DISTANCE AND DISPLACEMENT

​Are two quantities that may seem to mean the same thing yet have distinctl different definitions and meanings.

Distance is a scalar quantity that refers to “howmuch ground an object has covered” during its motion.

​Displacement is a vector quantity that refers to “how far out of place an object is”; it is the object’s overall change in position.

​ To test your understanding of this distinction, consider the motion depicted in the diagram below. A physics teacher walks 4 meters East, 2 meters South, 4 meters West and finally 2 meters North.

​Event hough the physics teacher has walked a total distance of 12 meters, her displacement is 0 meters. During the course of her motion, she has “covered 12 meters of ground” (distance =

12 meters). Yet when she finished walking, she is not “out of place” -i.e. there is no displacement for her motion (displacement = 0 m).

Displacement, being a vector quantity must give attention to direction. The 4 meters east cancel the 4 meters west; and the 2 meters south cancels the 2 meters north. Vector quantities such as displacement are direction aware. Scalar quantities such as distance are ignorant of direction. In determining the overall distance traveled by the physics teachers, the various directions of motion can be ignored.

​Let's understand the concept of DISTANCE AND DISPLACEMENT

Concept of distance

​

​Distance here will be = 4m + 3m + 5 m = 12 m

EMM​

Displacement

If an object moves from A position to B, then the object’s position changes. This change in position of an object is known as displacement.

​

​

Displacement refers to the shortest distance between its point of origin (position A) and its point of destination (position B) no matter what path it took to get to that destination.

​

The idea that a description of motion depends on the reference frame of the observer has been known for hundreds of years. The 17^th-century astronomer Galileo Galilei was one of the first scientists to explore this idea. Galileo suggested the following thought experiment: Imagine a windowless ship moving at a constant speed and direction along a perfectly calm sea. Is there a way that a person inside the ship can determine whether the ship is moving? You can extend this thought experiment by also imagining a person standing on the shore. How can a person on the shore determine whether the ship is moving?

 Only by looking at each other can a person in the ship or a person on shore describe the motion of one relative to the other. In addition, their descriptions of motion would be identical.

​Galileo Conclusion

​

A person inside the ship would describe the person on the land as moving past the ship.

​

The person on shore would describe the ship and the person inside it as moving past.

​

  Galileo realized that observers moving at a constant speed and direction relative to each other describe motion in the same way.

​

Galileo had discovered that a description of motion is only meaningful if you specify a reference frame.

​

SCIENCE 7

​Directions: Use the diagram to determine the resulting displacement and the distance traveled by the skier during these three minutes.​

​ Distance travelled from B to C = ___________

Distance travelled from C to D = ___________

Total Distance = ______________

Displacement = ______________

SCIENCE 7

Directions: What is the coach’s esulting displacement and distance travel?

SCIENCE 7

Distance from B to C = ______________   

Distance from C to D = _________________

Distance from B to D = ______________   

Displacement = _______________________

SCIENCE 7

​

References:

1. http://www.physicsclassroom.com/class/1DKin/Lesson-1/Distance-and-Displacement

2.https://byjus.com/physics/distance-and-displacement/

3. https://openstax.org/books/physics/pages/2-1-relative-motion-distance-and-displacement