SCIENCE
which is a long tail cargo bike. It can carry up to 100kg (in theory!), but in turn weighs quite a bit to support all that. I've often felt like a tortoise, making my way slowly up a hill, with my âhouseâ on the back. Pedalling yourself and all your gear up a hill obviously requires energy input â first to get things moving (the first law of motion! An object at rest will stay that way, unless a force acts upon it), and then to overcome the force of gravity. The work you put into raising yourself and the bike up a hill gets turned into gravitational potential energy. It can be a real struggle creaking up to the top (Wellington is an ideal training ground), but all that stored energy has a wonderful flipside. Your gravitational potential is turned into kinetic energy, and a fully loaded bike can really move! With only friction, the wind and traffic conditions to slow you down, you can cover a lot of ground. Once you're flying down that hill, you have momentum. You are mass in motion, and momentum is that mass times the velocity. With a fully loaded touring setup, all the mass will keep you travelling for some time. I like to think that cycling over hills is only half a ride, going up, and then coasting down. Hills are fascinating, but it can be good to take your mind off the upward grind. I often find myself thinking about instantaneous rates of change â cast
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your mind back to high school calculus for this one. Between any two points on a curve (or say, a hill), we can find the average slope or tangent. We can bring these points closer together, finding a more accurate tangent â but what if we want to know the slope at one single point? For that we need differential calculus. At any centimetre along a hill, we could stop and calculate the slope. In practice, nearing the top of a hill, I do try to spot the point, at which the slope finally becomes zero, flattens out, and the hill âstopsâ Hills, gravity, hours of cycling â how come you donât just fall over sometimes? One of the reasons lies in the wheels. As they turn, the angular momentum of their spin in conserved. The wheels âwantâ to stay in the plane in which theyâre travelling, which means that your bike does a good job of staying upright all by itself. Like so many things, cycling is a whole string of little miracles. Of course, you don't need to know any of this to enjoy the ride. The big question is, where do you want to cycle today? David Klein will perform Tour de Science on 12 March, The Dowse 2:00 pm; 15 March, Space Place 7:00 pm; 18 March, Bicycle Junction 7:00 pm The New Zealand Bicycle Film Festival, Nga Taonga, from 28 March