Forest PHYS100 Chapt2
Chapt 2 Motion
Newton's Principia published in 1687 ( in latin and then 1726 in english).
Average speed
Average speed [math]\displaystyle{ (s) }[/math] is the ratio of the DISTANCE [math]\displaystyle{ (d) }[/math] you have traveled divided by the time [math]\displaystyle{ (t) }[/math] it took you to travel that distance.
- [math]\displaystyle{ \mbox{Average Speed} = \frac{\mbox{Distance traveled}}{\mbox{Time traveled}} }[/math]
We can write a formula to express the definition of speed using the above abreviations for speed, distance, and time
- [math]\displaystyle{ \bar s = \frac{d}{t} }[/math]
The bar over the [math]\displaystyle{ s }[/math] just used to indicate that it is an average.
An example of calculating your average speed
Suppose you drive from Pocatello to a friends house in Salt Lake. You know that the distance is 150 miles.
If it takes you 3 hours to drive there then your average speed is
- [math]\displaystyle{ \bar s = \frac{150 \mbox{miles}}{3 \mbox{hours}}= 50 \frac{ \mbox{miles}}{ \mbox{hours}} = 50 \mbox{ MPH} }[/math]
International System's (SI) unit for speed is
- [math]\displaystyle{ \frac{ \mbox{meters}}{ \mbox{sec}} =\frac{ \mbox{m}}{ \mbox{s}} }[/math]
Unit conversion
Converting the units from MPH to m/s is a matter of multiplying by 1.
Here are some useful value for 1
- [math]\displaystyle{ 1 = \frac{ 1 \mbox{m}}{ 621.4 \mbox{miles}}=\frac{ 1 \mbox{hour}}{ 60 \mbox{minutes}}=\frac{ 1 \mbox{minute}}{ 60 \mbox{seconds}}=\frac{ 1 \mbox{hours}}{ 3600 \mbox{seconds}} }[/math]
Instantaneous speed
Speed at a given instant in time.