Air resistance and Levels of Detail in Physics

May 10, 2009

Somewhat similarly to friction, air resistance also acts as a retarding force.
The real world is not the same as idealized beginning physics situations; for example, projectiles will not follow the path of a parabola, unless they are in a vacuum.
Also, this air resistance is not a constant value, but instead it is proportional to velocity.
In [...]

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Rocket Explosions, Probability, and Compound Interest

May 9, 2009

If there are 1000 parts for a space shuttle and each of them has a 99.9% chance of working, then the chances for no malfunction at all is only about 37%.
By multiplying .999 by itself 1000 times without rounding, the true result is found, but if each time it had been rounded up a crew [...]

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Momentum and Momentum’s SI Units

May 8, 2009

There is something in physics that does not have a special name like a Newton or a Joule.
It is momentum and can be expressed as mass multiplied by velocity (kg*m/s).
Like energy and matter, momentum is conserved.
If you shoot a gun, there will be a recoil; the bullet goes forward and there is also a force [...]

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Path Independence and Thermodyanamics

May 2, 2009

Earlier in the year we said that the work necessary for hiking up the slope of Rampina Mountain vs. climbing straight up the cliff route would be the same, independent of the path taken.
This statement is true if you disregard friction and other factors, but one path has a greater length and more friction will [...]

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Heat Flow

May 1, 2009

Heat naturally flows from warmer to cooler.  Things tend towards equilibrium.
Therefore heat vents are most efficiently placed on the floors of rooms so the heat might rise up throughout the room.
If the vents were on the ceiling, then all the heat would stay towards the top of the room.
And fans are then placed on the [...]

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Latent Heat of Fusion | Latent Heat of Evaporation

April 30, 2009

If you add heat to some substance it will not necessarily change temperature.
Energy also can work towards producing a phase change, such as from solid to liquid or liquid to gas.
Water might heat up and change temperature or some portion of it might turn instantly to steam, leaving the rest of the water at the [...]

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What is Heat? And Heat Transfer

April 29, 2009

The term heat refers to the flow of energy.
If you drank a cool drink, it would only cool you down the difference in temperature for that amount you drink.
The liquid is brought into your system and therefore will warm up to your body temperature, while your body correspondingly cools down a little bit.
Different materials have [...]

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How a Thermostat Works, Thermal Expansion Coefficients

April 28, 2009

A good thermostat will accurately measure the environment while simultaneously not greatly changing its surroundings.
The basic construct that that makes a non-digital thermostat work is that a bimetallic strip has two layers of different metals.
The two coefficients of thermal expansion will be different, so because the two layers are connected, the thermostat will bend in [...]

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Speed of Light and Relative Speed

April 27, 2009

If Spaceman Spiff attaches a flashlight to the front of his spacecraft the light is still going to travel at the speed of light c.
Likewise if he attaches a loudspeaker to his ship in order to yell at aliens, those waves will travel at the speed of sound.
While a military plane going mach five (five [...]

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Decibels, Loudness

April 26, 2009

When someone returns from a heavy metal concert they don’t usually comment loudly about how many Watts per meter squared they experienced.
Decibels might make sense.  People tend to know that 120 Decibels is a lot.
This system has been devised and units of decibels measure perceived loudness.
It increases on a logarithmic scale, so something that seems [...]

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