Chapter 2 · Section 5Textbook pages 37–40

Uniform Acceleration and Road Safety സമത്വരണം, അസമത്വരണം · റോഡ് സുരക്ഷ

The bus of Table 2.6 gained exactly 4 m/s in every 2 s; the motorbike of Table 2.7 lost its velocity unevenly. That is the difference between uniform and non-uniform acceleration. Then we use what we know about speed and braking to understand road safety: road signs, road markings, safe clothing at night – and a graph of road accidents in Kerala.

📖 What you need (pages 3 and 8 of this guide)

1. Uniform and non-uniform acceleration

Q1. പട്ടിക 2.6 ൽ ലഭിച്ച ത്വരണം ഓരോ അവസരത്തിലും തുല്യമായിരുന്നോ? – Was the acceleration found in Table 2.6 the same each time?

Yes – 2 m/s² from A to B, B to C and C to D.
Why: in every 2 s interval the bus's velocity rose by the same 4 m/s.

Q2. പട്ടിക 2.7 പ്രകാരം ലഭിച്ച ത്വരണമോ? – And the acceleration found in Table 2.7?

No – it was −0.5, −1, −1 and −0.25 m/s²: different in different stages.
Why: the motorbike lost 5 m/s each time, but in different times (10 s, 5 s, 5 s, 20 s). In equal intervals of time, the change in velocity is not equal.
📈 Equal steps or unequal steps?
⭐ Uniform and non-uniform acceleration (textbook page 37)

ഒരു വസ്തുവിന്റെ പ്രവേഗമാറ്റത്തിന്റെ അളവ് തുല്യ ഇടവേളകളിൽ തുല്യമായിരുന്നാൽ അത് സമത്വരണത്തിലാണ് (uniform acceleration). എന്നാൽ, ഒരു വസ്തുവിന്റെ പ്രവേഗമാറ്റത്തിന്റെ അളവ് തുല്യ ഇടവേളകളിൽ വ്യത്യസ്തമായിരുന്നാൽ അത് അസമത്വരണത്തിലാണ് (non uniform acceleration).

If the change in velocity of an object is equal in equal intervals of time, it is in uniform acceleration (സമത്വരണം). If the change in velocity is different in equal intervals of time, it is in non-uniform acceleration (അസമത്വരണം). On a velocity–time graph, uniform acceleration is a single straight line; non-uniform acceleration bends.

The equations of motion on page 11 work only for uniform acceleration – so this idea matters.

2. Road safety – who must follow the rules?

വാഹനങ്ങളുടെ അമിതവേഗം അപകടങ്ങൾക്ക് കാരണമാകുന്നു. അപകടങ്ങൾ കുറയ്ക്കാൻ നാം റോഡ് നിയമങ്ങൾ നിർബന്ധമായും പാലിക്കേണ്ടതാണ്. – Over-speeding of vehicles causes accidents; to reduce them we must follow road rules. A faster vehicle needs a much longer distance to stop (page 15 shows the stopping distance grows with the square of the speed).

Q3. വാഹനങ്ങളുടെ അമിത വേഗം മാത്രമാണോ അപകടങ്ങൾക്കു കാരണം? കാൽനടക്കാരും റോഡ് നിയമങ്ങൾ പാലിക്കേണ്ടതല്ലേ? – Is over-speeding the only cause of accidents? Shouldn't pedestrians also follow road rules?

No, speed is not the only cause – careless crossing, walking on the wrong side, using a phone while walking, poor visibility at night, drunk driving and bad roads also cause accidents. Yes, pedestrians must follow the rules too.
Why: a road is shared. Even a careful driver cannot stop in time if a pedestrian suddenly runs across closer than the vehicle's stopping distance.
കാൽനടക്കാർ പാലിക്കേണ്ട റോഡ് നിയമങ്ങൾ ഏതൊക്കെയായിരിക്കും? – The thinking boy asks: which road rules should pedestrians follow? The textbook gives two:
  • Use the footpath or a foot-over-bridge wherever there is one.
  • Before crossing: stop at the kerb, look right – left – right again (in India vehicles keep to the left, so the nearest lane's traffic comes from your right), cross only when it is clear.
  • Walk across – do not run, and do not cross from between parked vehicles.
  • No phone calls or earphones while crossing.
  • At night or in heavy rain, wear light or bright clothes, or a reflective strip; carry a torch.
  • Hold small children's hands and walk in single file on narrow roads.
Why walk facing the traffic? You can see the vehicles coming towards you and step aside in time.

3. Road signs – Fig 2.10

റോഡ് സൈനുകളെ പ്രധാനമായും മൂന്നായി തരം തിരിക്കാം. Road signs are mainly of three kinds. Notice the boards along a road: some are circles, some triangles, some rectangles – the shape itself tells you the kind of message.

KindShapeMessageTextbook examples
Mandatory signs
മാൻഡേറ്ററി സൈനുകൾ		red circlerules you must obey (നിർബന്ധമായും പാലിക്കേണ്ടവ)no parking · cycles prohibited · horn prohibited
Cautionary signs
കോഷനറി സൈനുകൾ		red trianglewarnings about the road ahead (ജാഗ്രതാ സൂചക ചിഹ്നങ്ങൾ)hump · narrow bridge · school ahead
Informatory signs
ഇൻഫോമേറ്ററി സൈനുകൾ		blue rectangleuseful information: directions, distances, facilities (അടിസ്ഥാനവിവര സൂചകങ്ങൾ)petrol pump · police station · hospital
🚦 Sign-sorting game

For each sign, choose its kind: M = mandatory, C = cautionary, I = informatory. The nine textbook signs are here, plus three more you will see on Kerala roads.

Score: 0 of 0
🖍️ Activity (page 39)

മുകളിൽ സൂചിപ്പിച്ച സൈനുകൾക്ക് പുറമേ ഓരോ വിഭാഗത്തിലുമുള്ള കൂടുതൽ ചിഹ്നങ്ങൾ ശേഖരിച്ച് പ്രത്യേകം പോസ്റ്ററുകൾ തയ്യാറാക്കി സ്കൂൾ ബുള്ളറ്റിൻ ബോർഡിൽ പ്രദർശിപ്പിക്കുക. – Collect more signs of each kind, make a separate poster for each kind and put them up on the school bulletin board. Ideas: mandatory – no entry, speed limit, stop, compulsory left turn; cautionary – sharp bend, slippery road, men at work, cattle; informatory – parking, bus stop, first aid, eating place.

4. Road markings – Fig 2.11

Lines painted on the road also give rules. Press Play.

🛣️ Road-marking lab (top view; vehicles keep left and move up the screen)
FigMarkingMeaning
2.11 (a)broken (dashed) white centre lineവാഹനങ്ങൾക്ക് നിയന്ത്രിതമായി മുറിച്ചുകടക്കാൻ കഴിയുന്നവ – vehicles may cross it carefully, e.g. to overtake when the road ahead is clear
2.11 (b)solid / double yellow lineവാഹനങ്ങൾക്ക് മുറിച്ച് കടക്കാൻ പാടില്ലാത്തവ – vehicles must not cross it (no overtaking: bends, bridges, hills)
2.11 (c)zebra crossingസീബ്രാ ക്രോസിങ് – the place for pedestrians to cross; vehicles must stop and let them cross

5. Dark clothes at night

റോഡ് നിയമങ്ങൾ അനുസരിക്കാത്തതുകൊണ്ടു മാത്രമാണോ അപകടങ്ങൾ സംഭവിക്കുന്നത്? – The thinking girl asks: do accidents happen only because road rules are broken?
No. മങ്ങിയ വെളിച്ചത്തിൽ കടും നിറത്തിലുള്ള വസ്ത്രങ്ങൾ ധരിച്ച് റോഡരികിലൂടെ നടന്നു പോകുന്നവരെയും റോഡ് മുറിച്ചു കടക്കുന്നവരെയും മറ്റും ഡ്രൈവർമാർക്കു കാണാൻ കഴിയാതെ വരാം. ഈ സമയങ്ങളിൽ ഇളം നിറത്തിലുള്ള വസ്ത്രം ധരിക്കുന്നതല്ലേ ഉചിതം. In dim light, drivers may not see people in dark clothes walking along or crossing the road – this invites accidents even when nobody breaks a rule. At such times it is better to wear light-coloured clothes.
Why: a driver needs to see you before the stopping distance. Try it below.
🌙 Can the driver stop in time?

Model (approximate values used in road-safety campaigns): with dipped headlights a driver first notices a pedestrian in dark clothes at about 25 m, medium colours 40 m, white/light clothes 80 m, a reflective strip 150 m. Reaction time 1.5 s; braking retardation 7 m/s² on a dry road, 5 m/s² on a wet one. Stopping distance = (speed × reaction time) + speed² ÷ (2 × retardation).

6. Seminar – students and road safety

വിദ്യാർഥികളും റോഡ് സുരക്ഷയും എന്ന വിഷയത്തെ അടിസ്ഥാനപ്പെടുത്തി ഒരു സെമിനാർ പേപ്പർ തയ്യാറാക്കി അവതരിപ്പിക്കൂ. – Prepare and present a seminar paper on "Students and road safety". Hints (സൂചന):

  1. Introduction – why road safety matters to students (we walk, cycle and travel by bus every day).
  2. Crossing – zebra crossings, signals, look right–left–right, never from between parked buses.
  3. Groups – walk in single file on narrow roads; do not spread across the road; no pushing near the edge.
  4. Games – never play cricket or football near the road; a ball rolling onto the road is followed by a child.
  5. No licence, no driving – the law forbids it; a beginner cannot judge speed and stopping distance.
  6. Safe cycling – keep left, ride in single file, use a bell, lights and reflectors, wear a helmet, no double riding.
  7. Signals and signs – meanings of red/amber/green, the three kinds of signs, road markings.
  8. The physics – a vehicle cannot stop instantly: stopping distance = reaction distance + braking distance; doubling speed roughly quadruples the braking distance.
  9. Night and monsoon – light clothes, reflective strips, longer stopping distances on wet roads.
  10. Conclusion – a pledge and posters for the school.

7. Road accidents in Kerala – Graph 2.1

2016 മുതൽ 2022 വരെ കേരളത്തിൽ ഉണ്ടായ റോഡപകടങ്ങളുടെ എണ്ണത്തെ സംബന്ധിച്ച ഗ്രാഫ് ചുവടെ നൽകിയിരിക്കുന്നു. – The graph shows the number of road accidents in Kerala from 2016 to 2022 (source: official website of Kerala Police). Scale: X-axis 1 cm = 1 year, Y-axis 1 cm = 10000 accidents. Step through to redraw it.

📊 Graph 2.1 redrawn

Values are approximate – read from the textbook graph (to the nearest 500), not official figures.

Q4. ഗ്രാഫിൽ നിന്ന് എന്തെല്ലാം വിവരങ്ങളാണ് മനസ്സിലാക്കാൻ സാധിക്കുന്നത്? കണ്ടെത്തിയ വിവരങ്ങൾ ലിസ്റ്റ് ചെയ്യൂ. – What information can you get from the graph? List it.

  • The number of road accidents in each year from 2016 to 2022, and how it changed year by year.
  • From 2016 to 2019 it stayed high, close to 40,000 a year (a small dip in 2017).
  • It fell sharply in 2020 (about 27,000 – the lowest).
  • After 2020 it rose again: about 33,000 in 2021 and about 43,000 in 2022 – the highest of these years.
  • In most of these years there were more than 100 accidents a day (40,000 ÷ 365 ≈ 110).
Why the 2020 dip? During the COVID-19 lockdown far fewer vehicles were on the road. As traffic returned, accidents rose again – so the number of accidents depends on how we use the roads.

Q5 (page 41). ഏത് വർഷമാണ് ഏറ്റവും കുറവ് അപകടങ്ങൾ ഉണ്ടായത്? – In which year were there the fewest accidents?

2020 (about 27,000).
Why: it is the lowest point of the graph.

Q6 (page 41). 2019 ൽ എത്ര അപകടങ്ങൾ ഉണ്ടായിട്ടുണ്ട്? – How many accidents were there in 2019?

About 40,000.
Why: the 2019 point is at 4 cm on the Y-axis, and 1 cm = 10000, so 4 × 10000 = 40,000.
🌴 Kerala connection

Kerala has one of the highest numbers of vehicles per person in India, and many of our roads are narrow and busy. The Kerala Police and the Motor Vehicles Department run road-safety drives in schools, and NATPAC (National Transportation Planning and Research Centre, Thiruvananthapuram) studies "black spots" where accidents happen again and again. In the monsoon, wet roads lengthen stopping distances and dark evenings hide pedestrians – exactly the physics of this page.

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8. Check yourself

🧭 Summary

Next: Position–time and velocity–time graphs ▶