5.5 92 A scalar quantity is a physical quantity that has only magnitude (size) but no direction. Scalars are fully described by a numerical value and a unit. A vector quantity is a physical quantity that has both magnitude (size) and direction. SPEED SPEED VS VELOCITY Speed and velocity are kinematic quantities: they describe motion without considering the forces that cause it. They focus only on how an object moves (distance, displacement, time, and direction) rather than why it moves. Speed Speed is a scalar quantity that refers to how fast an object is moving regardless of direction. It is defined as the rate at which an object covers distance per unit of time. A fast-moving object has a high speed and covers a relatively large distance in a short amount of time. On the other hand, a slow-moving object covers a relatively small amount of distance in the same amount of time. An object with no movement at all has zero speed. The standard unit of speed is metres per second (m/s), but it can also be measured in kilometres per hour (km/h) or miles per hour (mph). The formula for speed is: distance Speed = time displacement: spostamento to point: indicare 172 SCIENCE AND PHYSICS Power and speed be hands and feet. Ralph Waldo Emerson Velocity Velocity is a vector quantity that refers to the rate at which an object changes its position. Imagine a person moving rapidly one step forward and one step back always returning to the original starting position: it would result in zero velocity. Since the person always returns to the original position, the motion would never result in a change in position. If a person in motion wants to maximise their velocity, then that person should try their best to move as far as possible from their original position, in other words every step must move that person further from where they started. An object s velocity points in the same direction as its movement. It would not matter whether the object is speeding up or slowing down. If an object is moving rightwards, then its velocity is described as being rightwards. If an object is moving downwards, then its velocity is described as being downwards. In order to calculate velocity, we need to know the displacement ( x), i.e. the straight-line distance from the initial to the final position, including direction. The standard unit for velocity is metres per second (m/s). The formula is: displacement ( x) Velocity = ------------------------ time Acceleration Acceleration refers to the rate at which velocity changes with time, in terms of speed, direction, or both. It is a vector quantity and its standard unit is metres per second squared (m/s²). The formula is: v Aceleration: Vt SPEED VELOCITY ACCELERATION