Work and energy
In physics mechanical work is done if a force acts on a body and the body moves in the direction of that force. Work equals the product of the force and the distance moved in the direction of the force: A = F · s. The unit of work is the joule (J), 1 J = 1 N · 1 m = 1 N·m: when a force of 1 N moves a body 1 m in the direction of the force, 1 J of work is done. The joule is named after the English physicist James Joule (1818–1889); 1 kJ = 1000 J. If a force acts but the body does not move (pushing a wall), or the body moves perpendicular to the force, the mechanical work is zero. A body that can do work is said to have energy. Energy is also measured in joules: the more work a body can do, the greater its energy. When work is done, the energy of one body decreases and that of another increases — energy is transferred or changes form.
“Is there work?”: pupils answer whether work is done in situations (lifting a book, pushing a wall, carrying a bag along a street, rolling a ball) and say why. Safety: do not lift heavy objects; use light books only.