Science Common Sense

1656 - Why is the relative velocity of two point masses moving on the same line the difference of their velocities?

Imagine you and your friend are walking in the same direction on a straight road. You're moving at 5 km/h, and your friend is moving at 3 km/h.

To find the relative velocity, think about how fast you're moving away from or catching up to your friend. Since you're both moving in the same direction, you'll subtract your speeds.

Relative velocity = Your speed - Friend's speed Relative velocity = 5 km/h - 3 km/h Relative velocity = 2 km/h

This means you're 2 km/h faster than your friend.

Now, imagine if your friend was moving in the opposite direction at 3 km/h. To find the relative velocity, you would add your speeds.

Relative velocity = Your speed + Friend's speed Relative velocity = 5 km/h + 3 km/h Relative velocity = 8 km/h

This means you're 8 km/h faster, relative to your friend.

So, when two point masses are moving on the same line in the same direction, you subtract their velocities, and when they're moving in opposite directions, you add their velocities.