Rhett Allain reports: Bob Riggle is 80 years old and he has a car. This car has a 2,500 horsepower engine mounted in the rear. But what happens when you have this much power? Yes, you can see in the video that there are two events. First, the car does a “wheelie” and second the car rolls over.
Fortunately no one was injured, but at least this is a great opportunity for a physics lesson.
Center of Mass and Wheelies
There are some forces acting on this car so let’s start with a diagram.
There are essentially three forces on the car in this case.
- The gravitational force pulls down. We can model this force as though it was only pulling down at one point. We call this point the center of mass (technically, it would be the center of gravity—but on the surface of the Earth these two points are at the same place).
- There is the force that the ground pushes up on the car. Since the car is not accelerating in the vertical direction, this ground force must be equal to the gravitational force.
- The friction force pushes on the tire at the point of contact with the ground. This force pushes the car in the direction that it is accelerating.
But how does this car stay tilted up like that? Shouldn’t the gravitational force make it fall back down? Clearly, it doesn’t. Perhaps the best way to understand this wheelie is to consider fake forces. We normally consider forces as interactions between objects (between the ground and the car or between the Earth and the car). However, it’s sometimes useful to create other forces that are due to accelerations. Now, these are fake forces in that they are not a real interaction. But as viewed in an accelerating reference frame (like inside the car), it is as though there is this real acceleration force.
Since the car accelerates to the left (in the above diagram), the fake force is to the right and keeps the car in wheelie up position.
But what about torque? If you want to rotate an object, you need torque. One expression for torque would be (this is just the scalar form—for simplicity):
In this expression, F is the force, r is the distance from the point of rotation to the point where the force is applied and θ is the angle between these two things. For the total torque about the wheel, it’s really just the torque due to the gravitational force and the torque due to the fake force.
If you put the engine in the front of the car (where it usually is) then the center of mass moves closer to the front. This means the gravitational torque will be much larger (since r is larger). If you get the center of mass closer to the back wheel, the torque from the fake force doesn’t need to be as high to get a wheelie. Read the rest of this entry »
LAUREL, Md. — Nola Taylor Redd reports: With less than 24 hours to go before NASA’s New Horizons probe makes its close flyby of Pluto, scientists are already learning more about the dwarf planet than ever before, including the fact that it is bigger than previously thought.
New Horizons’ latest views of Pluto have shown the dwarf planet to be 1,473 miles (2,370 kilometers) across, making it the largest body in the icy Kuiper Belt at the edge of the solar system. The observations also confirmed the presence of a polar ice cap on Pluto, and measured three of the dwarf planet’s moons.
“Pluto is not disappointing,” said principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado, during a NASA briefing here today (July 13).
As New Horizons closes in, the spacecraft made the most precise measurements to date of Pluto’s size using methods similar to those employed by NASA’s Voyager spacecraft. The new diameter of the dwarf planet makes it larger than fellow Kuiper Belt denizen Eris, which is 1,445 miles (2,326 km) in diameter.
Previous estimates for the size of Pluto had put its radius at 1,430 miles (2,301 km). But Pluto now stands as the undisputed king of the Kuiper Belt.
“This settles the debate about the largest object in the Kuiper Belt,” Stern said. Read the rest of this entry »
Isabella Steger reports: Hong Kong’s legislature is expected to vote down a proposal that would let the public directly elect the city’s chief executive in 2017 — but only from a prescreened slate of candidates. The showdown follows city-wide protests and a year and a half of efforts by Hong Kong’s leaders to sell the Beijing-backed election plan. Here are five things to know about the vote.
1. The Legislature Will Vote This Week
The proposal currently on the table will be put to a vote this Wednesday and Thursday. This is arguably the most critical of five stages in the election overhaul blueprint, laid down by Beijing and in accordance with the Basic Law, Hong Kong’s mini-constitution
2. Pro-Democracy Lawmakers Oppose the Package
The package lays out the rules for electing Hong Kong’s chief executive in 2017 within a framework formulated by Chinese authorities, in which all candidates must be nominated by a 1,200-member committee that is heavily pro-Beijing. After slight tweaks announced in April, the opposition maintains that the system is not democratic enough to allow one of their own candidates to stand.
3. The Plan Is Not Likely to Pass
27 pro-democracy lawmakers — who control a little more than one-third of the city’s legislature –say they will vote against the package, as has one lawmaker who isn’t part of the opposition camp. Read the rest of this entry »
PopMech Editors: Say hello to the shortest lunar eclipse of the century. These stunning photos capture the blood moon as captured over Colorado, China, and New Zealand. For more, check out our original post on the early morning event.
Undocking coverage lasts from 6:15 p.m. to 7:30 p.m. EDT, while landing coverage is scheduled to run from 9 p.m. to 11 p.m. EDT
Mike Wall reports: NASA will test-fire the booster of its Space Launch System (SLS) megarocket today at 11:30 a.m. EDT (1530 GMT), and three astronauts will return to Earth from the International Space Station in the evening. You can watch the space action live on Space.com, courtesy of NASA TV.
“What’s impressive about this test is, when ignited, the booster will be operating at about 3.6 million pounds of thrust, or 22 million horsepower. This test firing is critical to enable validation of our design.”
— Alex Priskos, manager of the SLS Boosters Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama
The SLS rocket booster test takes place at the facilities of aerospace firm Orbital ATK in Promontory, Utah, with webcast coverage beginning at 11 a.m. EDT (1500 GMT). There will be no spaceflight involved: Engineers will fire the 177-foot-long (54 meters) booster for two minutes on the ground, in a horizontal configuration.
“What’s impressive about this test is, when ignited, the booster will be operating at about 3.6 million pounds of thrust, or 22 million horsepower,” Alex Priskos, manager of the SLS Boosters Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, said in a statement. “This test firing is critical to enable validation of our design.”
Another booster test is planned for early 2016, NASA officials said.
The SLS will incorporate two of the five-segment boosters, as well as four RS-25 engines, on its first two flights, which will be capable of lofting 70 metric tons of payload to low-Earth orbit (LEO). NASA intends to scale the rocket up to deliver 130 metric tons to LEO, to enable manned missions to faraway destinations such as Mars. The first SLS flight is currently scheduled for 2018.
This evening, NASA astronaut Barry “Butch” Wilmore and Russian cosmonauts Alexander Samokutyaev and Elena Serova will wrap up their nearly six-month-long mission aboard the International Space Station and come back down to Earth. Read the rest of this entry »
The gift from Robert and Renee Belfer was announced as the institution celebrates its 50th anniversary this year.
An exhibition titled “A Roman Villa – The Belfer Collection” showcasing approximately 100 of the objects will be on view at The Israel Museum from June 5 through Nov. 21.
The collection is “one of the most important private holdings of antiquities anywhere,” museum Director James Snyder said in a telephone interview from Jerusalem…Read more
Je Suis Charlie Hashtag Makes Media History
The “Je Suis Charlie” hashtag has become one of the most popular in the history of Twitter as people around the world showed their solidarity for the victims of the Paris outrage.
At its height the tag was tweeted at a rate of 6,500 times a minute and featured in 3.4 million tweets in just one 24 hour period.
The phrase is in reference to the Charlie Hebdo magazine where 12 people were slaughtered when Islamist terrorists stormed their offices in Paris on Wednesday sparking a series of attacks lasting three days.
STICKIN’ IT TO THE MAN: ‘I refuse to comply with the requirements of my illegal detention under house arrest. The bracelet with some effort has been cut off with kitchen scissors’Posted: January 5, 2015
Putin Critic Alexei Navalny Defies House Arrest
Navalny received suspended sentence on 30 December for embezzling money but was not released from house arrest
Kremlin critic Alexei Navalny said on Monday he would no longer comply with the terms of his house arrest and had cut off his monitoring tag.
Navalny, who led mass protests against Vladimir Putin three years ago, was handed a suspended sentence on 30 December after being found guilty of embezzling money in a trial that led to his brother being jailed on similar charges.
“It is stupid to brag, but I am the first person in the history of Russian courts to be sitting under house arrest after the verdict.”
He was placed under house arrest almost a year ago during the investigation but said in a blog that he was perhaps the only person in Russian legal history to be kept under house arrest after being sentenced.
He said he should have been released after sentencing in late December but instead was being held pending the publication of the verdict on 15 January – a situation that even the police did not know how to deal with. Read the rest of this entry »
Public discontent in Hong Kong is at its highest for years
AFP reports: Thousands are expected to take part in a major pro-government rally in Hong Kong Sunday to counter a civil disobedience campaign that has pledged to paralyse the city in a push for electoral reform.
Public discontent in Hong Kong is at its highest for years, with concern over perceived interference from Beijing and growing divisions over how its leader should be chosen in 2017 under political reforms.
“We want to let the world know that we want peace, we want democracy, but please, do not threaten us, do not try to turn this place into a place of violence.”
— Alliance co-founder Robert Chow
Pro-democracy campaigners from the Occupy Central group have pledged to mobilise protesters to take over some of the busiest thoroughfares of the financial hub if public nomination of candidates is ruled out by the authorities.
FLASHBACK 2012: SCMP’s Benjamin Garvey, who more or less live-tweeted the proceedings, tweeted this photo and message: “Cameraman was hit from behind, other cameramen lept to his defence, grabbed attacker, held him until police came.”
But the movement has been heavily criticised by Beijing and city officials as being illegal, radical and violent.
[Also see – Hong Kong Asks Beijing for Greater Democracy]
Organisers of Sunday’s rally, the Alliance for Peace and Democracy, say the silent majority of the city’s seven million residents do not support the Occupy movement.
“We want to let the world know that we want peace, we want democracy, but please, do not threaten us, do not try to turn this place into a place of violence,” alliance co-founder Robert Chow told AFP.
More than 120,000 people have signed up for the rally, which started shortly after 1:30 pm (0530 GMT), but the turnout could reach up to 200,000, the alliance said. Read the rest of this entry »
WAM TOKYO, 5th May, 2014 (WAM) — A strong earthquake with a preliminary magnitude of 6.0 on the Richter scale struck Tokyo on Monday, the Japan Meteorological Agency said. No tsunami warning was issued for the 5:18 a.m. (2018 GMT Sunday) quake, the agency said.
According to the Kuwait News Agency, KUNA, at least 17 people were injured in Tokyo and its neighbouring prefectures, according to police and fire-fighters. There was no impact on nuclear power plants in the region, operators said. All subway systems in Tokyo and some train services linking central Tokyo and other cities were temporarily suspended after the quake, but resumed later.
The focus of the tremor was 162 km underground near Izu Oshima Island in the Pacific Ocean, about 120 km south of Tokyo, the Japan Meteorological Agency was quoted as saying. Read the rest of this entry »
Serious question: Is there a good argument for a president skipping a national security meeting on a day such as this?
— Charles C. W. Cooke (@charlescwcooke) March 1, 2014
The United Nations Security Council will be holding a closed door meeting for the second consecutive day to discuss the current situation in Ukraine.
The President of the Security Council said informal consultations among council members would begin at 2 p.m. (1900 GMT) Saturday. The council also held closed door consultations on Friday at the request of Ukraine’s U.N. Ambassador Yuriy Sergeyev who referred to “the deterioration of the situation” in the Crimean Peninsula which he said “threatens the territorial integrity of Ukraine.”
Russia’s parliament on Saturday approved a motion to use the country’s military in Ukraine after a request from President Vladimir Putin. Ukraine has already accused Russia of “a military invasion and occupation” of strategic points in the Crimean peninsula, a Ukrainian territory where Russia’s Black Sea fleet is based.
At least 15 people have been killed in a trolley bus blast in Volgograd, emergency services report, only a day after a suicide bombing ripped through the city’s railway station, killing 17.
Monday, December 30
“The emergency services have reacted very swiftly. All those injured have been taken to hospitals, as their identities are being determined,” he said.
05:37 GMT: According to witness reports to ITAR-TASS, there were many students on the bus.
“There was a loud ‘pop’, then a flash, everything was enveloped in smoke,” one female witness said, describing the sudden realization.
05:34 GMT: The Investigative Committee now puts the number of injured at 15.
05:30 GMT: In describing the character of the blast, ITAR-TASS law enforcement sources have said that it appears to be a suicide attack, “judging from the body fragments characteristic of such a bombing.”