(i) When a body travels in straight line path, its distance and displacements are equal and hence in a given time, velocity is equal to speed. (ii) Average velocity of a body may be equal to zero if the total displacement of is body is equal to zero, but average speed will not be equal to zero unless and until distance covered is zero (i.e., body at rest). (iii) To describe the velocity, direction is necessary as velocity is speed in a specific direction.

Imagine you're on a hike, following a trail that turns and winds through the mountains. The distance you cover is like the total length of the trail you've hiked, including every twist and turn. On the other hand, displacement is a straight shot from your starting point to your endpoint, regardless of the path you took. In physics for class 7 students, we deal with these concepts to understand motion.

When motion occurs in a straight line, it's like taking a shortcut that doesn't turn or deviate; your distance and displacement are the same, as there's no difference between the path taken and the direct line from start to finish. This is crucial because it simplifies the calculations for speed and velocity, two concepts closely linked to distance and displacement.

Speed is how fast you're going without worrying about your destination—think of it like the number you see on a speedometer in a car. Now, if you add your destination to the mix, saying, 'I’m heading north at this speed,' you're talking about velocity. It's speed with a direction. Both are important when studying physics motion concepts in class 7.

Comparing Speed and Velocity

Speed is a scalar quantity—it has just the magnitude, like '60 mph.' Velocity, however, is a vector quantity—it has both magnitude and direction, like '60 mph north.' Knowing the velocity is more informative because it tells us the speed an object is moving and in which direction.

Let's say you're watching a one-hour movie at the cinema. If you get up and walk around but end up back in your seat by the end of the movie, your average velocity is zero because you haven't changed your position from start to finish. But your average speed is not zero because you indeed moved around—this is the total distance you walked divided by the movie's duration.

Average speed and velocity are like summaries of your entire trip. Average speed is straightforward—it's how fast you've been moving on average. Average velocity adds more context by considering your overall change in position. If you start and end in the same place, like returning to your seat, average velocity says, 'You haven't gone anywhere on average,' even though you moved around.

Scalar quantities are the simple numbers in physics; they tell you 'how much' but not 'which way.' Examples include mass, speed, and distance. They're like the money in your wallet—you know the amount, but it doesn't tell you where you're going to spend it.

In contrast, vector quantities give you more information—they have both a magnitude and a direction, like an arrow. Think of it as giving you money and a shopping list; it tells you 'how much' and 'where to go.' This would include quantities such as velocity, displacement, and force. Understanding the difference between these two types of quantities is essential as they tell us different things about movement and can change the meaning of a physics problem entirely.