Question

Bacteria move back and forth by using their flagella (structures that look like little tails). Speeds of up to 50 µm/s (50×10^-6 m/s) have been observed. The total distance travelled by a bacterium is large for its size, while its displacement is small. Why is this?

Short answer

Bacteria move back and forth, and the difference between their original and end locations will be minimal, resulting in a modest displacement.

Step-by-step solution

Distance and Displacement

To describe an object's motion, you must first be able to define its location or where it is at any given time. You'll need to indicate its location in relation to a useful reference frame.

The location of an item changes as it moves with respect to a reference frame (for example, when a lecturer walks to the right of a whiteboard or when a passenger travels toward the back of an airliner). Displacement is the term for this shift in position. The term "displacement" refers to the movement or displacement of an object.

Movement of bacteria

In the case of bacteria, it moves back and forth, so the total distance travelled by the bacteria will be the sum of all the lengths covered by the bacteria.

But the displacement will be the measurement of the shortest distance between the initial and the final position.

As the bacteria is moving too and coming back, the displacement covered by the bacteria will be less.

Motion of bacteria

Hence, here in this figure, the distance is all the length along the zigzag line, whereas displacement is only the shortest distance, so it is less.