Motion and rest
A kabaddi player on the mat, a rolling ball, a parked bike and a sleeping dog. Some of these keep changing their place and some do not. Looking at the position tells us whether something is moving.
When the position of an object keeps changing, it is in motion (गतीत). When its position does not change, it is at rest (स्थिर).
In the figure : In the figure the ball P stays at the same distance from the red post, so it is at rest. The ball Q keeps changing its distance from the post, so it is in motion.
Rule 1: Motion and rest — In cricket the ball is at rest in the bowler's hand, in motion when bowled, in a new direction when the bat hits it, and again at rest in the wicket keeper's hands.
- Easy : A parked cycle is at rest.
- Medium : A cycle being ridden changes position, so it is in motion.
- Exam-type : The ball goes from rest (hand) → motion (flight) → rest (catch): an object can change its state.
Rule 2: How to decide — Check whether the object's distance from a steady post changes with time.
- Easy : Distance does not change → at rest.
- Medium : Distance keeps changing → in motion.
- Exam-type : A ball rolling away from you changes its distance: it is in motion.
Motion = position keeps changing. Rest = position stays the same.
Thinking an object that moves for a moment is always in motion. It can come to rest again.
Memory clue: Position Changes = Moves.
Spot the difference
| Point | Motion | Rest |
|---|---|---|
| Position | Keeps changing | Does not change |
| Example | Moving ball | Ball in the hand |
Practice questions
- 1When is an object in motion?
- 2When is an object at rest?
- 3Give an example of an object at rest.
- 4Give an example of an object in motion.
- 5In the figure, ball P stays at the same distance from the post. Is it in motion?
- 6When is a cricket ball at rest?
- 7A boy rolls a marble; it stops after some time. Describe its state in the beginning, middle and end.
- 8Sachin says the ball is in motion all the time in a cricket game. Correct him.
Show answers (try them yourself first)
- 1When its position keeps changing.
- 2When its position does not change.
- 3A parked cycle.
- 4A bowled cricket ball.
- 5No, it is at rest.
- 6When it is in the bowler's or the wicket keeper's hand.
- 7Beginning: at rest in the hand; middle: in motion; end: at rest.
- 8The ball is at rest when it is in a hand.
Reference point
Sitting in a bus, your bag at your feet seems to be still. But a boy standing on the road sees the bag racing past. Trees by the road seem to run backwards. The answer depends on who is looking from where.
A reference point (संदर्भबिंदू) is a steady object or fixed position with respect to which we decide whether another object is in motion.
Rule 1: Motion depends on the observer — One person may see an object moving while another sees it steady. So we observe with respect to a steady object. Trees and poles seem at rest, yet the earth itself rotates on its axis and revolves around the sun.
- Easy : For you in the bus, the bag at your feet is steady.
- Medium : For a boy on the road, the same bag is moving with the bus.
- Exam-type : In a train, the next train seems to move backward if it is slower than yours, though both go forward.
In the figure : In the figure the tree on the bank is the reference point. With respect to the tree the boat changes its place, so it is in motion; for the girl sitting in the boat, the boat is at rest.
Rule 2: Using a reference point — With the right reference point we can say both whether an object moves and where it is.
- Easy : With the bus stand as reference, a shop is 200 m north.
- Medium : With the same reference, a library is 350 m south, so the distance between the shop and library is 200 + 350 = 550 m.
- Exam-type : A passenger inside a moving bus is at rest with respect to the bus but in motion with respect to the road.
In the figure : In the figure a reference point tells where an object is. With the school as the reference point, the temple is 300 m to the west and the park is 500 m to the east.
Always name the reference point when you say "moving" or "at rest".
Saying an object is at rest or in motion without saying with respect to what. Motion is relative.
Memory clue: Reference = Real fixed object to compare with.
Spot the difference
| Observer | Sees the bag as | Reference point |
|---|---|---|
| Person in the bus | At rest | The bus |
| Boy on the road | In motion | The road |
| Girl in the boat | Boat is at rest | The boat |
Practice questions
- 1What is a reference point?
- 2Why do trees seem to move backward from a moving bus?
- 3Is the bag at your feet in the bus at rest? With respect to what?
- 4What is the reference point in the boat figure?
- 5Does the earth move?
- 6In the figure the temple is 300 m west and the park 500 m east of the school. Find the distance between the temple and the park.
- 7A shop is 200 m north of the bus stand and a library is 350 m south. How far apart are they?
- 8A passenger is sitting in a moving train. Explain how he can be at rest and in motion at the same time.
Show answers (try them yourself first)
- 1A fixed object or position used to decide whether another object moves.
- 2The bus is moving; we observe them from a moving place.
- 3Yes, with respect to the bus.
- 4The tree on the bank.
- 5Yes. It rotates on its axis and revolves around the sun.
- 6300 + 500 = 800 m
- 7200 + 350 = 550 m
- 8At rest with respect to the train, in motion with respect to the station.
Linear and circular motion
A cricket ball dropped from the roof falls along a straight line. A merry-go-round at a fair carries children round and round in a circle. Two very different paths.
Linear motion (रेषीय गती) is motion along a straight line. Circular motion (वर्तुळाकार गती) is motion along a circular path.
In the figure : In the figure the car moves along a straight road, so this is linear motion. After 0, 1, 2 and 3 seconds it is at 0 m, 15 m, 30 m and 45 m.
Rule 1: Linear motion — The position changes along a straight line. A body released from a height and a fruit fallen from a tree move in linear motion.
- Easy : A fruit falls from a tree.
- Medium : A train moving along a straight track.
- Exam-type : In the car figure the car covers 15 m every second, so in 5 seconds it will be at 5 × 15 = 75 m.
In the figure : In the figure the tip of a fan blade moves along a circle round the centre of the fan: this is circular motion.
Rule 2: Circular motion — The object moves along a circular path. A slingshot and a merry-go-round move in circular motion.
- Easy : The tip of a fan blade moves in a circle.
- Medium : The hand of a clock goes round in a circle.
- Exam-type : A stone tied to a string and whirled moves in a circle.
Linear = straight line. Circular = round a centre.
Thinking a moving vehicle always shows linear motion. On a curve it moves along a curved path; its wheels also move in circles.
Memory clue: Line = Linear; Loop = Circular.
Spot the difference
| Type | Path | Example |
|---|---|---|
| Linear | Straight line | Falling fruit |
| Circular | Circle | Merry-go-round |
Practice questions
- 1What is linear motion?
- 2What is circular motion?
- 3Give one example of linear motion.
- 4Give one example of circular motion.
- 5Which motion does the tip of a fan blade show?
- 6A car is at 0 m, 15 m, 30 m after 0, 1, 2 seconds. How far will it be after 4 seconds?
- 7Classify as linear or circular: (a) a stone dropped from a hand, (b) a clock hand, (c) a ball rolling along a straight line.
- 8Rita says the wheel of a moving car shows only linear motion. Correct her.
Show answers (try them yourself first)
- 1Motion along a straight line.
- 2Motion along a circular path.
- 3A fruit falling from a tree.
- 4A merry-go-round.
- 5Circular motion
- 64 × 15 = 60 m
- 7(a) linear, (b) circular, (c) linear.
- 8The car moves in a line but the wheel also rotates in a circle about its centre.
Oscillatory and random motion
A child on a swing goes forward and back, forward and back. When a guitar string is plucked it shakes quickly to and fro. A butterfly near a flower flits here and there without any plan.
Oscillatory motion (दोलन गती) is continuous to-and-fro motion along the same path. Random motion (यादृच्छिक गती) is motion in different directions with no fixed path.
In the figure : In the figure the ball goes to and fro between A and B along the same path and passes the middle position O: this is oscillatory motion.
Rule 1: Oscillatory motion — The object moves up and down or back and forth on the same path. A swing, and the strings of a sitar, tambora or veena when plucked, move this way. A thin metal strip pushed gently down keeps vibrating for some time.
- Easy : A swing moves to and fro.
- Medium : A plucked sitar string vibrates.
- Exam-type : A pendulum of a wall clock swings between A and B, passing the middle O each time.
In the figure : In the figure the fly changes its direction again and again and follows no fixed path: this is random motion.
Rule 2: Random motion — Butterflies flying around flowers move in a zigzag way, in different directions; their motion is neither straight nor circular. Ants driven away with salt water run in all directions.
- Easy : A fly in a room moves randomly.
- Medium : Ants scattered by salt water run in all directions.
- Exam-type : Children playing tag run in many directions at the same time.
Oscillatory and random motion
In the app you can move this figure with your finger.
Open in the appOscillatory: same path, to and fro. Random: no fixed path.
Confusing oscillatory with random. Oscillation repeats along the same path; random does not.
Memory clue: Oscillate = Over and over on the Same path.
Spot the difference
| Type | Path | Example |
|---|---|---|
| Oscillatory | To and fro on the same path | Swing, sitar string |
| Random | Changing directions, no fixed path | Butterfly, ants |
| Linear (compare) | Straight line | Falling fruit |
Practice questions
- 1What is oscillatory motion?
- 2Name two examples of oscillatory motion.
- 3What is random motion?
- 4Give two examples of random motion.
- 5Which motion does a pendulum of a wall clock show?
- 6What happens to a thin metal strip pushed gently downward and released?
- 7A ball moves between A and B and passes O each time. How many times does it pass O in 3 complete to-and-fro trips (A→B→A)?
- 8Aarav says a fly buzzing in a room and a swing both show oscillatory motion. Correct him.
Show answers (try them yourself first)
- 1Continuous to-and-fro motion along the same path.
- 2A swing and a plucked sitar string.
- 3Motion in different directions with no fixed path.
- 4A butterfly near flowers and ants scattered by salt water.
- 5Oscillatory motion
- 6It vibrates for some time (oscillatory motion).
- 72 times per trip, so 3 × 2 = 6 times.
- 8The swing is oscillatory (same path); the fly is random (no fixed path).
Nonlinear motion and combined motions
Look at a sewing machine at work. The cloth slides straight, the big wheel turns round, the needle jumps up and down. Many kinds of motion happen together, like a small orchestra.
Nonlinear motion (अरेषीय गती) is any motion not along a straight line: circular, oscillatory and random motion. The two main kinds of motion are linear and nonlinear.
In the figure : In the figure the four paths show A linear, B circular, C oscillatory and D random motion. Circular, oscillatory and random motions are nonlinear.
Rule 1: Linear and nonlinear — Random, circular and oscillatory motions are not in one line, so they are nonlinear.
- Easy : Straight path → linear.
- Medium : Circle, to-and-fro or zigzag → nonlinear.
- Exam-type : Of 4 types (linear, circular, oscillatory, random), 3 are nonlinear and 1 is linear.
In the figure : In the figure of the toy car, A moves in a straight line (linear), the fan B moves in a circle and the ball C swings to and fro. Different types of motion can occur together.
Rule 2: Combined motions — In a sewing machine the cloth moves in a straight line, the wheel in a circle and the needle up and down. The foot pedal moves up and down, but the end of the connecting rod near the axis of the large wheel moves in a circle.
- Easy : Sewing machine: cloth (linear), wheel (circular), needle (up and down).
- Medium : The pedal moves up and down while the rod end goes round: two motions together.
- Exam-type : A bicycle: the cycle goes straight, wheels turn in circles, pedals go round, the bell shakes when it rings.
Linear = one kind; Nonlinear = circular, oscillatory and random. Many machines combine motions.
Thinking a machine has only one kind of motion. Most have several together.
Memory clue: L-C-O-R: Linear, Circular, Oscillatory, Random – only L is straight.
Spot the difference
| Motion | Kind |
|---|---|
| Linear | Linear |
| Circular | Nonlinear |
| Oscillatory and random | Nonlinear |
Practice questions
- 1What is nonlinear motion?
- 2Name the types of nonlinear motion.
- 3What are the two main kinds of motion?
- 4Which motion does the cloth in a sewing machine show?
- 5Which motion does the needle of a sewing machine show?
- 6Give one machine with several motions together.
- 7In a bicycle ride, name the motion of (a) the cycle, (b) the wheel, (c) the bell when rung.
- 8Meena says a swing and a merry-go-round show the same nonlinear motion. Correct her.
Show answers (try them yourself first)
- 1Motion that is not along a straight line.
- 2Circular, oscillatory and random.
- 3Linear and nonlinear.
- 4Linear motion
- 5Up-and-down (oscillatory) motion.
- 6Sewing machine
- 7(a) linear, (b) circular, (c) oscillatory.
- 8Both are nonlinear, but the swing is oscillatory and the merry-go-round is circular.
Quick revision
- Motion means a continuous change of position; it is judged with respect to a fixed reference point.
- Linear motion is along a straight line; circular, oscillatory and random motions are nonlinear.
- Different types of motion can occur together, e.g. in a sewing machine.