Sagot :
Answer:
- An object is in motion if it changes position relative to a reference point. Objects that are fixed relative to Earth – such as a building, a tree, or a sign - make good reference points.
Answer:
It's possible that the way in which these terms are used varies from person to person, even among professionals in the field. However, in the usage I'm familiar with, displacement is the change in position, period. Definition #2 is correct and #1 is wrong. (The length and direction of a line from a fixed reference point is just called position.)
In this usage the proper form of the constant acceleration kinematic equation would be Δx⃗ =v⃗ t+12a⃗ t2, or x⃗ =x⃗ 0+v⃗ t+12a⃗ t2, where x⃗ is position and v⃗ is initial velocity. It would be valid to write x⃗ =v⃗ t+12a⃗ t2 if you always choose the origin to be at the initial position, but that seems like an unnecessary restriction.
Alternatively, you could write the equation in terms of displacement. If you use s⃗ for displacement, the equation would be s⃗ =v⃗ t+12a⃗ t2. That is because s⃗ =Δx⃗ (displacement equals change in position). If these textbooks you're using are using this notation in which s⃗ is displacement, then it seems very strange to write v⃗ =Δs⃗ /Δt. That is unconventional and probably unclear notation, although it might not necessarily be wrong.
Explanation:
What is the "official" or most useful definition of displacement in the context of kinematics? There are two common ones:
Displacement is the length and direction of a line from a fixed reference point. (Basically position).
Displacement is the change in position.
Textbooks using the first definition frequently define velocity as v=Δs/Δt (where s is displacement) but then for acceleration give equations such as s=ut+1/2at2 (if they were consistent, they would have to use Δs). What throws me off is that are the better textbooks.
: A displacement vector is the straight path between the initial and the final position. But velocity is defined as v=Δd/Δt.
What is the "official" or most useful definition of displacement in the context of kinematics? There are two common ones:
Displacement is the length and direction of a line from a fixed reference point. (Basically position).
Displacement is the change in position.
Textbooks using the first definition frequently define velocity as v=Δs/Δt (where s is displacement) but then for acceleration give equations such as s=ut+1/2at2 (if they were consistent, they would have to use Δs). What throws me off is that are the better textbooks.
A displacement vector is the straight path between the initial and the final position. But velocity is defined as v=Δd/Δt.