I have seen a few simulations for apparent depth but was not satisfied with them. So I created this from scratch for use in tomorrow’s lesson. The positions of the eye and image of the fish are adjustable. It is more challenging to design for the actual fish to be draggable, so I only could allow the image to be dragged and hence, use it to shift the position of the actual fish.
This applet allows for students to visualise the conditions under which a reflection can be seen in a mirror. When the mirror is too short, for instance, the point of reflection does not lie on the mirror so light cannot be reflected.
Imagine one glass of D20 generating 9 GWh of electrical energy – enough power for a home for 865 years, at a cost of 1 cent per kWh. If successful, it will be a significant source of green energy in the next 10-20 years.
More importantly, nuclear fusion energy could potentially address the fears of many with regards to nuclear fission energy, such as the possibility of catastrophic meltdowns, weaponisation of raw material and environmental impact of mining and disposing of nuclear waste. This is because nuclear fusion reactions are self-limiting in that the reactors will shut down automatically if the optimal conditions are not maintained.
I can’t wait to see this happen, if it happens. Other than solving much of the world’s energy problems, it will also open up new opportunities in the energy sector for scientists and engineering. In fact, Helion itself is recruiting quite aggressively now.
It is a common misconception for students to assume that when a book is placed on a table, its weight and the normal contact force acting on it are action-reaction pairs because they are equal in magnitude and opposite in direction.
While we can emphasise the other requirements for action-reaction pairs – that they must act on two different bodies and be of the same type of force – I have tried a different approach to prevent this misconception from taking root. After reading this article on the use of the system schema representational tool to promote understanding of Newton’s third law, I tried it out with my IP3 students.
The system schema identifies the bodies in a question and represents them with shapes detached from each other to give space to draw the connecting arrows between them. The arrows must be labelled with the type of force, either by coding them (e.g. r for reaction force, g for gravitational force) or in full.
Every force will be drawn as a double-headed arrow between two bodies to represent that they are action-reaction pairs. It is important for students to understand that every force in the universe comes in such a pair, and the system schema can help them visualise that. If there is a force without a partner, it just means the system is not in the frame yet.
The next step to using the system schema is for students to isolate the object in question and draw its free-body diagram. Each force vector in the diagram should be accompanied by a name that includes: 1. the type of force and 2. the subject which exerts that force on the object.
The effectiveness of this method of instruction is clearly presented in the paper mentioned above, as performance on the force concept inventory’s questions on the third law saw an improved average from 2.8 ± 1.2 to 3.7 ± 0.8.
This is a common example used in the JC1 topics of Oscillations, where if one were to look at an object moving in circles from the side view, it will appear to move in simple harmonic motion. This simple 3D animation allows users to rotate the view to see exactly that. Right click and drag to rotate the view. If you are using a mobile device, use two fingers to drag.
