## Car velocity physics – physics velocity

A physics professor drives along in his camry on the highway and covers about 88 feet per second or a velocity of 100 km/h when he observes a mitsubishi GT 3000 that races out onto the freeway.

This vehicle has an initial velocity of 100 km/h and smoothly accelerates, with the increase in velocity being constant over time, up to 250 km/h which is about 220 ft/s.

A police helicopter spots the GT 3000 and calls in squad car to lay a spike strip. The GT 3000 slams on the breaks and leaves skid marks for 160 feet. The police officer who finds the driver calmy whips out the stone tablet of THE TRUTH (v=v0 + at and x-x0 = v0 + 1/2 at2) and using this and his knowledge of the GT 3000’s breaking capabilities calculates the initial velocity and cuffs the driver for reckless driving.

The physics professor continues at a constant velocity on the highway, passes the arrest, and hears the driver cursing physics, but he knows the power of THE TRUTH.

## Derivatives and Differentials

Differentials and Derivatives

A. Letters u and v denote independent variables or functions of an independent variable; letters a and n denote constants.

B. To obtain a derivative, divide both members of the given formula for the differential by du or by dx.

Differentiation of Integrals:

If f is continuous, then

Chain Rule:

If y = f(u) and u = g(x), then

## Dimensional Analysis in Physics – Checking Answers

Dimensional analysis

Dimensional analysis allows a quick check of your answer by seeing if the units are correct.

An example would be if you are finding a distance by multiplying a speed by a time.  The units of distance are meters and the dimensional analysis of the product is [velocity*time] = [(m/s)(s)] = [m]

Google can do this automatically (with SI units) for an even faster check.

## Greek Alphabet

Greek letters surface all the time in physics, here are the 24 letters in capital and lower case, along with their names.

 Alpha α Α Beta β Β Gamma γ Γ Delta δ Δ Epsilon ε Ε Zeta ζ Ζ Eta η Η Theta θ Θ Iota ι Ι Kappa κ Κ Lambda λ Λ Mu μ Μ Nu ν Ν Xi ξ Ξ Omicron ο Ο Pi π Π Rho ρ Ρ Sigma σ Σ Tau τ Τ Upsilon υ Υ Phi φ Φ Chi χ Χ Psi ψ Ψ Omega ω Ω

## Sound Level Terminology

• Absorption Coefficient- Denoted by alpha (units of inverse meters) and “a” (dB/m). This constant measures the sound-absorbing ability of a material. The values go from about 0.01 for marble slate to almost 1.0 for the long absorbing wedges that are used in some anechoic sound chambers.
• Anechoic Sound Chamber- room in which the walls, ceiling, and floor all are covered with sound absorbing materials shaped to maximize sound absorption. Echoes effectively do not exist in such a chamber
• Decibel- logarithmic unit used to gage sound level. Subtracting three decibels translates to reducing the intensity by 50%. Human ears, however, perceive sound that is 10 times less intense as being half as “loud”. In other words, a difference of 10 dB will seem to be twice as loud or quiet.
• Hertz- unit of frequency (inverse seconds). AKA cycles/second.
• Infrasonic- sound lower than 20 hertz
• Medium- the material that something travels through
• Octave- difference in pitch equal to a doubling of frequency
• Threshold of pain- 120 dB- the level that goes from discomfort to pain and hearing loss
• Tone- a definite pitch
• Ultrasonic- frequencies about 20,000 Hz (20 kHz)

 Decibel Level Sound 10 Light Whisper 20 Soft Conversation 30 Normal Conversation 40 Light Traffic 50 Loud Conversation 60 Busy Office 70 Traffic, train 80 Subway 90 Heavy Traffic, Thunder 100 Jet Plane takeoff 120 Pain Threshold

## Golf Ball Physics

Golf Balls Have dimples on their surfaces to minimize drag (a force that dissipates when an object moves through a fluid).

A smooth ball causes the air to flow in such a way that the air “sticks” to the ball longer. The dimples also act to create backspin- which makes the air pressure on the top of the ball decrease- giving it lift (somewhat like the situation with an airplane’s wings).

A smooth ball that ravels 65 meters would travel something like 275 meters with dimples when hit with the same force.

Golf balls have 300-500 dimples that can be 0.25 mm deep.

## Absolute Zero

Absolute Zero also known as 0 degrees Kelvin or -273.15 degrees Celsius describes the theoretical temperature at which particles have zero thermal energy- meaning that velocity of the particles goes to zero. Thus the velocity of the particles corresponds to temperature.

Absolute Zero was, previously thought to be the temperature at which an ideal gas would decrease to zero volume. At lower temperatures the velocity of the particles is lower which corresponds to lower volume. It now finds use as the bottom of an absolute temperature scale.

The Low Temperature Laboratory in the Helsinki University of Technology, Finland reached 2 x 10^-9 degrees Kelvin in 1989.

## Google Math (with applications to physics)

The google search box can do some crazy things. One function is being a calculator. Try typing in 2+2

Basic stuff, right?

Well, it can go a bit beyond that. Next try typing in “seconds in a year”

An approximation for this, taught to me by Dr. Phil Kesten at Santa Clara University is pi * 10^7 seconds
Even more complex is typing in something like Avogadro’s number and multiplying it by the mass of a proton to get the approximate molar mass of Hydrogen

These functions were quite useful for calculations even in my physics classes. Play around with it, not everything will work, but many calculations will.