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
Equation
time = distance——————velocity
t = d—v
1.2
Light year
Light year = distance light travels in a year
= 9.46 • 10^{12}km
For more information, check out the following website:
Speed and Velocity
Now Try This!
The nearest bright star beyond our sun is called Alpha Centauri. It is easily visible in the night sky if you live on Earth’s southern hemisphere. Alpha Centauri is orbited by a planet, the nearest one beyond our solar system.
Alpha Centauri is 4.37 light years away. That doesn’t sound too far until you remember that one light year = the distance light travels in a year which is about 10 trillion kilometers! So, Alpha Centauri is about 44 trillion kilometers away (give or take a few billion). How long would it take to travel to Alpha Centauri flying in the Space Shuttle going 28,000 kilometers per hour?
Left: Alpha Centauri: The nearest bright star beyond our sun at 4.37 light years away. Photo from ESO/Digitized Sky Survey 2.
Remember v = d/t? Rearrange that equation to find t:
time =distance——————velocity t = d—v
The distance of 44 trillion kilometers is too big to write out so we use scientific notation. As the Appendix shows a trillion is 10^{12} so
44 trillion km = 44 x 10^{12} km
but remember in scientific notation there is only one digit before the decimal so the distance, d, is 4.4 x 10^{13} km
And converting the velocity of 28,000 km/hr to scientific notation requires putting a decimal point after the 2 and counting over 4 spaces to the rightmost digit.
28,000 km/hr = 2.8 x 10^{4} km/hr
Now we are ready to do the problem!
t = 4.4 x 10^{13} km/2.8 x 10^{4} km/hr = 1.6 x 10^{9} hr
and since there are 24 hrs/day x 365 days/yr = 8,760 = 8.76 x 10^{3} hrs in a year,
1.6 x 10^{9} hr / 8.76 x 10^{3} hr/yr = 1.8 x 10^{5} = 180,000 years to reach the star!
Clearly, a faster vehicle is required if humans are ever going to travel to the stars!
Answer: No
No. Human space travel to stars requires a warp drive from science fiction. Otherwise, the immense distances between stars means that any rockets we have today would take far longer than not just the human lifespan, but the entire span of human evolution.
Answer: 4.37
Remember, a light year is distance light travels in one year, so light year distance = travel time in years when travelling at speed of light.
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