Top ten facts about gravity
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Gravity is the weakest of the four fundamental forces of nature but it is also the most impactful on your day-to-day business. Every time you drop a pencil or an apple lands on your head, gravity keeps your feet firmly planted to the ground. But the strength of gravity varies across the cosmos and the gravitational pull we are used to on Earth is weaker on a smaller and less heavy world like the Moon.
When Sir Isaac Newton proposed his laws of gravitation in the 17th century, he argued every body in the universe with mass will attract one another.
This force of attraction is directly proportional to the product of their mass and inversely proportional to the square of the distance between them.
In other words, all objects that have mass have a gravitational field surrounding them, and the heavier something is, the stronger is gravitational pull.
Albert Einstein would many years later expand on the theory of gravity, arguing it is a product of objects with mass curving or warping time and space itself.
A team of researchers from the University of Vienna and the Austrian Academy of Sciences have now measured the gravitational field of a gold sphere measuring just 2mm across.
The breakthrough, which was published in the journal Nature, is the first time scientists have demonstrated these forces in a laboratory.
Tobias Westphal, the study’s lead author, said: “According to Einstein, the gravitational force is a consequence of the fact that masses bend spacetime in which other masses move.
“So what we are actually measuring is how a ladybug warps space-time.”
In a vacuum, all objects near the Earth’s surface will accelerate towards the ground at the same speed – 9.8m per second.
On the Moon, objects will fall about six times slower because the satellite is about 80 times lighter than our planet.
On a ladybug, objects would fall about 30 billion times slower than on Earth.
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The breakthrough was made possible thanks to an experiment carried out towards the end of the 18th century by the English physicist Henry Cavendish.
In Newton’s time, scientists reserved gravity for the biggest of objects – stars and planets.
Cavendish was among the first to show even objects on Earth generate their own gravitational field.
He did so in 1797 by using a so-called torsion pendulum device to measure the field of a lead ball weighing 352 pounds (160kg) and measuring 30cm across.
The pendulum was made of two masses on the end of a rod suspended from a thin wire to allow it free rotation.
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The Vienna researchers recreated the experiment but on a miniature scale.
Instead of a big and cumbersome object, they used a 2mm gold sphere weighing a measly 90 mg.
The torsion pendulum was made from a 4cm glass rod only half-a-millimetre thick, suspended from a glass fibre only a few thousandths of a millimetre across.
Jeremias Pfaff, one of the researchers involved in the study, said: “We move the gold sphere back and forth, creating a gravitational field that changes over time.
“This causes the torsion pendulum to oscillate at that particular excitation frequency.”
The resulting movement is only a few millionths of a millimetre but could be precisely measured with lasers.
And to minimise the impact of external influences, the researchers conducted their experiment in the dead of night and during the holidays.
Co-author Hans Hepach said: “The largest non-gravitational effect in our experiment comes from seismic vibrations generated by pedestrians and tram traffic around our lab in Vienna.
“We, therefore, obtained the best measurement data at night and during the Christmas holidays, when there was little traffic.”
The scientists are hopeful the breakthrough will open up new possibilities in the hunt for dark matter – the most elusive source of gravity in the universe.
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