Force and Motion: Speed, Velocity, Acceleration, Graphs and Newton's Laws — REET Notes
This page covers distance-displacement, speed-velocity, acceleration, graphs and equations of motion, uniform circular motion, types of force, resultant force and Newton's laws, all at the Class 8-9 NCERT level. REET 2024 Level 2 drew definition, calculation and graph-reading questions straight from this range, and a little practice is enough to secure full marks here.
- 4 questions in REET 2024
- Class 8-9 NCERT level
- 9 min read
How REET asks this topic
REET 2024 Level 2 (Maths-Science) carried 4 questions from Force and Motion: the definition of uniform circular motion, the resultant of two forces acting in opposite directions, the total distance covered by a car travelling in two stages (with a unit change between km/h and minutes), and identifying the distance-time graph of motion at constant speed. In short, expect Class 8-9 NCERT-level definitions, unit conversions, short calculations and graph reading. Newton's laws, inertia and momentum also fall within this same range.
Motion, distance-displacement, and speed-velocity
An object is said to be in motion if its position changes with time relative to some reference point; motion and rest are both relative — a passenger sitting in a moving bus is at rest relative to the bus, but in motion relative to the road.
Distance is the total length of the path travelled by an object — it has only magnitude, so it is a scalar quantity. Displacement is the shortest distance between the initial and final position, along with direction — it is a vector quantity. Displacement can be zero while distance is not: completing one full lap of a 400 m track gives a distance of 400 m but zero displacement.
Speed = distance / time (a scalar); velocity = displacement / time, in a definite direction (a vector). Both have the SI unit m/s. Average speed = total distance / total time. Unit conversion: 1 km/h = 5/18 m/s, so 36 km/h = 10 m/s and 18 km/h = 5 m/s. The REET 2024 question worked out to: 18 km/h × (10/60) h = 3 km and 36 km/h × (15/60) h = 9 km, for a total of 12 km.
Types of motion and acceleration
| Concept | Meaning | Example / formula |
|---|---|---|
| Uniform motion | Equal distances covered in equal time intervals | A car moving at constant speed on a straight road |
| Non-uniform motion | Unequal distances covered in equal time intervals | A bus moving through crowded traffic |
| Acceleration | Change in velocity per unit time | a = (v - u)/t; unit m/s² |
| Retardation | Negative acceleration when velocity decreases | A car slowing down as brakes are applied |
| Uniform circular motion | Uniform speed on a circular path; direction changes every instant, so velocity keeps changing and the motion is accelerated | v = 2πr/t; a satellite orbiting the earth, a stone whirled on a string |
In uniform circular motion, speed stays constant but velocity does not — REET 2024 tested exactly this distinction.[Source 1]
Graphs and the equations of motion
| Graph / equation | What it tells us |
|---|---|
| Distance-time graph: a sloped straight line | Constant (uniform) speed; the slope equals the speed. Whether the line starts at the origin or at some initial distance, the speed remains constant in both cases |
| Distance-time graph: a line parallel to the time axis | The object is at rest |
| Distance-time graph: a curve | Non-uniform speed |
| Velocity-time graph | Slope = acceleration; the area under the graph = displacement |
| First equation | v = u + at |
| Second equation | s = ut + ½at² |
| Third equation | v² - u² = 2as |
u = initial velocity, v = final velocity, a = uniform acceleration, t = time, s = displacement. These equations apply only under uniform acceleration.[Source 1]
Force: types and effects
Force is a push or pull applied to an object, arising from the interaction between two objects. Force can change an object's state of motion (from rest to motion, or motion to rest), its speed, its direction of motion, and its shape. The SI unit of force is the newton (N).
Contact forces act by touching the object — muscular force (bullocks pulling a plough) and friction (a rolling ball coming to a stop). Non-contact forces act without touching — magnetic force, electrostatic force (a rubbed comb attracting bits of paper) and gravitational force.
Forces acting on the same object in the same direction add up, and when forces act in opposite directions, the resultant equals their difference and acts in the direction of the larger force — if forces of 5 N and 3 N act in opposite directions, the resultant is 2 N. When the resultant force is zero, the forces are called balanced; balanced forces do not change an object's state of motion. It is unbalanced force that produces acceleration in an object.
Newton's laws of motion, inertia and momentum
| Law / quantity | Statement | Everyday example |
|---|---|---|
| First law (law of inertia) | An object continues in its state of rest or of uniform motion in a straight line unless acted upon by an unbalanced external force | Passengers lean backward when a bus suddenly starts moving; dust shaken out of a carpet |
| Inertia | The tendency to resist a change in state; mass is the measure of inertia | Pushing a loaded cart is harder than pushing an empty one |
| Momentum | p = m × v; a vector; unit kg·m/s | A slow-moving heavy truck can carry more momentum than a fast-moving ball |
| Second law | The rate of change of momentum is proportional to the applied unbalanced force and acts in the direction of the force: F = m × a | 1 N = 1 kg·m/s²; a cricket fielder draws the hand backward while catching a ball to reduce the force experienced |
| Third law | For every action there is an equal and opposite reaction; the two forces act on two different objects | A gun recoils when a bullet is fired; rockets; a boat moves backward when someone jumps off it |
| Conservation of momentum | If no external unbalanced force acts, the total momentum of a system stays constant | The total momentum of a gun and bullet is zero both before and after firing |
How to teach this to children
Classroom activity (Class 6-8)
Mark out 50 m on the school playground; have children walk, walk fast and run in groups, noting the time taken, then calculate speed = distance/time. Follow this by tabulating distance against time and plotting a distance-time graph on graph paper.
Teaching aids
For inertia, place a postcard on a glass with a coin on top and flick the card away sharply — the coin falls into the glass. For the third law, inflate a balloon and release it along a straw threaded on a string — a 'balloon rocket'.
Common misconceptions
'A moving object needs a continuous force to keep moving', 'a heavier object always falls faster', 'distance and displacement are the same thing', and 'action and reaction cancel each other out'. The role of friction, the full-lap example, and the reminder that 'the two forces act on different objects' all help clear these up.
Assessment idea
Show children three different graphs (a sloped line, a horizontal line, a curve) and ask which shows an object at rest, which shows constant speed and which shows changing speed; pair this with two questions on converting km/h to m/s.
Memory trick / exam tip
km/h to m/s: multiply by 5/18; m/s to km/h: multiply by 18/5. When time is given in minutes, convert it to hours first (10 minutes = 1/6 h, 15 minutes = 1/4 h). For graph questions, remember: 'sloped straight line = constant speed, flat line = at rest, curved line = changing speed'.
REET 2024 questions (solved)
Question 133
The motion of an object is said to be uniform circular motion, if the object
- Aवृत्तीय पथ पर परिवर्ती चाल से चलती है
- Bवृत्तीय पथ पर एक समान त्वरण से चलती है
- Cवृत्तीय पथ पर एक समान चाल से चलती है
- Dवृत्तीय पथ पर एक समान वेग से चलती है
Explanation
जब कोई वस्तु वृत्तीय पथ पर एक समान चाल (constant speed) से चलती है, तो उसकी गति एक समान वृत्तीय गति कहलाती है। इसमें चाल स्थिर रहती है पर हर बिन्दु पर गति की दिशा बदलती है, इसलिए वेग स्थिर नहीं रहता। त्वरण का परिमाण स्थिर पर दिशा (केंद्र की ओर) बदलती रहती है, अतः 'एक समान वेग' वाला विकल्प गलत है।
Question 141
Two forces of 5 N and 3 N are acting on the same object in opposite directions, the resultant force on the object will be
- A15 N
- B8 N
- C0.6 N
- D2 N
Explanation
विपरीत दिशाओं में लगे बलों का परिणामी बल उनके अन्तर के बराबर होता है और बड़े बल की दिशा में कार्य करता है। अतः परिणामी बल = 5 N − 3 N = 2 N। 8 N तब होता जब दोनों बल एक ही दिशा में लगते।
Question 128
A car travels at a speed of 18 km/h for 10 minutes, subsequently it travels at a speed of 36 km/h for 15 minutes, then the total distance covered by this car will be
- A3 km
- B9 km
- C12 km
- D27 km
Explanation
दूरी = चाल × समय। पहले भाग में 18 km/h × (10/60) h = 3 km। दूसरे भाग में 36 km/h × (15/60) h = 9 km। कुल दूरी = 3 + 9 = 12 km।
Question 132
The correct distance – time graphs showing the motion of an object moving with a constant speed in linear motion are
Figure: Four distance-time graphs: (i) a curve bending upward from the origin, (ii) a straight line through the origin, (iii) a horizontal line, (iv) a straight line offset from the origin. Diagram added with the exact shapes from the official figure note. Graphs (ii) and (iv) both show constant speed, matching the stored answer.
- A(i) व (iii) दोनों
- B(ii) व (iv) दोनों
- C(i) व (ii) दोनों
- D(iii) व (iv) दोनों
Explanation
नियत चाल से रेखीय गति में दूरी समय के साथ समान दर से बढ़ती है, इसलिए दूरी-समय ग्राफ एक सीधी झुकी हुई रेखा होता है। ग्राफ (ii) मूल बिंदु से और ग्राफ (iv) कुछ प्रारम्भिक दूरी से शुरू होने वाली सीधी रेखा है — दोनों नियत चाल दर्शाते हैं। ग्राफ (i) वक्र है (चाल बढ़ रही है) और (iii) क्षैतिज रेखा है (वस्तु विराम में है)।
Practice questions
Question 1
The SI unit of force, newton, is equal to
- Akg·m/s
- Bkg·m/s²
- Ckg·m²/s
- Dkg/m·s²
Explanation
From F = m × a, 1 N = 1 kg × 1 m/s² = 1 kg·m/s². kg·m/s is the unit of momentum, not force.
Question 2
A car starting from rest attains a velocity of 20 m/s in 5 s. Its acceleration is
- A100 m/s²
- B25 m/s²
- C4 m/s²
- D0.25 m/s²
Explanation
a = (v - u)/t = (20 - 0)/5 = 4 m/s². 100 comes from multiplying instead of dividing, and 0.25 from inverting the fraction.
Question 3
The slope of a velocity-time graph gives
- Aदूरी
- Bविस्थापन
- Cचाल
- Dत्वरण
Explanation
The slope of a velocity-time graph equals change in velocity divided by time, which is acceleration. The area under the graph gives displacement.
Question 4
The inertia of an object depends on its
- Aआयतन पर
- Bद्रव्यमान पर
- Cवेग पर
- Dआकार पर
Explanation
Mass is the measure of inertia — an object with greater mass is harder to set in motion or to stop.
Question 5
A ball of mass 2 kg moves with a velocity of 3 m/s. Its momentum is
- A1.5 kg·m/s
- B5 kg·m/s
- C6 kg·m/s
- D9 kg·m/s
Explanation
p = m × v = 2 × 3 = 6 kg·m/s. 5 comes from adding instead of multiplying, and 1.5 from dividing.
Question 6
A person completes exactly one round of a 400 m circular track and returns to the starting point. The distance and displacement are respectively
- A400 m और 400 m
- B0 और 400 m
- C400 m और 0
- D0 और 0
Explanation
The length of the path covered (distance) is 400 m, but since the initial and final positions are the same, the displacement is zero.
Question 7
The recoil of a gun when a bullet is fired is an example of
- Aन्यूटन का प्रथम नियम
- Bन्यूटन का द्वितीय नियम
- Cन्यूटन का तृतीय नियम
- Dगुरुत्वाकर्षण का नियम
Explanation
The forward force on the bullet (action) produces an equal and opposite force on the gun (reaction), which is exactly Newton's third law.
Question 8
Which of the following is a non-contact force?
- Aपेशीय बल
- Bघर्षण बल
- Cचुंबकीय बल
- Dहाथ से धकेलने का बल
Explanation
A magnet attracts iron without touching it, so magnetic force is a non-contact force. Muscular force, friction and pushing with the hand are all contact forces.
Question 9
The most suitable Class 8 activity to give first-hand experience of inertia is
- Aगिलास पर रखे कार्ड को झटकने पर उस पर रखे सिक्के का गिलास में गिरना दिखाना
- Bन्यूटन की जीवनी पढ़वाना
- CF = ma सूत्र दस बार लिखवाना
- Dजड़त्व की परिभाषा श्यामपट्ट पर लिखना
Explanation
The card moves away quickly, but the coin, due to inertia, stays in its state of rest and drops into the glass — children see the concept happen with their own eyes. The other options are pure information or rote learning.
Question 10
A learner says, ‘The rolling ball stopped because the force pushing it forward ran out.’ What should the teacher clarify to correct this misconception?
- Aगति बनाए रखने के लिए लगातार बल आवश्यक है
- Bघर्षण जैसा असंतुलित बल गेंद को रोकता है; बल न हो तो गेंद एकसमान गति में चलती रहती
- Cभारी गेंद कभी नहीं रुकती
- Dगुरुत्वाकर्षण गेंद को आगे धकेलता है
Explanation
Newton's first law says no force is needed to keep an object moving; the ball stops because of an unbalanced force like friction acting against it. Option A restates the very misconception that needs correcting.
Frequently asked questions
How many questions come from Force and Motion in REET Level 2?+
The number isn't fixed, but REET 2024 Level 2's two shifts of Maths-Science carried 4 questions from this topic in total — on definitions, resultant force, distance calculation and distance-time graphs.
Why is uniform circular motion an accelerated motion?+
Because although the speed stays constant, the direction changes at every instant; a change in direction is a change in velocity, and a change in velocity is, by definition, acceleration.
What is the SI unit of force?+
The newton (N). 1 N is the force that produces an acceleration of 1 m/s² in a mass of 1 kg.
What does inertia depend on?+
On the mass of the object. The greater the mass, the greater the inertia.
Read next
Official Sources
Change Log
- 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked