Where Is It Measured From?
Before you can describe motion, answer this.
Position is the distance and direction of an object from a chosen reference point, at a given instant.
↳ Fix a reference point first; nothing else can be stated without one.
📚 Chapter Learning Kit
Describing Motion Around Us · Class 9 Science
English 5 topics 264 leveled MCQs 110 flashcards 4 games Free
Shared by a Veda teacher · Generated with Veda AI · Oct 2026
⚡ Veda Bites
💡 Key Idea
📖 Definition
💡 Key Idea
📖 Definition
📖 Definition
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The whole idea, one bite at a time
Veda Bites are swipeable micro-lessons — each one teaches exactly one idea. Here's a taste from this kit; the app has the full deck.
Motion and Rest
When is something moving?
↳ Both are stated relative to the reference point, never absolutely.
Plus and Minus on a Line
Two directions, two signs.
On a straight line only forward and backward are available, so directions are written as plus and minus signs.
↳ One signed number carries both how far and which way.
Average Speed
How fast is it going?
Distance carries no direction, so neither does speed. A number with units says it all.
↳ Built from the path covered, so it inherits no direction.
Average Velocity
How fast, and which way?
Its direction matches the displacement, shown by a plus or minus sign on a line.
↳ Built from displacement, so it inherits displacement's direction.
Speed Against Velocity
Same units, different quantities.
↳ You cannot tell them apart by units - only by what sits on top of the fraction.
📖 Smart notes
What you'll study, topic by topic
1
Position, Distance and Displacement
Describing motion begins with fixing a reference point and stating both how far an object is and in which direction. From there, distance travelled and displacement separate cleanly: one counts the whole path, the other…
- To say where something is, you must first fix a reference point, because a position is given by the distance and the direction of the object…
- An object counts as being in motion when its position relative to the reference point changes as time passes, and as being at rest when that…
- For an object confined to a straight line only two directions are available, forward and backward, and these are written with plus and minus…
~30 min · full explanation, examples & memory tricks in the app
2
Speed, Velocity and Acceleration
Average speed divides the path covered by the time taken and carries no direction. Average velocity divides displacement by time and does carry one. Average acceleration measures how fast velocity itself changes, and poi…
- Average speed tells how fast an object moves and is found by dividing the total distance travelled by the time interval over which that dist…
- Because distance travelled carries no direction, average speed calculated from it carries none either, and is described by a numerical value…
- An object covering equal distances in equal intervals of time, for every choice of interval, is in uniform motion in a straight line and mov…
~40 min · full explanation, examples & memory tricks in the app
3
Position-Time Graphs
A position-time graph shows where an object was at every instant, and its shape gives away the motion: a straight line means constant velocity, a curve means acceleration, and a line parallel to the time axis means the o…
- Representing motion as a graph gives a visual picture of how position, velocity and acceleration change with time, and it makes three jobs e…
- Every graph in this chapter describes motion in a straight line in one direction only, and in that special case the distance travelled equal…
- One consequence: with the object starting from zero position, the same drawing serves as both a position-time and a distance-time graph, and…
~35 min · full explanation, examples & memory tricks in the app
4
Velocity-Time Graphs
A velocity-time graph does two jobs at once. How steeply its line rises or falls gives the acceleration, and the area it encloses with the time axis gives the displacement, so one drawing yields both quantities without a…
- A velocity-time graph represents the change in an object's velocity with time, and it is plotted by the same steps used for a position-time…
- When the velocity of a car is constant, the line runs level with the X-axis and the acceleration works out at zero, as for a car holding 72…
- A line climbing steadily shows velocity increasing by equal amounts in equal intervals of time, so the acceleration is constant and points t…
~40 min · full explanation, examples & memory tricks in the app
5
Kinematic Equations and Uniform Circular Motion
Three equations tie together displacement, time, the two velocities and the acceleration, so that any two unknowns can be found from the rest. Then the chapter leaves the straight line altogether: an object circling at u…
- When the acceleration stays constant, its value at every instant matches the average acceleration taken over any interval, which is what mak…
- Rearranging the definition of average acceleration gives the first equation, $v = u + at$, which yields the velocity at any time once the st…
- The second comes from the area under a velocity-time line whose starting value is not zero: a rectangle plus a triangle, which works out to…
~45 min · full explanation, examples & memory tricks in the app
❓ Leveled MCQ practice
Try the smart MCQs from this kit
264 questions laddered from warm-up to topper-level, each with an explanation. A taste:
Which of these must be fixed before a position can be described?
Beginner
A A time interval
B A velocity
C An acceleration
D A reference point
Show answer & explanation
A reference point
Position means distance and direction measured from somewhere.
An object is said to be at rest when:
Beginner
A it has no mass
B it is lying on the ground
C it stays exactly where it was, relative to the point being measured from, as time passes
D its displacement equals the distance it travelled
Show answer & explanation
it stays exactly where it was, relative to the point being measured from, as time passes
Rest and motion are both defined relative to a reference point.
The SI unit of displacement is the:
Beginner
A second
B kilogram
C metre
D newton
Show answer & explanation
metre
Total distance travelled is measured in the same unit.
A single reading of a clock at a given moment is called:
Beginner
A an instant of time
B a time interval
C a duration
D a period
Show answer & explanation
an instant of time
The stretch between two such readings is the time interval.
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