Reading for Friday
Reading
o Chapter 2, sections 1 - 4
Reading Goals
o Define displacement, velocity, speed, and
acceleration.
o What is the difference between speed and velocity?
o What is the difference between speed and
acceleration?
o What is the difference between average and
instantaneous speed/velocity?
o How to calculate acceleration for an object whose
velocity is changing.
MasteringPhysics
 HW 1: Units (due 09/06)
 Velocity pre-lecture video (due 09/01)
Estimate the number of dentists in New York City.
Population of NYC ~ 10 million
How often does the average person see a dentist every year? ~ 1
 10 million patient visits/year
How much time do they spend with the dentist? ~ 30 minutes
A dentist sees ~100 patients per week or 5000 patients/year
10 million patient visits / 5000 patients/dentist
= 2000 dentists
Calculations with Significant figures
Significant figures are a measure of precision.
Adding and Subtracting
– Use the smallest number of decimal places.
Multiplying and Dividing
- Use the smallest number of significant figures.
Examples:
16,584 m + 8.3 m =
16,584 m × 8.3 m =
Express the sum of 248915 m + 13.97 m using the
proper number of significant figures.
Express the product of 248915 m + 13.97 m using
the proper number of significant figures.
Metric mishap caused loss of NASA orbiter
September 23, 1999
NASA lost the $125 million Mars Climate Orbiter because a
Lockheed Martin engineering team used English units of
measurement while NASA used the more conventional metric
system for a key spacecraft operation.
After a 286-day journey, the probe fired its engine to push itself
into orbit.
A piece of ground software supplied by Lockheed Martin
produced results in English units (pound•seconds), while a
second system, supplied by NASA, expected those results to be
in SI units (Newton•seconds). Due to the discrepancy, the
climate Orbiter likely either burned up the atmosphere or
continued out beyond Mars and is now orbiting the sun.
http://www.cnn.com/TECH/space/9909/30/mars.metric.02/
SI Units (the Metric System)
Base units:
Length – meter (m)
Mass – kilogram (kg)
Time – second (s)
MKS system: Most other units derived from these 3
Examples:
o velocity (m/s)
o acceleration (m/s2)
o force (N or kg·m/s2)
Table 1-4
Know
these
1 km = 1000 m
1 cm = 0.01 m
1 mm = 0.001 m
Unit Conversion
Express 8432 m in kilometers.
Conversion factor: 1000 m = 1 km
Unit Conversion
Express 8432 m in kilometers.
Conversion factor: 1000 m = 1 km
To convert 8432 m to km, multiply by the
conversion factor expressed as a fraction:
1 km
1=
1000 m
Unit Conversion
Express 8432 m in kilometers.
8432 m ×
1 km
1000 m
= 8.432 km
Unit Conversion
How fast is 60.0 miles per hour (mph) in meters
per second (m/s)?
Given
1 mile = 1.609 km
1 km = 1000 m
Unit Conversion
How fast is 60.0 miles per hour (mph) in meters
per second (m/s)?
Given
1 mile = 1.609 km
1 km = 1000 m
Answer: 26.8 m/s
Unit conversions are on the inside front cover of
your textbook.
For more help with units conversions:
http://www.youtube.com/watch?v=lAan6L9UjsE