentally determine the mathematical relationship between net torque, rotational inertia, and angular acceleration of a rotating object.

Method

The Structured version of this lab activity is divided into two parts: Part 1 – Students use hanging masses to apply torque to a rotating arm, oriented horizontally (see figure below). In each Part 1 trial, students keep the rotational inertia of the arm constant and measure its angular acceleration while increasing the amount of applied torque by adding more hanging mass. A plot of angular acceleration versus net torque will show a straight line, and from that, students are expected to recognize the proportional relationship. Part 2 – Students use a fixed hanging mass to apply a constant non-zero net torque to the same rotating arm used in Part 1 while measuring the angular acceleration of the arm; however, in each Part 2 trial they keep the applied torque (amount of hanging mass) constant and vary the rotational inertia of the rotating arm by adjusting the position of two masses fixed to the rotating arm. Rotational inertia is increased as the masses are positioned farther from the axis of rotation. Students calculate the rotational inertia of the arm in each trial and then calculate the inverse rotational inertia (1/rotational inertia). A plot of angular acceleration versus the inverse of rotational inertia will show a straight line, and from that, students are expected to recognize the proportional relationship. Students are then expected to combine the relationships outlined in each part into one mathematical expression relating the three variables.

Sensors / Equipment Used:

PASPORT Rotary Motion Sensor

(PS-2120A)

Put a new spin on many common experiments with this highly versatile sensor.

Pendulum Accessory

(ME-8969)

This pendulum accessory converts a rotory motion sensor into a pendulum.

Super Pulley Kit

(ME-9433)

This combination kit includes the parts to build either a Super Pulley with rod or Super Pulley with clamp.

Mass and Hanger Set

(ME-8979)

Polycarbonate mass hangers with steel posts and "holed' masses that will not fall off. 4 hangers and 27 weights ranging from 1/2 g to 100 g.

Aluminum Table Clamp

(ME-8995)

This clamp with 6.5 cm grip width, accepts plain or threaded rods up to 1/2 inch or 1.25 cm.

Stainless Steel Rod, 60 cm Threaded

(ME-8977)

Threaded stainless steel rod with diameter of 1/2 inch.

Four Scale Meter Stick

(SE-8695)

A convenient measuring device that includes four different metric scales of various precision.

Black Thread (3 pack)

(ME-9875)

Black nylon thread.

Stainless Steel Calipers

(SF-8711)

These metric/English (18 cm/6 in.) calipers have an easy-to-read, expanded vernier scale of 20 divisions (instead of the usual 10) for increased precision.

Ohaus Scout SKX Balance 2000g

(SE-8757B)

Combines range, resolution and low cost, making it ideal for the student science lab. 2000 g version.

Materials Used:

The Ohaus Scout Pro Balance 2000g listed in the Materials and Equipment section is for classroom use, not individual lab stations.

Other Equipment:

Scissors

The Associated Bundle:

Advanced Physics 1 Expansion Bundle

(PS-2833)

Equipment and sensor expansion bundle for performing 7 experiments in the Advanced Physics through Inquiry 1 Teacher Guide.

Interface Required

This experiment may require software and an interface for data collection.