Overview of Setup

1
Overview of Setup
R
Point Mass
Platform
r
Ffriction
T
Rpg
Hanging mass
a
a
mg
Purpose today is to measure the rotational
inertia for a point mass! I would use 100 to 200
grams for a hanging mass to keep the frictional
effects small!
2
Overview of Setup (Zoomed Top View)
Photogate
String
a
r
Rpg
a
3
Angular Acceleration Calculation

• All angular acceleration measurements are based
  off of the DvT /Dt measurement from the photogate
• Therefore, you need to know how the photogate
  triggers
• It calculates v in the following way
• Computer gives you Dt, you need to input Dx (Dx
  1 hole 1 solid region)
• Dx is inputted in the Data-gtUser Parameters
  menu in LoggerPro!
• A plot and fit to vT vs. time will give you aT (_at_
  Rpg) and thus a

4
Rotational Inertia

• Remember I St/a therefore if you measure the
  net torque and angular acceleration you find the
  rotational inertia!
• If St rT rm(g-a) then I
  rm(g-a)/a
• a is the tangential acceleration based off of the
  photogates measurement of a
• You will need to make two runs, thus two a
  measurements
• One to measure I0 of the apparatus alone
• One to measure I0 Ipoint mass
• Therefore (I0 Ipoint mass) I0 Ipoint mass
• Measure the point mass, mass (M) and its location
  on the platform (and calculate the theoretical
  value of Ipoint mass)
• Report should include velocity vs. time plots as
  well as aT and a calculations
• Please include an experimental percent error
  calculation based off your measured value of
  Ipoint mass and the calculated value
• Include some discussion of possible sources of
  error that may effect your results
• Report (worth 30 points) is due next week at the
  beginning of Lab!