Advanced Physics Through Inquiry 1 Teacher Guide

(PS-2848)

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

Atwood's Machine

Lab Summary

Students use a photogate and pulley system to determine the mathematical relationship between the acceleration of an Atwood’s machine, the difference between its two masses, and the sum of those two masses.

Theory

How is the acceleration of the two masses of an Atwood’s machine affected by their difference in mass and by their total mass? Experimentally determine the mathematical relationship between the acceleration of an Atwood’s machine, the difference between its two masses, and the sum of those two masses.

Method

The Structured version of this lab activity is divided into two parts: Part 1 – Students transfer masses from the heavier side of the Atwood’s machine to the lighter side to vary the mass difference m2 – m1 (and thus net force) while keeping the total mass m2 + m1 constant. In each trial they determine the acceleration from the slope of a plot of the speed versus time while the masses were moving freely. Plotting acceleration versus the mass difference for all Part 1 trials will result in a straight line, and from that students are expected to determine the proportional relationship. Part 2 – Students remove equal masses from both sides of the Atwood’s machine to vary the total mass m2 + m1 while keeping the mass difference m2 − m1 (and thus net force) constant and determine the resulting acceleration as in Part 1. Plotting acceleration versus the inverse total mass (1/total mass) will result in a straight line, and from that students are expected to determine the inverse proportional relationship. Students are then asked to combine the two discovered proportionalities into an equation relating the three variables, and to determine the value of the proportionality constant k, which should be found to be near the value of the free fall acceleration due to gravity g. Finally, students are asked to derive the equation for the theoretical acceleration of an Atwood’s machine and compare it to their experimentally-derived expression.

Sensors / Equipment Used:

Smart Gate

(PS-2180)

Photogate that can be connected to any PASPORT interface, has auxiliary port to daisy chain gates, double beams for accurate speed measurement, and a special photogate tape slot.

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.

Right Angle Clamp

(SE-9444)

This clamp fits rods up to 18 mm (11/16 in) in diameter.

Black Thread (3 pack)

(ME-9875)

Black nylon thread.

The Associated Bundle:

Advanced Physics 1 Starter Bundle

(PS-2815)

Equipment and sensor starter bundle for performing 8 experiments in the Advanced Physics through Inquiry 1 Teacher Guide.

Interface Required

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