&
CURRICULUM & LITERACY The Physical World
Potato cannons pendulums At a Wellington secondary school one science teacher is fostering a love for physics among his students through a myriad of hands-on experiments, writes MELISSA WASTNEY.
E
arlier this year, the PPTA released a series of video clips about the value of New Zealand teachers, featuring vignettes of everyday teachers doing their thing. Featured in one of these clips is a long metal tube firing a potato high into the air, as uniformed schoolboys watch and whoop. Welcome to Doug Walker’s physics class at St Patrick’s College in Kilbirnie, Wellington. Spurred on by this video, I visited his year 13 physics class, notebook in hand, to see the vegetable cannon in action. (Doug has made a video clip explaining how he built his air rocket launcher, or giant spud gun. Watch it here: bit.ly/1jMqvro)
Getting the balance right
Doug says he tries to strike a balance in his physics class between practical work and writing and recording, so that about 50 per cent of the class is spent doing hands-on science. He believes that once students have the conditions for conducting experiments and are playing with equipment, they will come up with innovative ideas of their own. “I’ve found fifty-fifty is a good balance and keeps the students motivated,” he says. “Hands-on experiments capture their interest. And I think if you can do that, the battle is won.” And it seems the students are as enthusiastic. At the suggestion of demonstrating a concept to me using oxalic acid and iron filings, one student exclaims, “That one is mint as!” When I visited the school on a sunny winter’s morning, Doug’s year 13 physics students showed me some of their favourite experiments. First on the list was the department’s own giant pendulum. This hangs at the front of the
Doug made a class Ruben’s Tube, which the students use to show me the relationship between sound waves and sound pressure. The Ruben’s Tube, consisting of a length of steel pipe with holes along the top, is sealed at both ends, but one end is attached to a small speaker that is in turn powered by a signal generator, and the other to a supply of gas. As the tube is filled with gas, the perforations are lit, and show how the sound waves affect the flames. Students demonstrating the class Ruben’s Tube. 32 >> New Zealand Science Teacher
classroom and weighs 60 Newtons. Used to demonstrate the principle of energy loss due to friction, students took turns drawing the ball close to their bodies then standing quite still as it swung away. The class has recently used a high frame rate camera to analyse the velocity and momentum of the falling ball. The pendulum has a variety of uses in the physics classroom, though ‘fun’ is its primary function, admits Doug. “In Level 1 classes, we use it to demonstrate conservation of energy, predicting speed and checking our calculations using a high frame rate recording and free software called Tracker.” In Level 2, students use the pendulum to work out physics relationships from basic principles, such as the period of a pendulum, and demonstrating that mass has no effect on this by measuring the period with and without a student sitting on it as it swings. Level 3 students extend these principles to calculate simple harmonic motion.