Question

Julie finds a snail on the sidewalk and wants to know whether or not the snail moves throughout the day. She places a single mark on the sidewalk next to the snail.

What will Julie use the mark for initially?

determining how fast the snail moves
acting as a standard unit of measure
determining the displacement of the snail
acting as a reference point for detecting motion

Answer 1

acting as a reference point for detecting motion

The mark gives a fixed point to compare the snail's position against so Julie can tell whether and how far it moves.