Communication satellite failed to reach geostationary orbit

This video shows a European Space Agency Ariane rocket that was launched earlier this week.  The rocket was carrying two satellites intended for geostationary orbit, the W3B satellite for French company Eutelsat and a satellite for Japanese company B-SAT corporation, called BSAT-3b.

There’s lot of information in the clip.  The commentator tells viewers about the liquid rocket fuels (hydrogen and oxygen), the water dousing system used at liftoff and explains each stage of the rocket’s journey presentation.

The French W3B satellite was designed to provide TV, radio and internet services to Europe, Africa and the Middle East.  At 13:11 in the film, we can see the release of W3B.  Notice that the left side of the screen shows an altitude of only 1,200km at this point. This is not high enough to achieve geostationary orbit and the satellite must use its own propulsion system to reach an altitude of 36,oookm.

Unfortunately, W3B experienced propulsion problems and was unable to climb to 36,000km.  There is a BBC news report of the mission failure here.  The photograph in the BBC article is particularly good because, although the satellite is wrapped in protective film, we can clearly see two curved reflectors wrapped in silver film.

Newton III in action – continued

This amazing footage of the Saturn V rocket launch for the Apollo11 moon landing mission has been put online by Mark Gray.  The video provides an extra dimension to the launch photograph in my earlier post about Newton’s 3rd law of motion.  While that picture shows an enormous plume of gas being forced out of each rocket exhaust, the video below demonstrates the heat of the gases and the effect they have on the structure of the launch pad itself.

Apollo 11 Saturn V Launch (HD) Camera E-8 from Mark Gray on Vimeo.

colour, temperature and emission spectra

Today we looked at emission spectra from different light sources; mercury, sodium, cadmium and oxygen discharge tubes, using a handheld spectroscope.

Here is a video that shows you how to make a basic spectroscope at home.  There are lots of guides like this online.  You might prefer to make a larger spectroscope by using a Pringles tub rather than an old toilet roll holder as the main tube.

I have attached the handout on colour and emission of light from different elements below.

ray diagram – object closer than 1f

This post is for Standard Grade and Intermediate 2.

Here we consider an object closer than one focal length.  You will see that it is not possible to obtain a real image when the object is this close to the lens.  On a ray diagram, a real image is one that is found on the other side of the lens from the object.

Real images can always be displayed on a screen – a projector in the cinema or classroom produces a real image.  If you are doing an experiment, you can check to see if an image is real using a piece of paper.  Move your sheet of paper closer to and further from the lens – if you can’t get an image to form on the paper then the image must be virtual.  When we look at an object up close through a magnifying glass, we see a virtual image.

ray diagram for objects closer than 1f from mr mackenzie on Vimeo.

how to draw a ray diagram

If you are sitting Credit Standard Grade or Intermediate 2 you should be able to draw a ray diagram for a convex lens.

At Standard Grade you must be able to draw this diagram for a magnifying glass.  A video for this will be posted shortly.

Intermediate 2 candidates may be asked to draw the diagram for an object placed

  • closer than one focal length
  • between one and two focal lengths
  • more than two focal lengths

from the convex lens.  I will post a video showing each of these three situations.

Let’s start with an introduction to drawing ray diagrams.  This video looks at an object between one and two focal lengths from the lens.  It will show you how to draw the diagram and explain the terms we use to describe the image.

how to draw a ray diagram from mr mackenzie on Vimeo.

Disclaimer: No rabbits were harmed in the making of this video.

Newton III in action

On Friday, we examined the importance of Newton’s 3rd law of motion.  In our discussions, different explanations for the motion of jets and rockets were proposed and considered.  The front runners were;

  1. at launch, the ground pushes back against a rocket
  2. during flight, air pushes back against a plane

Unfortunately, the lack of ground and air (or any other gas) meant that neither of these models were able to explain the propulsion of an object in space.  It was at this point we remembered Newton’s 3rd law of motion (or here with non-rocket examples) from Standard Grade.

You’ve got to be careful with Newton’s 3rd law of motion, it’s easy to get confused. Bonus question: What’s wrong with this explanation?

I found a photograph that provides a stunning visualisation of Newton’s 3rd law in action during the launch of a DeltaIV rocket.  You can read the details of setting up for this photo here.


image courtesy of Ben Cooper,

The photo was taken at very short range (about 30m) from the launch site and clearly shows hot gases being forced out of the exhaust at high speed. When a rocket forces out gas, the expelled gas pushes back on the exhaust with an equal force.  Since the exhaust is part of the rocket’s structure, the entire rocket is propelled in the opposite direction to the gas.

It is this pushing back on the exhaust that provides thrust for a rocket.  It doesn’t matter if the rocket is on the launch pad, in mid air or outer space. As long as it can push gas out of the exhaust, it will be able to propel itself forwards using Newton’s 3rd law of motion.

We don’t normally get a clear view of the hot gases being forced out of a rocket in launch photographs.  A lot of the smoke seen in images like the one shown below is actually steam.


NASA/courtesy of

There are two main sources of steam during launch.  The most obvious is the burning of fuels but NASA also soaks launch platforms with water just before and after launch so that the massive sound waves don’t damage the vehicle being launched.  There is a wikipedia article on the use of water during space shuttle launches.