Speed, distance, and time

Speed, distance, and time

Fundamental Concepts

  • Speed is a measure of how quickly an object moves.
  • Distance represents how far an object moves.
  • Time signifies the duration over which the object moves.

Basic Formula

  • The primary way to explore the relationship between these three quantities is via the formula speed = distance/time
  • In real life applications, units of speed could be kilometres per hour (km/h), metres per second (m/s), or miles per hour (mph).

Manipulating the Formula

  • If the speed and time are known, you can find the distance travelled with distance = speed × time.
  • If the distance travelled and the speed are known, you can calculate the time taken with time = distance/speed.

Important Conversions

  • Remember to convert time units with these rules:
    • 60 seconds = 1 minute (min)
    • 60 minutes = 1 hour (h)
  • Similarly, to convert distances keep in mind:
    • 1 kilometre = 1000 metres (m)
    • 1 mile = 1.60934 kilometres (km)

Graphing

  • Graphically, distance can be represented on the y-axis, with time on the x-axis. If an object’s speed is constant, this will create a straight line on a graph.
  • The gradient of the line on a distance-time graph represents the speed of the object.

Relative Speed

  • When two objects are moving in the same direction, their relative speed is the difference of their individual speeds.
  • When two objects are moving toward each other, their relative speed is the sum of their individual speeds.

Average Speed

  • Average speed is total distance divided by total time, and does not indicate constant speed at all points of travel.
  • It’s important to note that average speed may not be the same as the speed the object is travelling at specific points during the interval.

Distinction Between Speed and Velocity

  • While speed is a scalar quantity, representing the magnitude of movement, velocity is a vector quantity, giving both speed and direction.
  • This means that if an object changes direction, but maintains a constant speed, its velocity will have changed.

Acceleration

  • Acceleration is the rate of change of velocity. If an object changes its speed, it is said to be accelerating.

  • The formula for acceleration is acceleration = change in speed/time. This is expressed in units such as metres per second squared (m/s^2) or kilometres per hour squared (km/h^2).

  • The gradient of the line on a speed-time graph represents the acceleration of the object. If this line is horizontal, acceleration is zero and speed is constant.

Deceleration

  • Deceleration is negative acceleration - it occurs when an object slows down.
  • A falling object, for example, will decelerate as it comes to a stop.