Approximations units and estimates PHYS116 A03 82809 Lecture

Approximations, units and estimates PHYS-116 A-03, 8/28/09, Lecture 2 Momchil Velkovsky

Approximation and simplification in physics Science: we can search only under the light posts. From time to time, technology provides a new light.

Approximation and simplification in physics Each physical theory (even the fundamental ones) has its limits. E. g. neglecting air resistance in Galileo’s experiments, idealization of mechanical objects. ¡

Approximation and simplification in physics N Fw Fs G

Baking a turkey You have read in a cookbook that you need 3 hours to bake a 10 lb turkey. Do you think that a physicist can estimate correctly the baking time of a 12. 5 lb turkey, without knowing anything else? 1. 2. Ye s No

Uncertainty and significant figures You have a steel ball bearing. You measure its diameter with a ruler to be 6. 5 mm. You find in a handbook that density of steel is 7856 kg/m 3. What is the mass of the ball bearing? 1. 2. 3. 1. 12964 g 1. 1 g 1 g

SI units and prefixes A homeopath tells you that each tablet of his medicine contains a yoctogram of gold. How many gold atoms are there in a tablet?

Dangers of subtraction You need to measure 100 ml of water for your bread maker. You have a 1 l pot and 90 ml cup. Your brilliant idea is to fill your pot and then fill the cup ten times from it. What remains will be 100 ml. Will it work? 1. 2. Yes No

Estimation How many molecules of water are there on the Earth? ¡ Could the shah pay to the inventor of the chess game? ¡

Reading for next time: Sections 2. 0 -2. 3 ¡ Go to ILT and answer the question at least an hour before Monday’s lecture. ¡ The homework for next Thursday will be published later today (on Mastering Physics). ¡ There is a introductory homework assignment due Monday noon. ¡