An object cannot have zero speed and a non-zero velocity simultaneously, as velocity includes speed as part of its definition. Speed is a scalar quantity representing how fast an object is moving, while velocity is a vector quantity, including both speed and direction. If an object's speed is zero, it means the object is not moving. Consequently, its velocity is also zero since velocity cannot exist without movement. For example, if a car is stationary at a traffic light, its speed is zero. Therefore, its velocity is also zero, regardless of the car's orientation or the direction it is facing. This distinction is crucial in understanding motion, as it helps differentiate between the mere presence of speed and the specific directional movement characterised by velocity.

Air resistance significantly affects the velocity of a falling object. When an object falls, it accelerates due to gravity, increasing its speed and, consequently, its velocity. However, as the object's speed increases, so does the air resistance it encounters. This resistance acts in the opposite direction to the object's motion, reducing its acceleration. Eventually, the object reaches a point where the downward force of gravity is balanced by the upward force of air resistance. At this stage, called terminal velocity, the object stops accelerating and continues to fall at a constant speed. The effect of air resistance and the concept of terminal velocity are critical in fields like aerodynamics and parachuting, where controlling the descent speed is essential. The shape, size, and mass of the object, along with the density of the air, determine how quickly it reaches its terminal velocity.

Distinguishing between instantaneous speed and average speed is vital in practical scenarios for accuracy and relevance. Instantaneous speed refers to the speed of an object at a particular moment, like the reading on a car's speedometer. It is crucial for tasks requiring precise speed measurements at specific times, such as enforcing speed limits or in sports timing. On the other hand, average speed is the total distance travelled divided by the total time taken. This is useful for planning journeys, estimating travel times, and understanding the efficiency of a trip. In real-world applications, relying solely on instantaneous speed might not give a true representation of a journey's overall pace, whereas using only average speed might overlook critical variations in speed that occur during the trip. For instance, a car might have an average speed of 60 km/h on a journey, but knowing its instantaneous speeds is essential for understanding if it exceeded the speed limit at any point.

Relative speed is a crucial concept in understanding how two objects in motion perceive each other's speed. When two objects are moving in the same direction, their relative speed is the difference in their individual speeds. For example, if one car is moving at 50 km/h and another at 70 km/h in the same direction, the relative speed from the perspective of the slower car is 20 km/h. Conversely, if the objects are moving in opposite directions, their relative speeds are added. So, if the same cars were moving towards each other, their relative speed would be 120 km/h (50 km/h + 70 km/h). This concept is essential in collision avoidance systems in vehicles, where the relative speed determines the time and distance needed to avoid a collision. In the world of physics, understanding relative speed helps us comprehend how objects interact with each other in motion, especially in scenarios involving vehicles or celestial bodies.

Distance-time graphs are instrumental in visualising and understanding the concepts of speed and velocity. These graphs plot distance on the vertical axis against time on the horizontal axis. The slope of the line on a distance-time graph represents the speed of the object. A steeper slope indicates a higher speed, while a flatter slope indicates a lower speed. If the line is horizontal, the object is stationary

(stationary). Furthermore, the shape of the line provides insights into the nature of the object's motion. For example, a straight, diagonal line indicates constant speed, whereas a curved line suggests changing speed. However, these graphs do not directly convey velocity as they do not include directional information. To analyse velocity, one needs to consider the direction of the object's movement in addition to the information provided by the distance-time graph. This is typically done by including additional data or using specific conventions, like indicating direction with arrows or using separate graphs for different directions. Thus, while distance-time graphs are excellent for analysing speed and aspects of motion, they need to be complemented with directional data to fully understand velocity.