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MinutePhysics has a great video on Milkman, vomiting levitator: http://dft.ba/-vomphysics
Jetpacking was awesome fun! Despite the fat lip I had a great time. I think knowing a bit about physics actually helps fly the jetpack. It works on the same principle as a rocket (Newton’s 3rd law) but unlike the shuttle, you don’t carry your own propellant with you. Instead, water is pumped out of the lake by the jetski at up to 60 litres a second. It is then fired out of the nozzles at around 15 m/s creating 1800 N of force, the equivalent of about 150 fire extinguishers. On me this can produce acceleration of about 1.5g’s.
The world’s roundest object helps solve the longest running problem in measurement — how to define the kilogram.
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A kilogram isn’t what it used to be. Literally. The original name for it was the ‘grave’, proposed in 1793 but it fell victim to the French Revolution like its creator, Lavoisier. So begins the tale of the most unusual SI unit. The kilogram is the only base unit with a prefix in its name, and the only one still defined by a physical artifact, the international prototype kilogram or IPK.
But the problem with this definition has long been apparent. The IPK doesn’t seem to maintain its mass compared to 40 similar cylinders minted at the same time. The goal is therefore to eliminate the kilogram’s dependence on a physical object. Two main approaches are being considered to achieve this end: the Avogadro Project and the Watt Balance.
The Avogadro project aims to redefine Avogadro’s constant (currently defined by the kilogram — the number of atoms in 12 g of carbon-12) and reverse the relationship so that the kilogram is precisely specified by Avogadro’s constant. This method required creating the most perfect sphere on Earth. It is made out of a single crystal of silicon 28 atoms. By carefully measuring the diameter, the volume can be precisely specified. Since the atom spacing of silicon is well known, the number of atoms in a sphere can be accurately calculated. This allows for a very precise determination of Avogadro’s constant.
Special thanks to Katie Green, Dr. David Farrant, the CSIRO, and the National Measurment Institute for their help. Thanks also to Nessy Hill for filming and reviewing earlier drafts of this video.
There is debate as to whether this is truly the roundest object ever created. The Gravity Probe-B rotors are also spherical with very low tolerances such that they may in fact be rounder.
Music by Kevin McLeod (incompetech.com) Decision, Danse Macabre, Scissors
What happens when single photons of light pass through a double slit and are detected by a photomultiplier tube? In 1801 Thomas Young seemed to settle a long-running debate about the nature of light with his double slit experiment. He demonstrated that light passing through two slits creates patterns like water waves, with the implication that it must be a wave phenomenon.
However, experimental results in the early 1900s found that light energy is not smoothly distributed as in a classical wave, rather it comes in discrete packets, called quanta and later photons. These are indivisible particles of light. So what would happen if individual photons passed through a double slit? Would they make a pattern like waves or like particles?
Light is so common that we rarely think about what it really is. But just over two hundred years ago, a groundbreaking experiment answered the question that had occupied physicists for centuries. Is light made up of waves or particles?
The experiment was conducted by Thomas Young and is known as Young’s Double Slit Experiment. This famous experiment is actually a simplification of a series of experiments on light conducted by Young. In a completely darkened room, Young allowed a thin beam of sunlight to pass through an aperture on his window and onto two narrow, closely spaced openings (the double slit). This sunlight then cast a shadow onto the wall behind the apparatus. Young found that the light diffracted as it passed through the slits, and then interfered with itself, created a series of light and dark spots. Since the sunlight consists of all colours of the rainbow, these colours were also visible in the projected spots. Young concluded that light consist of waves and not particles since only waves were known to diffract and interfere in exactly the manner that light did in his experiment.
The way I have always seen this experiment performed is with a laser and a manufactured double slit but since the experiment was conducted in 1801 I have always thought that it should be possible to recreate the experiment using sunlight and household materials. That is basically what I did here. I will show the interference pattern I observed with my homemade double slit on 2Veritasium but I chose to use a manufactured double slit here to ensure that the pattern was impressive for observers at the beach.
Special thanks to Henry, Brady, and Rupert for their cameos, Glen for filming and Josh for helping create the apparatus. Thanks also to the Royal Society for allowing us to view the original manuscript of Young’s lecture and the University of Sydney for lending the double slits.
Music by Kevin Mcleod (incompetech.com) Danse Macabre, Scissors
Scientists are being inspired by nature to design the next generation of security devices. Arrays of nanoscale holes create beautiful reflected colours that are almost impossible to forge. This video was supported by TechNyou – check out their series on logical fallacies: http://bit.ly/WBsD31
Soon these nanoscale security devices could replace holograms. They are many times more reflective than holograms, and although the structures are smaller scale, they are lower aspect ratio and therefore easy to manufacture in bulk.
The electron wiggle simulation is from PhET, the best physics simulations ever: http://phet.colorado.edu
Special thanks to Thomas from Copenhagen who showed me around the city including the science museum where he assisted with the soap bubble demonstration.
Heisenberg’s uncertainty principle tells us that it is impossible to simultaneously measure the position and momentum of a particle with infinite precision. In our everyday lives we virtually never come up against this limit, hence why it seems peculiar. In this experiment a laser is shone through a narrow slit onto a screen. As the slit is made narrower, the spot on the screen also becomes narrower. But at a certain point, the spot starts becoming wider. This is because the photons of light have been so localised at the slit that their horizontal momentum must become less well defined in order to satisfy Heisenberg’s uncertainty principle.
Henry (MinutePhysics) has previously made a video about Heisenberg’s Uncertainty Principle where he treats it as less spooky and more a consequence of waves: http://bit.ly/TV3xO5
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Innovative research conducted in Lausanne, Switzerland has shown that a combination of neurotransmitters and electrical stimulation can restore movement to the lower limbs of previously paralysed rats. But in order for this motion to be made voluntarily the rats must be motivated to walk. This motivation comes in the form of cheering, visual cues, and of course, chocolate.
