Why is centrifugal force ‘fictitious’?

December 27, 2016 Leave a comment

Centrifugal forces only arise when you treat a non-inertial frame of reference as if it were an inertial frame of reference. Consider what happens if I accelerate past a stationary object and I consider the motion of the object in a frame of reference in which I am at rest. I observe the object accelerate in the other direction. Since the mass of the object is constant, and Newton’s 2nd law gives F = ma, the fact that the object accelerates leads me to conclude that there must some force accelerating it. The same happens if I am in a bus which is accelerating (either by changing speed in the same direction or by changing direction). I witness the stuff, including me, accelerating around the bus but only because I am considering the bus and its contents as at rest in an inertial frame of reference.

Should you teach skills? An excellent case in favour from Geoff Petty

December 6, 2016 Leave a comment

We have a lot to learn about how other countries learn

December 6, 2016 Leave a comment

Take a look at @TheEconomist’s Tweet: https://twitter.com/TheEconomist/status/805955021070331904?s=09

Nested loops: looking for duplicates in arrays

December 1, 2016 Leave a comment

A and B are arrays of integers. Construct code to output all of the values that are in both A and B.

With questions like this, imagine you had to do it manually. Imagine you have two long lists of numbers on paper. How would you find all the values that occur in both lists?

You would probably look at the first number from list A and then scan all the way down list B to see if it’s there. If it was you’d make a note of it. Then you would get the next number from list A and do the same thing.

A computer algorithm will do exactly the same thing.

In pseudocode this is:

loop I from 0 to A.length - 1
  loop J from 0 to B.length - 1
    if A[I] = B[J] then
      output A[I]
    end if
  end loop
end loop

In Java it is:

for (int i = 0; i < a.length; i++) {
  for (int j = 0; j < b.length; j++) {
    if (a[i] == b[j]) {

Towards the end of the semester…

November 29, 2016 Leave a comment
  • You have three lessons to work on and complete your Greenfoot games.
  • We have ICARE next week.
  • Does anyone know what the plan is for the Friday of next week?
  • We will do a peer review on Tuesday of the last week of the semester in which you will play and judge each others’ games according to a set of criteria.

Basic Java Class Structure

November 28, 2016 Leave a comment

Basic knowledge for IB Computer Science is the structure of a Java class. You should be able to create the class, its instance variables, constructor, get and set methods, and a toString() method, without even need to stop and think.


Create a Point class that has two instance variables x and y, corresponding to its coordinates on the Cartesian plane. Include an appropriate constructor that initialises these variables. Encapsulate the variables and provide a toString() method.


public class Point {
   private int x;
   private int y;

   public Point(int x, int y) {

   public int getX() {
      return x;

   public int getY() {
      return y;

   public void setX(int x) {
      this.x = x;

   public void setY(int y) {
      this.y = y;

   public String toString() {
      return "(" + x + "," + y +")";

Block E Groups for Speed of Sound Experiment

November 14, 2016 Leave a comment

Group 1a
Nicolas, Aspen
Ottiger, Sebastian
Hwang, Do-Sung
Do, Nguyen

Group 1b
Seol, Subin
Hermans, Samuel
Sy, Russel Gabriel
Khoury, Alexander

Group 2a
Radhakrishnan, Harini
Cheon, Sae Joon
Lee, Byeong Cheon
Banwari, Ashwin

Group 2b
Siguion Reyna, Juan Antonio
Bantigue, Manuel Jerico
Halum, Kim Trevor
Hadaway, Katherine