WHAT IS NASA PHYSICS?
MODULES
Forces and Motion
Conservation of Momentum & Energy
Temperature and Heat
Fluids
Optics
Electromagnetic Spectrum
Modern Physics
Anticipation Guide 7
Intro to Modern Physics
Blackbody Radiation
The Ultraviolet Catastrophe
The Photoelectric Effect
Bohr's Atom
Spectra
Radioactive Decay
Special Relativity (SR)
Simultaneity
Distance and Time
General Relativity
May the Forces be with You
Modern Physics Notebook
Assessment Problems 7
Useful Things
SITE MAP
Forces and Motion
Anticipation Guide
Speed and Velocity
Acceleration
Gravity
Projectile Motion
Orbital Motion
Newton's Laws of Motion
Assessment Problems
Miles and Kilometers
Here is a scientific secret.
Scientists don’t think in miles, feet or inches. All scientists on Earth use metric units such as kilometers, centimeters and millimeters. The reason is that metric units are MUCH easier to convert from one to another because all are multiples of 10. For example, it is much easier to convert kilometers to meters (1 km = 1000 m) than miles to feet (1 mile = 5280 ft). To avoid these conversion woes, from now on in this book, all measurements will be in metric units. Here are some conversions. A complete list is in the Appendix.
Equals
1 mile
1 ft
1 in
1 km
1 m
1 cm
1 mm
1.61 km
0.30 m
2.54 cm
0.62 mi
3.28 ft
0.40 in
0.04 in
=
=
=
=
=
=
=
For more information, check out the following websites:
• Flight Path to Mars: How Long? Along what Path?
Speed and Velocity
Solve This!
Equation 1 works for any set of distances and times, even if you want to plan a trip to Mars, seen here in an image taken with the Hubble Space Telescope. To travel to Mars, NASA selects a trajectory that uses the least amount of rocket fuel (rocket fuel is expensive). To do this, we cannot travel in a straight line between Earth and Mars (because the gravity of Earth and Sun bends trajectories) but instead in an orbital path around the sun called a Hohmann Transfer Orbit. This takes approximately 8 1/2 months, and if done correctly the rocket and Mars arrive at the same location simultaneously.
Hohmann Transfer TrajectoryLaunch Animation
Answer: 64000
Here is how to do the problem:
v = d/t = 4.0 x 10^{8} miles/(260 days x 24 hrs/day)
v= 4.0 x 10^{8} miles/6.1 x 10^{3} hrs = 0.66 x 10^{5} m/h = 6.6 x 10^{4} m/h = 66,000 m/h
The only thing difficult here is converting 8.5 months to hours.
Using the metric units for the Mars problem:
Travel time = 260 days
Distance traveled: 640 million km
(converted from miles with 1 miles = 1.6 km)
v = d/t = 640,000,000 km/260 days = 2,500,000 km/day
v = 103,000 km/hr
Screamingly fast!
© 2013 by Wheeling Jesuit University/Center for Educational Technologies®. 316 Washington Ave., Wheeling, WV 26003-6243. All rights reserved. Privacy Policy and Terms of Use.