The Purpose of this Minilab • Gain experience in calculating and propagating errors associated with measurements. • Gain experience in performing rough estimations.
Finding Uncertainties from Repeated Measurements • Repeated measurements can give you different results due to • Object variation (e.g., the width of a table may be different at • different positions, or it may vary with temperature or moisture • in the air). • Measurement device or procedure may create scatter in the • result. Take many (5 or more) measurements and calculate the mean
Mean Standard Deviation A measure of how far individual data scatter. Standard Deviation of the Mean This is the uncertainty/error in the mean value. Result
Error Propagation A general physics formula….. And some measurement with uncertainties….. Plug in x, y, z….. to get value of “ f ” Calculate uncertainty in “ f “: Result
Estimations…an example How many (NT) new car tires are bought in Utah every year? P: Population: 2 Million A: % that are adults and drive a car: 60% M: Number of miles driven per adult per year: 15000 miles N: Number of tires per car: 4 L: Number of miles during life of tire: 45000 miles
What we will look at closely when grading… • Did you make reasonable estimations/calculations of uncertainties? • Did you report significant figures correctly? • Did you propagate your errors without mistakes? • When you performed an estimation, did you perform logical • reasoning to arrive at your estimate.