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Average speed is a key concept in understanding motion. It reflects how fast an object moves, disregarding direction. To grasp this, consider Edith's relay race run. In total, she travels 50.0 meters — 25.0 meters out and then 25.0 meters back. The average speed is determined by dividing this total distance by the total time taken for the journey. In Edith's case, she spends 20 seconds on her outward trip and 15 seconds returning, totaling 35 seconds. Hence, her average speed can be calculated as follows:

• Total distance: 50.0 m
• Total time: 35.0 s

The formula for average speed is:\[\text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{50.0 \text{ m}}{35.0 \text{ s}} = 1.43 \text{ m/s}\]Average speed is always a positive number as it doesn't involve direction, just total distance and time.

When discussing motion, 'displacement' points to the change in position of an object. It's a vector quantity, which means it has both a magnitude and a direction. This is different from 'distance,' which only measures the path traveled, not the direction. In the relay race scenario, Edith's displacement for each segment: the initial 25.0 m and the 25.0 m return trip, is straightforward. Initially, her displacement is exactly 25.0 m towards her target. However, when she completes the round trip by returning to the starting point, the net displacement becomes zero. Displacement focuses on the change in position from the initial to the final point, which can be given as:

• Initial displacement for the first 25.0 m: 25.0 m
• Displacement returning to start: -25.0 m
• Total displacement for round trip: 0 m

Displacement can sometimes be tricky, especially when motion involves backtracking to the starting point.

Kinematics is the branch of physics describing the motion of objects without considering the forces causing them. It provides the tools to describe motion through concepts like velocity, speed, and displacement. In Edith's race, the kinematics principles help determine specifics like her average velocities and speeds at different parts of her run. Her motion can be quantified by:

• Velocity, which incorporates both speed and direction, making it a vector.
• Speed, which is scalar, representing only how fast she's moving regardless of direction.

Kinematics involves examining Edith's average velocities. For instance, running the first 25.0 m at 1.25 m/s and the returning 25.0 m at 1.67 m/s reflects the application of kinematics concepts, giving clear insights into the nature of her motion.

Calculating motion for a round trip involves special attention since the starting and ending points are the same. In such scenarios, one might compute both average speed and average velocity.For Edith's round trip in the relay:

• The total distance covered is 50.0 m, considering her 25.0 m outbound and 25.0 m return leg.
• Average velocity differs here because her starting and ending points are the same, which makes the displacement zero.

Displacement being zero impacts the average velocity calculation, since:\[\text{Average velocity} = \frac{\text{Total displacement}}{\text{Total time}} = \frac{0 \text{ m}}{35.0 \text{ s}} = 0 \text{ m/s}\]In contrast, the average speed considers only the total distance and time, giving a clearer perspective on Edith's progress throughout her race.