Chapter 3 · Section 2Textbook pages 57–59

Galileo and Newton's First Law ന്യൂട്ടന്റെ ഒന്നാം ചലനനിയമം

For two thousand years people believed that a moving object needs a force to keep it moving – push a cart and stop pushing, and it stops. About four hundred years ago Galileo rolled balls along slopes and showed this is wrong. Newton then turned the idea into his first law of motion. Here you repeat Galileo's experiment in a virtual channel.

📖 What you need (page 5 of this guide)

1. Galileo's observations (Fig 3.5)

ഏകദേശം നാല് നൂറ്റാണ്ടുകൾക്കു മുമ്പ് ഗലീലിയോ നടത്തിയ പരീക്ഷണത്തിന്റെ മറ്റൊരു രൂപമാണ് ഇവിടെ നൽകിയിരിക്കുന്നത്. – Here is another form of the experiment Galileo did about four centuries ago. Bend a wiring channel into a U. Release a marble (ഗോലി) from the end A. Then lower the other end C step by step until that arm is horizontal, releasing the marble from A each time.

⚠ Real experiment: use a plastic wiring channel or a curtain rail and a glass marble or small steel ball. Do it on the floor or a large table so the ball cannot roll off and fall on someone's foot, and keep marbles away from small children (choking hazard).
🎬 Fig 3.5 (a)–(d): lowering end C (a real channel – a little friction)
🧪 Galileo's channel – your own trials
Friction:
Slope of BCFrictionHeight reached on BC (cm)Height of A (cm)Distance rolled along BC

Model: A is 30 cm above the bottom B; arm AB slopes at 45°. The ball rolls without slipping, and friction (rolling resistance) takes away a little energy for every metre it rolls. With no friction it climbs back to exactly the height of A, whatever the slope – and on a horizontal arm it never stops.

Textbook questions (pages 57–58)

  1. ഓരോ സന്ദർഭത്തിലും വയറിങ് ചാനലിലെ A എന്ന ഭാഗത്തു നിന്ന് ഒരു ഗോലി ഉരുട്ടി വിട്ടാൽ എന്തൊക്കെ നിരീക്ഷിക്കും? What do you observe each time the marble is released from A?
  2. ഓരോ സന്ദർഭത്തിലും ഗോലി സഞ്ചരിച്ച ദൂരം കൂടിയോ അതോ കുറഞ്ഞോ? Did the distance travelled by the marble increase or decrease each time?
  3. ഗോലി ഏറ്റവും കൂടുതൽ ദൂരം സഞ്ചരിച്ചത് ഏത് സന്ദർഭത്തിലാണ്? When did it travel the farthest?
1. The marble rolls down AB and up the other arm, rising to almost the same height as A before it stops and rolls back.
2. The distance increased each time the slope of BC was made smaller: to climb to the same height on a gentler slope, it must roll farther.
3. In Fig 3.5 (d), when arm BC is horizontal. There is no height to climb, so it rolls on and on – it stops only because of friction.

The textbook explains: ആദ്യം ഏത് ഉയരത്തിൽ നിന്ന് പതിച്ചുവോ ആ ഉയരം വരെ എത്താനുള്ള ശ്രമം കാരണമാണ് ഗോലി കൂടുതൽ സഞ്ചരിച്ചത്. – the marble travels farther because it tries to reach the height from which it started.

More questions (page 58)

  1. എന്തുകൊണ്ടായിരിക്കാം കുറച്ചു ദൂരം കഴിഞ്ഞപ്പോൾ ഗോലി നിശ്ചലമായത്? Why did the marble come to rest after some distance?
  2. ഘർഷണം ഇല്ലായിരുന്നുവെങ്കിൽ എന്ത് സംഭവിക്കുമായിരുന്നു? What would have happened if there were no friction?
  3. ഒരു ബാഹ്യബലവും ഈ ഗോലിയിൽ പ്രയോഗിക്കപ്പെട്ടില്ലായിരുന്നു എങ്കിൽ എന്ത് സംഭവിക്കുമായിരുന്നു? What would have happened if no external force acted on the marble?
  4. ഇതിൽ നിന്നും നിങ്ങൾ എത്തിച്ചേർന്ന നിഗമനമെന്ത്? What is your conclusion?
4. Because of friction between the marble and the channel (and a little air resistance). Friction is an unbalanced external force acting opposite to its motion, so it slows the marble down and finally stops it.
5. On the horizontal arm it would never stop: it would keep rolling for ever with the same speed (set friction to “none” and the slope to 0° in the lab).
6. It would keep moving in a straight line with uniform speed for ever – nothing would change its motion.
7. To stop a moving object, an unbalanced external force must act against its motion; no force is needed to keep it moving uniformly in a straight line (the key box below).
⭐ Galileo's conclusion (textbook page 58)

ചലിക്കുന്ന ഒരു വസ്തുവിനെ നിശ്ചലമാക്കാൻ ചലനത്തിന്റെ എതിർദിശയിൽ അസന്തുലിതബാഹ്യബലം പ്രയോഗിക്കണം. ഒരു വസ്തുവിന് സമവേഗത്തിലുള്ള നേർരേഖാ ചലനം നിലനിർത്തുന്നതിന് ഒരു അസന്തുലിതബാഹ്യബലം ആവശ്യമില്ല.

To bring a moving object to rest, an unbalanced external force must act opposite to its motion. No unbalanced external force is needed to keep an object moving with uniform speed in a straight line.

Putting together what we learnt from the toy car (page 5) and Galileo's channel:

⭐ Toy car + Galileo (textbook page 58)

ഒരു വസ്തുവിന്റെ ചലനാവസ്ഥയ്ക്കോ നിശ്ചലാവസ്ഥയ്ക്കോ മാറ്റം വരുത്തുന്നതിന് ഒരു അസന്തുലിതബാഹ്യബലം ആവശ്യമാണ്.

An unbalanced external force is needed to change the state of motion or the state of rest of an object.

⚠️ The old wrong idea

The Greek thinker Aristotle taught that a moving object stops by itself unless something keeps pushing it. It looks true in daily life – a pushed cart soon stops – only because friction is always there, hidden. Galileo's channel shows the truth: take friction away and nothing is needed to keep the motion going.

📚 Galileo Galilei (ഗലീലിയോ ഗലീലി), 1564–1642
  • Born at Pisa, Italy (ഇറ്റലിയിലെ പിസ). From childhood he was interested in mathematics and philosophy.
  • His first scientific work, “La Bilancetta” (The Little Balance), described Archimedes' method of finding relative density (ആപേക്ഷിക സാന്ദ്രത) with a balance. The textbook dates it to 1581 (many historians give 1586).
  • With a telescope he made himself he observed Saturn and Venus, and argued that all the planets go round the Sun.
  • His experiments with slopes (inclined planes) gave the first clues about inertia (ജഡത്വം) – the next page.

2. Newton's first law of motion

ഗലീലിയോയെപ്പോലെയുള്ള മുൻഗാമികളുടെ ശാസ്ത്രനിരീക്ഷണങ്ങളെ ന്യൂട്ടൻ അപഗ്രഥിച്ചു പഠിക്കുകയും അവ ക്രോഡീകരിക്കുകയും ചെയ്തു. Newton studied the observations of earlier scientists like Galileo and organised them. That helped him find new conclusions and laws about motion and about objects acted on by forces.

⭐ Newton's first law of motion (textbook page 59)

അസന്തുലിതമായ ബാഹ്യബലത്തിന് വിധേയമാകുന്നതുവരെ ഓരോ വസ്തുവും നിശ്ചലാവസ്ഥയിലോ നേർരേഖയിലുള്ള സമചലനത്തിലോ തുടരും. ഇതാണ് ന്യൂട്ടന്റെ ഒന്നാം ചലനനിയമം.

Every object continues in its state of rest, or of uniform motion in a straight line, unless it is acted upon by an unbalanced external force.

🎬 The first law in pictures (positions every 0.5 s)

The first law helps us define two physical quantities: force and inertia.

Q. എന്താണ് ബലം? – What is force?

ഒരു വസ്തുവിന്റെ നിശ്ചലാവസ്ഥയ്ക്കോ നേർരേഖാ സമചലനത്തിനോ മാറ്റം വരുത്താനോ അതിനുള്ള പ്രവണത ഉളവാക്കാനോ വേണ്ടി ആ വസ്തുവിൽ പ്രയോഗിക്കേണ്ടത് എന്താണോ അതാണ് ബലം.
Force is that which must act on an object to change, or to tend to change, its state of rest or of uniform motion in a straight line. Why “tend to”: pushing a wall does not move it, but your push still tries to change its state – it is still a force.
📚 Sir Isaac Newton (സർ ഐസക് ന്യൂട്ടൻ), 1643–1727
  • Born in England. A philosopher, physicist, mathematician and astronomer.
  • He showed that the motion of objects on the Earth and the motion of the heavenly bodies obey the same natural laws.
  • His book Principia Mathematica explains gravitation and the laws of motion – the foundation of mechanics (ബലതന്ത്രം).
  • The corpuscular theory of light and calculus are among his contributions; he is called the father of calculus.
  • He built the first reflecting telescope.
🌴 Kerala connection

A country boat on the Vembanad backwaters keeps gliding long after the boatman lifts his pole out of the water – it keeps its motion. It slowly stops only because the water drags on it (an unbalanced force against the motion). Out in space there is no such drag: after its engines stop, a spacecraft like Chandrayaan-3 coasts on for thousands of kilometres without any push – the first law at work. (Gravity still bends its path; more on that in Chapter 4.)

🌐 Explore online needs internet · opens in a new tab

3. Check yourself

🧭 Summary

Next: Inertia and mass ▶