2 Birchbark canoe Travois Light aircraft York boat Chariot Litter Trading ships Motor car Barge Windjammer Steam train Covered wagon Penny farthing Phaeton Gondola Trireme Montgolfier balloon Paddle boat 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 Contents sail shape steam engine Center OF GRAVITY SPOKED WHEEL SPRINGS STREAMLINING KNOTS EXPANDING AIR PADDLE wheel WOOD BARK FRICTION PROPELLERS KINETIC ENERGY wheel and axle gravity RUDDER combustion engine locks ACTION
40 42 44 Horse bus horsepower Coracle UPTHRUST Glossary 46 Index 48 Credits We have come a long way since the invention of the wheel although many forms of transport still rely on its use However nowadays we expect to move from place to place at speed and in comfort To do work machines need energy The energy that machines use may be electrical energy or chemical energy from fossil fuels such as gasoline or diesel Power is the rate at which work is done It is measured in watts or horsepower Power can be as little as the power from a sedan chair porter’s arms or as much as the water power turning the wheel of a paddle boat Let’s look at some old machines that paved the way for the exciting inventions of today and the science that made it possible 3
Windjammer ACTION 4What helps drive a windjammer forward at speed
Imagine the force of the wind as it was stopped or jammed by the huge sails of the merchant ship a ship that sped over the ocean carrying its cargo from land to land This is where these great ships got their name windjammer These three to five-masted ships were heavy vessels with hulls or frames made of steel Designed to carry heavy cargo over long distances they relied on the wind power caught in up to 20 large square canvas sails to drive them forward Although popular in the late 1800s these mighty ships were still in use in the 1950s And there are even plans to bring them back into use After all wind is a cheap and environmentally safe form of power even if an engine might be needed for those calm days at sea ANSWER SAIL SHAPE It’s the shape of the windjammer’s sail that helps drive the craft forward The sail is curved with a slight bulge in the middle This means that the side on the outside of the curve is slightly longer than the side on the inside The wind moving along the longer side has to travel faster to meet up with the wind moving along the short side Faster-moving air means less pressure or push Slower-moving air means more pressure So the slower-moving air on the inside of the sail has more pressure and pushes the sail forward The 6-masted Preussen was the largest windjammer ever built wind slower moving air higher pressure push forward 5
