What factors affect speed when traveling?
--
Drag from air or water (e.g. wind resistance), moving air or water (wind, current,
or waves)
-- Gravity, magnetism and friction.
-- Muscular
power, Mechanical power
-- Efficiency loses, both mechanical and muscular
--
Friction can be broken down into static, kinetic and molecular. Rolling
resitance is a combination of all three.
What are the effects of these factors?
Wind
Resistance
Wind resistance goes
up by a cube of speed. When you travel twice as fast, wind resistance
increases by a factor of eight. Wind speed in the direction of travel
will greatly change the amount of wind resistance you feel. If you have
a strong tailwind you will go faster, likewise a headwind will slow you down.
A strong crosswind will not change your forward travel speed much, but
you do expend some energy staying on course. Wind resistance is not very important for slow activities like walking
but makes a big difference when you are biking.
Air
Pressure & Air Density
Air pressure has
a slight effect on speed. Lower air pressure means you have less air to
push through, and will reduce wind resistance, but only a small amount.
Air pressure can differ because of altitude or weather. Bad weather
will lower air pressure and good weather increases air pressure.
Air density takes into account the gas constant and temperature as well as air pressure. The gas constant is determined mainly by the (viscosity of the) main components of the atmosphere. Low temperatures can raise air density while higher temperatures raise the air density. Temperature is measure in kelvins, a scale that starts at absolute zero. Celius is the same as the Kelvin scale but you add 273.13 to it.
http://www.sablesys.com/baro-altitude.html Altitude/barometric pressure table.
Air density is porportional to wind resistance. That means, if speed is kept constant, if air density doubles, so does wind resistance. Temperature is inversely porportional to wind resistance. From 20C to -20C, air density changes about 15%.
On Earth, atmospheric pressure can vary between 950 to 1050 hPa, a difference of about 10% because of weather. Bad weather reduces air pressure, and reduce wind resistance a small amount. Atmospheric pressure can go from 1013 hPa to 620 hPa at 4000 m, a difference of approximately 60% (or a 40% drop). 4000 meters is the alititude of the highest capital city of the world. This is change is large enough to notice if you were riding a bicycle, although you would have to deal with less oxygen available to breath. At 8000 meters is the highest mountains of the world with atmospheric pressures of 360 hPa. Here you need supplementary oxygen, and you would likely be mountain climbing and wouldn't notice the decrease in wind resistance.
Air pressure becomes more significant on other worlds. Some planets and most moons have an atmosphere so thin, it beats the best vacuums we can produce on Earth. On these worlds wind resistance is not a factor. On a bicycle, outrageous and very dangerous speeds can be reached.
On Titan, a moon of Saturn, has an atmosphere pressure 1.6 times that of Earth. However, Titan's force This atmosphere would feel much the same as the Earth, until you reach high speeds. Overall speed would drop about 18% when wind resistance is the main factor.
On Mars, the atmosphere is a hundred times thinner than Earth. To feel the same amount of wind resistance on Mars you would have to be going almost five times as fast.
On Venus, the situation is the opposite of Mars. Venus has an atmospheric pressure approximately ninety times that of Earth. Moving on Venus (assuming of course you have adequate protection from the intense heat and corrosive atmosphere) is almost like moving through water. It takes a lot of energy to get anywhere fast. Even a riding recumbent bicycle would have difficulty getting above 20 km/h. A car with maximum accleration might accomplish 100 km/h (?)
Water Resistance and Current Speed
Water is a medium like air. Only that water is much more difficult
to push through. It takes 773 times more energy to get through than air. Water resistance like wind resitance goes up by
a cube of the speed. Current speed, the water counterpart
of wind speed, affects water resistance in
the same way.
Water is so thick compared to the air that movement underwater with contact of the ground is extremely difficult. Walking underwater, assuming your buoyancy is low, is like walking in slow motion. Underwater mountain biking is just as slow. Because of this slowness it is much easier to simply swim though the water.
Gravity is a big factor in speed. When you are going uphill or jumping, you are fighting gravity. The steeper the hill, the more energy you must expend. When you are going downhill or free falling, gravity helps you.
On downhills, you will speed up until you hit terminal velocity. When you are going down a steep hill on a bicycle without pedaling, you hit terminal velocity within seconds. Terminal velocity is determined by the acceleration of gravity, air resistance and slope. [Slope energy to be linked]. Decrease gravity and terminal velocity will go down by the square root of gravity. Increase air resistance and the termainal velocity go down linerally. To describe the effect of slope requires a formula. At first a doubling of slope doubles terminal velocity, but this relation changes as angles get larger, and maxs out at 90 degrees -- freefall.
Magnetism is a force that rarely comes into play. In nature, it accounts for very little. Passing over magnetic rocks may slow you down, but the effect is so small it is practically non-existant.
The biggest use of magnetism is on maglev trains. These trains require a strong magnetic field for proplusion and leviatation. The major use of magnetism is for braking. http://www.dom.com/about/companies/vapower/maglev/propulsion.jsp http://www.magnetarcorp.com/faq.html Some brakes use permanent magnets, and because of that use no power, except for a small force to put the brakes into position. http://home.earthlink.net/~rivedu/14tesla.html. Or electromagnets could be used, apply a current and a powerful magnetic field is formed.
Some uses for magnetism are more pratical in lower gravities. Magnetic shoes to provide extra traction is one example. Leviation via diamagnetic replusion is practical only in lower g environment. Even though most things (people, water, etc) are slighly replused by a magnetic field, the field must be quite high for levitation. Leviating people is a challenge for today's technology.