News

Galileo Galilei presents his telescope (1609)

posted Tuesday, 25 August 2015

Galileo Galilei presented his telescope to the Venetian Senate on this day in 1609.

physics.info/news/?p=4355

Voyager 2 reaches Neptune (1989)

posted Tuesday, 25 August 2015

Voyager 2 made its closest approach to Neptune on 25 August 1989. It is the only space probe to have visited this planet so far. Voyager 2 is one of five space probes currently on a solar system escape trajectory.

full globe image of neptune

physics.info/news/?p=4384

Voyager 2 reaches Saturn (1981)

posted Tuesday, 25 August 2015

Voyager 2 made its closest approach to Saturn on 25 August 1981. It was the second space probe to have visited this planet. Voyager 2 is one of five space probes currently on a solar system escape trajectory.

physics.info/news/?p=4385

Canopus: First French thermonuclear weapon test (1968)

posted Monday, 24 August 2015

Date: 24 August 1968 (8:30 AM Tahiti Time)
Code Name: Canopus
Type: two-stage fusion
Yield: 2.6 million tons of TNT
Location: Fangataufa Atoll, French Polynesia

physics.info/news/?p=1788

Viking 1 launched (1975)

posted Thursday, 20 August 2015

Viking 1 with rockets burning, just seconds after launch

physics.info/news/?p=2586

Voyager 2 launched (1977)

posted Thursday, 20 August 2015

Voyager 2 launched from Cape Canaveral, Florida aboard a Titan-Centaur rocket on 20 August 1977. It visited Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. It passed the termination shock (the point where the solar wind slows abruptly to subsonic speed) in 2007. Voyager 2 original mission was to explore the outer planets, but it is now essentially an interstellar space probe.

date pioneer 10 pioneer 11 voyager 1 voyager 2 new horizons
1972 03‑03 launch
1973 04‑06 launch
" 12‑03 jupiter
1974 12‑04 jupiter
1977 08‑20 launch
" 09‑05 launch
1979 03‑05 jupiter
" 07‑09 jupiter
" 09‑01 saturn
1980 11‑12 saturn
1981 08‑25 saturn
1986 01‑24 uranus
1989 08‑25 neptune
1995 11‑30 last signal detected
1998 02‑17 passes pioneer 10
2002 04‑27 last message received
2003 01‑23 last signal detected
" 02‑07 contact attempt
2004 termination shock (94 AU)
2006 03‑04 last contact attempt
2006 01‑19 launch
2007 02‑28 jupiter
" termination shock (84 AU)
2015 07‑14 pluto
Timeline of Interstellar Space Probes NASA Mission Websites: Pioneer, Voyager, New Horizons

physics.info/news/?p=4382

Sputnik 5 launched (1960)

posted Wednesday, 19 August 2015

Sputnik 5 was launched on 19 August 1960 with the dogs Белка (Belka), which means squirrel, and Стрелка (Strelka), which means arrow, 40 mice, 2 rats and a variety of plants on board. The spacecraft returned to earth the next day and all animals were recovered safely.

physics.info/news/?p=4381

The Long, Lonely Leap (1960)

posted Sunday, 16 August 2015

Fifty-five years ago in August …


Life Magazine Cover

An hour and thirty-one minutes after launch, my pressure altimeter halts at 103,300 feet. At ground control the radar altimeters also have stopped on readings of 102,800 feet, the figure that we later agree upon as the more reliable. It is 7 o’clock in the morning, and I have reached float altitude.

At zero count I step into space. No wind whistles or billows my clothing. I have absolutely no sensation of the increasing speed with which I fall.

Though my stabilization chute opens at 96,000 feet, I accelerate for 6,000 feet more before hitting a peak of 614 miles an hour, nine-tenths the speed of sound at my altitude. An Air Force camera on the gondola took this photograph when the cotton clouds still lay 80,000 feet below. At 21,000 feet they rushed up so chillingly that I had to remind myself they were vapor and not solid.

Joseph Kittinger

For most skydivers, the acceleration experienced while falling is not constant. As a skydiver’s speed increases, so too does the aerodynamic drag until their speed levels out at a typical terminal velocity of 55 m/s (120 mph). Air resistance is not negligible in such circumstances. The story of Captain Kittinger is an exceptional one, however. At the float altitude where his dive began, the Earth’s atmosphere has only 1.5% of its density at sea level. It is effectively a vacuum and offers no resistance to a person falling from rest.

The acceleration due to gravity is often said to be constant, with a value of 9.8 m/s2. Over the entire surface of the Earth up to an altitude of 18 km, this is the value accurate to two significant digits. In actuality, this "constant" varies from 9.81 m/s2 at sea level to 9.75 m/s2 at 18 km. At the altitude of Captain Kittinger’s dive, the acceleration due to gravity was closer to 9.72 m/s2.

Given this data it is possible to calculate the maximum speed of Captain Kittinger during his descent. First we will need to convert the altitude measurements. To save calculation time we will only convert the change in altitude and not each altitude. Given that he stepped out of the gondola at 102,800 feet, fell freely until 96,000 feet, and then continued to accelerate for another 6,000 feet; the distance over which he accelerated uniformly was…

102,800 − 96,00 + 6,000  = 12,800 feet
  12,800 feet   1,609 m  = 3900 m  
1 5,280 feet

It’s now just a matter of choosing the correct formula and plugging in the numbers.

v0 =  0 m/s v =  ??
a =  9.72 m/s    
Δs =  3900 m    
   
v2 =  v02 + 2aΔs
v =  √(2aΔs)
v =  √(2(9.72 m/s2)(3,900 m))
v =  275 m/s

This result is amazingly close to the value recorded in Kittinger’s report.

614 mile   1,609 m   1 hour  = 274 m/s
1 hour 1 mile 3,600 s

As one would expect the actual value is slightly less than the theoretical value. This agrees with the notion of a small but still non-zero amount of drag. This number is another world record — the fastest speed attained by a human without the use of an engine.

Excerpted from Falling Bodies – Practice – The Physics Hypertextbook.

physics.info/news/?p=4386

Northeast Blackout (2003)

posted Friday, 14 August 2015

A widespread power outage that affected parts of Michigan, Ohio, Ontario, Pennsylvania, Maryland, New York, New Jersey, Connecticut, and Massachusetts began at approximately 4:10 PM on 14 August 2003. By 4:13 PM 55 million people in the US and Canada were without electric power. This is sometimes thought of as the "Third New York City Blackout". The first was in 1965 and the second in 1977.

physics.info/news/?p=1774

Four stroke engine patented by Nicolaus Otto (1877)

posted Friday, 14 August 2015

US patent number 194047 was issued to Nikolaus August Otto of Deutz, Germany on 14 Aug 1877. Otto’s engine is the type that powers most autos today.

physics.info/news/?p=1772