forces and motion at work Rourke publishing Shirley Duke www rourkepublishing com
CHAPTER ONE Unseen Forces Climb aboard a roller coaster and hang on It jerks and rattles to the top of a slope It hovers a second before plunging into a stomach thrilling drop The turns sling riders from side to side A jolting stop forces everyone backward The ride is over The thrill of a roller coaster ride comes from the different forces acting on your body as the coaster changes directions and its velocity or the speed it is moving 4
All these motions are forces Forces are actions that start stop or change the shape or motion of a body Early scientists called natural philosophers noticed patterns of motion between the Sun and Moon and the changing seasons They asked questions and tried to explain their world Galileo studied motion in the late 1500s He dropped objects of different weights from a building He discovered that objects fall at the same rate Until then people believed heavy things fell faster than light ones Galileo’s discovery energized and upset scientific and religious communities F ma F ma Force Mass x Acceleration F resultant force measured in newtons N m mass measured in kilograms kg a acceleration measured in meters per second m s2 5
