NEUTRINOS

If you missed Stephen Parke on the National Programme on Saturday, you can listen to his interview here

THE ELEGANT UNIVERSE (PART ONE)

An entertaining and accessible documentary about string theory (amongst other things).



This is intended just as a "trailer": you can see the entire programme at the PBS website

TARANAKI TECH AT OTAGO

On a recent visit to Otago University's Physics Department I was pleased to see one of Ecoinnovations' generators being used in the energy research laboratory.
Mike Lawley makes these generators in Taranaki from Fisher & Paykel "Smart-Drive" washing-machine motors.

NEW ZEALAND FROM THE SPACE SHUTTLE

Enjoy this photograph, which the space shuttle commander took for NPBHS student Charley Miles. Space shuttle on the left (tail fin pointing towards Earth) New Zealand on the right!

This makes a superb desktop image.

Click on the photo for the full version.

GEISSLER TUBE

This is a discharge tube. It consists of a partially-evacuated chamber containing an inert gas at low pressure. If a high Voltage (we used an induction coil) is applied across the terminals, the Voltage will strip electrons from the anode and create a stream of electrons. The electrons interact with the gas atoms, producing a visible beam of light.







Now if a magnet is brought close to the tube, the beam of electrons will deflect (moving charge in a magnetic field) and because this deflection is at right-angles to their motion, they move in a circular path.

The closer the magnet, the stronger the magnetic field and the greater the deflection. The force on a moving charge in a magnetic field is F=Bqv .

NPBHS CREST IN SPACE

The NPBHS tiger-jacket crest presented to NASA by Charley Miles in 2006 is currently in space, aboard the shuttle.
TVNZ Video:

Thin Lens Java applet

Have a look at this java applet that simulates spherical lenses and mirrors. Thin Lens Java applet

CHAMPAGNE SPARKLY EFFECT

Total internal reflection can also be seen in a stream of water. By shining laser light through Gladwrap into a stream of water we simulate the fibre optic cable, using water instead of glass. The laser light reflects off the water/air interface and stays inside the stream of water.

REFRACTIVE INDEX & TOTAL INTERNAL REFLECTION

By sending a narrow beam of light through a perspex block, you can easily see the refraction (bending) of the light as it re-enters the air. This is called refraction. As the light speeds up as it emerges from the block, its wavelength increases and the angle with the normal also increases.








Now if we increase the angle of incidence, we begin to see a lot more reflection, as the light begins to strike the tiny irregularities on the perspex/air interface at angles greater than the critical angle.












Finally, if we increase the angle of incidence so that all the lght strikes the perspex/air interface at an angle greater than the critical angle. we see the phenomenon called
Total Internal Reflection

Students collect data for a large number of incident and refracted angles and use MSExcel spreadsheets to calculate the sines of these angles.

Angle in perspex=P

Angle in air=A

Because SineA/SineP is the refractive index of perspex relative to air, a graph of SineA vs SineP will have a gradient equal to the refractive index of the perspex.

Using a data-projector the resulting graph can be shown to other students.

Good experimental practice results in a good fit to the regression line!

BALLISTIC PENDULUM

The ballistic pendulum consists of a suspended block which is struck by a fast-moving projectile. It is an example of "combined mechanics" meaning that it involves physics concepts from a range of topics.
The topics are:
conservation of momentum (when the slug hits the block)
conservation of energy (when the block rises up after being struck by the slug).
Data collected by 12PHYMC classes:
Mass of slug = 0.50g
Mass of block = 252.0g
Height change of block after being struck = 6.0mm.


Calculations
As the block moves upwards, kinetic energy is converted to potential energy
½mv²=mg∆h
=> v=√(2g∆h)
=> v=√(2*10*0.006)=0.3464m/s
So we now know the block had momentum immediately after being struck of 0.2525*0.3464=0.08747kgm/s.
As the block had no momentum before being struck, this must also be the momentum of the slug immediately before it hit the block.
So now we can work out the size of the slug's velocity:
ρ=mv
=>v=ρ/m=0.08747/0.00050=174.9m/s (170m/s to 2 sf)

Ballistic pendulum
Video sent by johnmc2

NASA SPACE SCHOOL

Akshay and Leela were interviewed by the Daily News yesterday and their story appeared on page two of this morning's edition. Congratulations to these NPBHS and NPGHS students on being selected to represent us at the NASA Space School later this year.

Photo: Daily News

MOMENTUM PROBLEM

LEN LYE

Not really about physics (any more than anything isn't!) but this picture is historically interesting, especially to residents of New Plymouth. It shows Len Lye (in black) attempting to erect an early (12m) version of his famous "Windwand" in New York in 1960. The technology back then simply wasn't up to Lye's vision. Now you can see a 45m Windwand on the New Plymouth foreshore. Lye's sculptures show an instinctive understanding of physics: if you get the chance, go and see his works. They are particularly interesting to students studying harmonics and wave-forms. The gentleman assisting him in the photo, wearing a white suit, is the English writer Robert Graves (author of "Goodbye to All That" and "I, Claudius"). In 1942 Robert Graves' daughter Catherine married the New Zealand nuclear physicist Dr. Clifford Dalton, who was later to invent the fast-breeder reactor. After Dalton's death in 1961, Catherine alleged that he had been murdered for his part in breaking the American monopoloy on nuclear technology, and even that the death of another New Zealand-born physicist, Dr. Gilbert Bogle, in 1963 was part of a cover-up to prevent Bogle from investigating Dalton's death. However it is generally accepted that Dalton died of cancer, and that Bogle's mysterious death beside a Sydney river was probably caused by hydrogen sulphide poisoning.

IMPULSE (CHANGE IN MOMENTUM)

When a force acts on an object for a period of time, it will change the object's momentum.
This quantity (change in momentum, or the product of force and time) is called IMPULSE.
We can easily derive a formula from Newton's second law. F=ma
a=Δv/Δt so F=m Δv/Δt
gives FΔt=mΔv
mΔv is the change in momentum, Δρ
In your textbooks the formula is given as FΔt=Δρ.

CENTRIPETAL FORCE (YR12)

The Yak 'planes looping over New Plymouth demonstrate circular motion.
Circular motion requires a centripetal force, which is a force directed towards the centre of the circular motion. This force is provided by the control surfaces of the aircraft pushing against the air, and by the aerofoil effect (lift) of the wings
At the top of the loop, gravity will provide some of the centripetal force, so the pilot will feel some "weightlessness"; but at the bottom of the loop, the 'plane has to have enough lift to overcome gravity and provide the necessary centripetal force and the pilot will experience a strong upward force from the seat, making him feel "squashed down".

Looping is also interesting from an energy perspective.
As the 'plane climbs into the loop it loses kinetic energy and gains gravitational potential energy. It needs enough kinetic energy at the bottom, to supply the potential energy at the top, and still have enough kinetic energy to keep flying.