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, Launchphotography.com

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 nasaimages.org

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.

momentum introduction from mr mackenzie on Vimeo.

We’ve just started to look at momentum in class.  There are 3 basic categories of interaction we will look at;

• inelastic collisions
• elastic collisions
• explosive collisions

Click on the <more> link after the 1st video to see the full list.

Int2 HW Q1a due 01/09/09 from mr mackenzie on Vimeo.

Higher HW Q2 due 02-09-09 from mr mackenzie on Vimeo.

Answer to HW Q3 due 01/09/09 from mr mackenzie on Vimeo.

answer to Higher HW Q4 02-09-09 from mr mackenzie on Vimeo.

answer to Higher HW Q5 02-09-09 from mr mackenzie on Vimeo.

For part (d), you need to mention air resistance slowing the human cannonball down. Reducing the horizontal component of velocity will reduce the range.

For Q1(b), you could select and two from each of the following lists.

Scalars: temperature, mass, distance, speed, energy

Vectors: force, acceleration, velocity, displacement

Download your own copy of the booklet for use at home by clicking on the link below.

You can watch the video using the player, click on the download button to save it to your computer or watch it in iTunes if you have subscribed to the podcast.

Vector Scale Diagrams from mr mackenzie on Vimeo.

If you want to improve the accuracy of your scale diagrams;

• use a sharp pencil
• measure the vector lengths as accurately as you can
• make sure the point of your vector arrow is on the end of the measured line
• start each new vector right at the tip of the previous vector

He’s shared another last minute example, this time it’s an internal resistance problem for Higher Physics.

To use the questions on your phone:

1. hit the download icon below to get the attached zip file on to your computer
2. unzip the file to reveal the jpg files inside
3. send the files to the picture folder on your phone* by bluetooth or usb

*make sure your phone displays them in numerical order, i.e. Q0010.jpg, then Q0011.jpg, etc. – otherwise you’ll get the answer before the question!

I had to send the files individually by bluetooth because my bluetooth program reversed their order.  You might need to check which order your bluetooth or usb transfer uses & send them in the wrong order to get it right on your phone.  Ask me if you’re still not sure how to do this.

Here’s a sample question:

Animated gif showing fission of U-235 by Stephan-Xp

We’ve discussed nuclear fission in class this week.  This is the process where an unstable nucleus splits into 2 or more smaller nuclei.  The new atoms produced are called daughter products of the fission process.  The University of California has a good animation of the fission process with commentary.  I have also included a link below to a nice animation from atomicarchive.com.

In the last part of the Higher course, we looked at the structure of the atom. Rutherford scattering of alpha particles fired at a very thin sheet of gold foil provided the evidence to develop our understanding of the atom from a “plum pudding” model to a “nuclear” atom – where most of the matter and mass are concentrated in the centre, or nucleus, of the atom.

There is a really good youtube video about Rutherford & alpha particle scattering -  watch the first 5 minutes only, it goes on to another topic after that. You can also follow the link below (the download link at end of post) to watch an animation of the alpha particle scattering experiment and follow how the results changed our view of the atom.

4(b) The critical angle is the angle of incidence that gives an angle of refraction of 90 degrees.  Beyond this angle of incidence, no refraction takes place and all light undergoes total internal reflection.

Answer to 2(b) attached as video.

Use the “more” link underneath the 1st video player to display the full set of answers.

Higher HW Q1a due 24/04/09 from mr mackenzie on Vimeo.

Higher-HW-Q1b due 24/04/09 from mr mackenzie on Vimeo.

Higher HW Q2b due 24/04/09 from mr mackenzie on Vimeo.

Higher HW Q2c due 24/04/09 from mr mackenzie on Vimeo.

Higher HW Q3a due 24/04/09 from mr mackenzie on Vimeo.

Higher HW Q3b due 24/04/09 from mr mackenzie on Vimeo.

Higher HW Q4a due 24/04/09 from mr mackenzie on Vimeo.

whole course notes

unit 1 summary (PowerPoint)

unit 1 revision notes (pdf)

notes on vectors (pdf)

St. Kentigern’s Academy revision notes: units 1.1 & 1.2,  1.3 & 1.4 and  1.5 & 1.6 there is also a  revision test and you can check your answers.

XPhysics unit 2 revision

TPD, EMF and internal resistance 

Unit 2 summary (Powerpoint)

Whole course summary notes (pdf)

St. Kentigern’s Academy Notes:  unit 2.1,  unit 2.2,  unit 2.3,  unit 2.4,  revision questions,  answers to revision questions

I found an useful simulation of the photoelectric effect here.  You can change the metal under investigation (we used Zinc in class).  You can also vary the wavelength and irradiance of the light.   Notice that below the theshold frequency you can’t get  any photoelectrons, even if you set the light to its brightest setting.

This video is also attached as a podcast.

Q1b due 06.03.09 from mr mackenzie on Vimeo.

Q1c due 06.03.09 from mr mackenzie on Vimeo.

Q3a due 06.03.09 from mr mackenzie on Vimeo.

Solution to Q3(b) – differential amplifier from mr mackenzie on Vimeo.

(i) the input current is zero (i.e. it has infinite input resistance)

and 

(ii) there is no potential difference between the inverting and non-inverting inputs (i.e. both pins are at the same potential)

(c) see attached.

(d) The op amp is unable to provide an output voltage greater than its power supply voltage. In practice, this saturation occurs around 15% below the supply voltage.

(a) The op amp is operating in the inverting mode.

(b) see attached file

• motion – SG transport, Int2 unit1, Higher unit1, AH unit1
• electricity – SG using electricity, Int2 unit1, Higher unit2, AH unit2
• light and sound – SG health physics, Int2 unit3, Higher unit3, AH unit3
• electronics – Int1 applied practical electronics, SG electronics, Int2 unit2, Higher unit2

They also have some chemistry products you might find helpful.

The software is free but you can only use it at home.  Why not download it and see if you find it useful.

Use the link below to try using the virtual oscilloscope I had on the SMARTBoard.  You can view different signals by connecting different coloured leads to the inputs.

www.virtual-oscilloscope.com