1. Similarities
   1. Measures of how fast an object is moving: Both speed and velocity quantify how quickly an object is changing its position. They both describe the rate of motion of a body.
   2. Same Units: Speed and velocity share the same units of measurement, such as metres per second (m/s), kilometres per hour (km/h), or miles per hour (mph). For instance, 60 km/h can be used as a measure for both speed and velocity, as long as the direction is also specified for velocity.
2. Differences
   1. Definition
      1. Speed: Speed is defined as the distance an object travels per unit of time, irrespective of direction. It is a measure of how quickly an object is moving without considering its direction. For example, a car might have a speed of 60 km/h.
      2. Velocity: Velocity, on the other hand, is the rate of change of displacement with respect to time. It’s the speed of an object in a specific direction. For example, a car’s velocity could be 60 km/h due north. Velocity is a measure of how quickly an object is changing its position in a specific direction.
   2. Significance
      1. Speed: Speed provides information about the quickness of movement but does not tell us anything about the direction of that movement.
         • It’s a scalar quantity, meaning it only has a magnitude (size).
         • A car travelling at 20 m/s has a speed of 20 m/s.
      2. Velocity: Velocity provides a complete description of motion.
         • It tells us both how fast an object is moving and the direction it is moving in.
         • Velocity is a vector quantity, possessing both magnitude and direction.
         • For example, an aircraft may have a speed of 200 m/s, but a velocity of 200 m/s due north.
   3. Calculation
      1. Speed: Speed is calculated by dividing the total distance travelled by the total time taken. The formula is typically written as:
         • For example, if a car travels 400 m in 20 seconds, its speed is 400m/20s = 20 m/s.
         • Average speed is the total distance travelled divided by the total time taken.
      2. Velocity: Velocity is calculated by dividing the displacement by the time taken. Displacement is the distance an object moves in a specified direction.
         • Because displacement is a vector quantity, velocity is also a vector.
3. Additional Points
   1. Direction: The direction is critical for velocity. For example, a velocity of -280m/s means the object is moving downwards. In a straight line, you can use positive or negative signs to denote direction.
   2. Constant Speed vs. Constant Velocity: An object moving at a constant speed may still have a changing velocity if it changes direction. For example, a car moving at a constant speed around a circular track does not have constant velocity because its direction is constantly changing. Constant velocity means both the speed and the direction are constant.
   3. Vectors and Scalars: Speed is a scalar quantity; it only has magnitude. Velocity is a vector quantity; it has both magnitude and direction. Displacement, like velocity, is a vector, whereas distance is a scalar.
   4. Instantaneous Speed: Instantaneous speed is the speed at a particular moment in time. Average speed, on the other hand, is calculated over a longer time interval.
   5. Graphs:
      • On a distance-time graph, the gradient (slope) represents the speed.
      • On a speed-time graph, the gradient shows acceleration, and the area under the curve represents the distance travelled.
   6. Real World: In many real-world situations, objects rarely move at a constant speed, and thus using average speed is often necessary.