# Teaching Resources

Physics teaching resources

## 3D Virtual Experiment on Torsional Pendulum

In preparation for HBL in 2022, I designed a simple virtual experiment that will allow for students to collect data on oscillations using their own stopwatches and investigate the relationship between the period of oscillation and two separate variables. To access the simulation on GeoGebra, visit https://www.geogebra.org/m/jhc4xvpe.

Based on the given relationship $$T = cm^aL^b$$ where a, b and c are constants, students will be tasked to find the constants a, b and c. Students will then attempt to “linearise” the equation such that the independent variables m and L can be tested one by one.

Examples of data collected can be plotted using Excel to give the following graphs from which the gradients and vertical intercepts can be obtained instantly.

## Hidden Circuits Interactive

I made this interactive tool using javascript for the teaching of DC circuits for integration with SLS as part of the IP4 Physics blended learning experience in the upcoming weeks.

The intention of this interactive is for students to do a preliminary inquiry activity to exercise what they learnt about series and parallel circuits. They can be tasked to draw out what they think the circuit diagram will be like, either on Nearpod or SLS.

Students can even notice the differences in brightness under different conditions. Questions can be designed around this as well.

Previously we used to construct little boxes with wires hidden underneath. However, due to wear and tear and with Covid-19’s safe management measures, a digital version that can be accessed via the students’ mobile devices is more suitable.

Light bulb image is adapted from Good Ware from www.flaticon.com
Switch image is adapted from Those Icons from www.flaticon.com

## Pendulum-Powered Car

This pendulum-powered car is constructed using Lego Technic parts. I used mainly Lego beams to create the chassis and an “A” frame from which the pendulum is suspended. The pendulum is made of Lego beams and some wheels.

When the pendulum swings, it experiences an acceleration towards its equilibrium position. By the principle of conservation of momentum, the car experiences a change in momentum in the opposite direction. Since the acceleration of the pendulum changes its direction every half a cycle of its oscillation, the car will only oscillate about its original position if the wheels of the car are free to turn throughout the oscillation.

A escapement mechanism which consists of a beam resting on a pair of 40-tooth gears attached to the front wheels prevent the wheels from rotating in the opposite direction. This means that the car will only be moving forward during the half of the pendulum’s oscillation when its displacement is at the front of its equilibrium position and pauses during the other half.

## Tensegrity Explained

There is a new internet trend called “tensegrity” – an amalgamation of the words tension and integrity. It is basically a trend of videos showing how objects appear to float above a structure while experiencing tensions that appear to pull parts of the floating object downwards.

In the diagram below, the red vectors show the tensions acting on the “floating” object while the green vector shows the weight of the object.

The main force that makes this possible is the upward tension (shown below) exerted by the string from which the lowest point of the object is suspended. The other tensions are downward and serve to balance the moment created by the weight of the object. The centre of gravity of the “floating” structure lies just in front of the supporting string, where the green vector representing its weight is in the following image. The two smaller downward vectors at the back due to the strings balance the moment due to the weight, and give the structure stability sideways.

This is a fun demonstration to teach the principle of moments, and concepts of equilibrium.

These tensegrity structures are very easy to build if you understand the physics behind them. Some tips on building such structures:

1. Make the two strings exerting the downward tensions are easy to adjust by using technic pins to stick them into bricks with holes. You can simply pull to release more string in order to achieve the right balance.
2. The two strings should be sufficiently far apart to prevent the floating structure from tilting too easily to the side.
3. The centre of gravity of the floating structure must be in front of the string exerting the upward tension.
4. The base must be wide enough to provide some stability so that the whole structure does not topple.

Here’s another tensegrity structure that I built: this time, with a Lego construction theme.

## Template for Creating GeoGebra Animations

In an introductory sharing for the use of GeoGebra to my colleagues, I have prepared a simple template for them to try their hands at animations of points and other elements.

You can try the same too. Create a moving point by typing into the Input field (5,5*sin(time)) so that you get a point at x = 5 that oscillates between 5 and -5 in the vertical direction.

## Relationship between displacement-time and velocity-time graphs

Through this GeoGebra app, students can observe how the gradient of the displacement-time graph gives the instantaneous velocity and how the area under the velocity-time graph gives the change in displacement.

In the GeoGebra app below, you will see a displacement-time graph on the left and its corresponding velocity-time graph on the right. These graphs will be referring to the same motion occuring in a straight line. Instructions

1. Click “Play” and observe the values of displacement and velocity change in each graph over time.
2. Note the relationship between the gradient in the displacement-time graph and the value of velocity.
3. Note the relationship between the area under the velocity-time graph and the value of displacement.