The document discusses key concepts in motion including point of reference, trajectory, distance, displacement, and the differences between distance and displacement. It notes that in Newtonian physics, all motion must be defined relative to a point of reference. Distance refers to the length between two points, while displacement considers both length and direction from an initial to final position. An object's distance traveled and displacement can differ, such as when running multiple laps around a track.

2. Point of reference
• Observational point tied to the motion of an
observer.
• In Newtonian physics, all motion must be
defined in terms of a point of reference.
• Relative Motion

3. Point of reference
• Is the speed of the ball different relative to the
pitcher, the truck driver, and the jet pilot? Why or
why not?

4. Point of reference
• Trajectory: The path of a moving body.

5. Distance
• Distance is the measurement from one point
to another. The length of the trajectory
• Distance may refer to a physical length, a
period of time, or an estimation.

6. Displacement
• Displacement ( x) – difference between an object’s final
position and its starting position.
– Does depend on direction.
• Displacement = final position – initial position
• x = xfinal – xinitial
• In order to define displacement, we need directions.
• Examples of directions:
– + and –
– N, S, E, W
– Angles

7. Displacement vs. Distance
• Example of distance:
– The ant walked 3 cm.
• Example of displacement:
– The ant walked 3 cm EAST.
• An object’s distance traveled and its
displacement aren’t always the same!

8. Displacement vs. Distance
• An athlete runs around a track that is 100 meters long
three times, then stops.
– What is the athlete’s distance and displacement?
• Distance = 300 m
• Displacement = 0 m
• Why?

9. Displacement and distance
To go to school from home... your
home
Size = length of
this arrow
your displacement from
school home to school
A displacement has size & direction.

10. Displacement and distance
To go to school from home... your
home
l2 l1
l3
your
school Distance = length of path you
travelled = l1 + l2 + l3
( size of displacement)