Energy Transformation and Conservation of Energy ഊർജപരിവർത്തനം · ഊർജസംരക്ഷണ നിയമം
A fan turns electricity into motion, an iron box turns it into heat, a balloon car turns the stretch of rubber into speed. Energy keeps changing its form – but does any of it get lost on the way? On this page you follow energy through machines and toys, and then check with a 1000 kg pile-driver hammer that the total energy stays the same.
- Forms of energy: electrical, mechanical, heat, light, sound, chemical (pages 4 and 7).
- Potential energy Ep = mgh; kinetic energy Ek = ½mv² (pages 7–8).
- For a falling object starting from rest: v² = u² + 2gh with u = 0 (page 1).
1. Machines change the form of energy (page 119)
The thinking girl asks: എല്ലാ ഊർജരൂപങ്ങളെയും ഒരു രൂപത്തിൽ നിന്ന് മറ്റൊരു രൂപത്തിലേക്ക് മാറ്റാൻ കഴിയുമോ? – Can every form of energy be changed into another form?
വൈദ്യുതി ഉപയോഗിച്ച് ബൾബുകൾ പ്രകാശിപ്പിക്കാറുണ്ടല്ലോ. മോട്ടോർ പമ്പ് ഉപയോഗിച്ച് ജലം പമ്പ് ചെയ്യാറില്ലേ? – We light bulbs with electricity and pump water with a motor pump. In daily life we keep changing energy from one form to another, and machines make this easy. This is called energy transformation (ഊർജപരിവർത്തനം). The textbook starts the list:
- വൈദ്യുതമോട്ടോർ വൈദ്യുതോർജത്തെ യാന്ത്രികോർജമാക്കി മാറ്റുന്നു. – An electric motor changes electrical energy into mechanical energy.
- പെട്രോൾകാറുകൾ രാസോർജത്തെ ഗതികോർജമാക്കി മാറ്റുന്നു. – Petrol cars change chemical energy into kinetic energy.
Write a few more machines and their energy changes (ഏതാനും യന്ത്രങ്ങളും അവയിലെ ഊർജമാറ്റവും എഴുതിനോക്കൂ) – try before you look.
2. The balloon toy car (Fig 6.9)
നിങ്ങൾക്ക് ധാരാളം കളിപ്പാട്ടങ്ങൾ പരിചിതമാണല്ലോ. ഇവ ഓരോന്നിലും ഊർജപരിവർത്തനം എങ്ങനെയാണ് പ്രയോജനപ്പെടുത്തുന്നത് എന്ന് ശ്രദ്ധിച്ചിട്ടുണ്ടോ? – Toys use energy transformation too. ചിത്രത്തിൽ കാണിച്ചിരിക്കുന്നതുപോലെ ഒരു ബലൂൺ ടോയ് കാർ നിർമ്മിക്കാം. – Let us make a balloon toy car like the one in Fig 6.9: a plastic bottle on four wheels, with a balloon tied to a straw that points backwards.
| Trial | Balloon (cm) | Car | Floor | Stored energy (J) | Distance (m) |
|---|
Model (approx.): a balloon blown up to d cm across stores about 0.004 × d² J; about 5 % of it ends up as the car's kinetic energy (the rest goes into the rushing air, sound and heat); the car then rolls until friction turns its kinetic energy into heat.
Textbook questions (pages 119–120)
- ഇതിൽ ബലൂണിന് ടോയ് കാറിനെ ചലിപ്പിക്കാനാവശ്യമായ ഊർജം/ബലം എങ്ങനെ ലഭിക്കുന്നു? – How does the balloon get the energy/force to move the toy car?
- ബലൂൺ ഊതി വീർപ്പിക്കുമ്പോൾ ബലൂണിന്റെ റബ്ബറിന് എന്ത് മാറ്റമാണ് ഉണ്ടാവുന്നത്? – What happens to the rubber of the balloon when it is blown up?
- വീർപ്പിച്ച ബലൂണിൽ പ്രധാനമായും ഏത് ഊർജമാണുള്ളത്? – Which energy does the inflated balloon mainly have?
- കാർ ചലിക്കുമ്പോൾ ഊർജത്തിൽ എന്ത് മാറ്റമാണ് ഉണ്ടാകുന്നത്? – What change of energy takes place when the car moves?
2. The rubber is stretched – its shape (configuration) changes.
3. Potential energy due to configuration (stored in the stretched rubber and the squeezed air).
4. Potential energy → kinetic energy of the car (ടോയ് കാറിൽ ബലൂണിലെ സ്ഥിതികോർജം ഗതികോർജമായി മാറുന്നു). Finally friction turns the kinetic energy into heat (and a little sound) and the car stops.
🛠️ Build one yourself (ഇതുപോലൊരു കാർ നിർമ്മിക്കൂ)
- Take an empty 500 mL plastic bottle as the body. Tape two drinking straws across it as axle holders.
- Push two thin sticks (or skewers) through the straws as axles; fix bottle caps on the ends as wheels.
- Tie a balloon tightly to one end of a straw with a rubber band; tape the straw on top of the bottle so it points straight backwards.
- Blow up the balloon through the straw, pinch it, put the car on a smooth floor – and let go!
Q. നിങ്ങൾ നിർമ്മിച്ച ടോയ് കാർ മികച്ചതാകാൻ ഇതിന് എന്തെല്ലാം ഗുണങ്ങൾ ഉണ്ടായിരിക്കണം? – What qualities should your toy car have to be a good one? Compare the cars made by your classmates.
- A light body – less mass to speed up (try both cars in the lab).
- Wheels that turn freely with little friction at the axles, and wheels that are round, straight and well aligned.
- A nozzle (straw) pointing straight backwards, so all the push is forwards.
- A large balloon that can store more energy; no leaks at the joints.
- A smooth floor to run on.
3. Is energy lost when it changes form? – the pile driver (Fig 6.10)
The thinking boy asks: ഊർജമാറ്റം സംഭവിക്കുമ്പോൾ ഊർജത്തിന്റെ അളവ് കുറയുമോ? – Does the amount of energy decrease when energy changes form?
കെട്ടിടങ്ങളും പാലങ്ങളും നിർമ്മിക്കുമ്പോൾ അടിത്തറ ഉറപ്പിക്കുന്നതിനായി ചെയ്യുന്ന പൈലിങ് പ്രവർത്തനങ്ങൾ നിങ്ങൾ ശ്രദ്ധിച്ചിട്ടുണ്ടോ? പൈലിങ് യന്ത്രത്തിലെ ഹാമർ ശക്തിയായി പൈലിൽ പതിക്കുന്നതിന്റെ ഫലമായാണ് കുഴിയുണ്ടാകുന്നത്. – Have you noticed piling work done to make strong foundations for buildings and bridges? The hammer of the piling machine falls hard on the pile and drives it into the ground. In Fig 6.10 the hammer has a mass of 1000 kg and is 10 m above the top of the pile (g = 9.8 m/s²).
Work it out (pages 120–121). Find (i) the potential energy, kinetic energy and total energy of the hammer at the top; (ii) its velocity, kinetic energy, potential energy and total energy just before it touches the pile, when the top of the pile has gone down to ground level; (iii) compare the two totals.
At the top: u = 0, so Ek = 0 and Ep = mgh. At ground level: h = 0, so Ep = 0; find v² = u² + 2gh, then Ek = ½mv².
Q (page 121). ഹാമർ മുകളിലാകുമ്പോഴുള്ള ആകെ ഊർജവും തറനിരപ്പിൽ സ്പർശിക്കുന്ന അവസരത്തിലുള്ള ആകെ ഊർജവും താരതമ്യം ചെയ്യുമ്പോൾ നമുക്ക് എന്ത് നിഗമനത്തിലെത്തിച്ചേരാം? – Comparing the total energy at the top with the total energy at ground level, what can we conclude?
Hammer: 1000 kg from 10 m (g = 9.8 m/s²); with air resistance on, a steady drag of 3 % of its weight (approx.). Skater: 50 kg starting 5 m up a smooth U-shaped ramp; with friction on, a steady friction force of about 25 N (approx.). Notice that the total bar never changes – with friction, part of the energy simply becomes heat.
ഊർജം നിർമ്മിക്കുവാനോ നശിപ്പിക്കുവാനോ സാധ്യമല്ല. ഒരു രൂപത്തിലുള്ള ഊർജത്തെ ഊർജനഷ്ടമോ ലാഭമോ ഇല്ലാതെ മറ്റ് ഊർജരൂപങ്ങളിലേക്ക് മാറ്റാൻ കഴിയും. ഇതാണ് ഊർജസംരക്ഷണനിയമം.
Energy can neither be created nor destroyed. Energy in one form can be changed into other forms without any loss or gain. This is the law of conservation of energy.
No energy is destroyed. Friction and air resistance change kinetic energy into heat (and a little sound) that spreads into the floor and the air. The energy is still there, just in a form we cannot easily use again. That is why the "total" bar in the lab above stays the same even with friction on.
Q (page 121). പ്രവൃത്തിയും ഊർജവും തമ്മിലുള്ള സാമ്യങ്ങൾ എന്തെല്ലാമാണ്? – What are the similarities between work and energy? The textbook gives the first one: പ്രവൃത്തിയും ഊർജവും അദിശ അളവുകളാണ്. – Work and energy are both scalar quantities (അദിശ അളവ്).
• Both have the same unit, the joule (J) (also N m; and both can be given in kJ, cal or kcal).
• They are linked: energy is used up when work is done, and work done on an object is stored in it as energy (work done = energy transferred) – the hammer lifted 10 m gets 98 000 J because 98 000 J of work was done on it.
The textbook (page 120) suggests the PhET simulation “Energy Skate Park”. If your school computer has the PhET simulations installed, open it from the Science menu; otherwise use the link in the Explore box below (it needs internet). In it a skater rides a ramp you can reshape; you can switch on pie charts and bar graphs of kinetic, potential and thermal energy, and turn friction on and off – just like the skater in our lab above. Try to make the skater go higher than the starting point: you can't!
The tall pillars of the Kochi Metro and of bridges over Kerala's rivers and backwaters stand on deep foundation piles. Some piles are bored and filled with concrete; others are driven into the ground by hammers like the one in Fig 6.10 – every blow turns the hammer's potential energy into kinetic energy, and then into the work of pushing the pile down (plus heat and that loud bang of sound).
- 🧪 Energy Skate Park (PhET simulation) PhET, University of Colorado Boulder
The sim named in your textbook: watch PE and KE trade places while the total stays the same. - 🧪 Energy Skate Park: Basics (PhET simulation) PhET, University of Colorado Boulder
A simpler version of the skate park - great first try with pie charts and bar graphs. - 🧪 Pendulum Lab (PhET simulation) PhET, University of Colorado Boulder
A swinging bob changes PE into KE and back again - turn on the energy graph to see it. - 🧪 Roller Coaster Model The Physics Classroom
Design a coaster track and watch energy bar charts; switch friction on to see energy 'lost' as heat. - 📄 Mechanical Energy The Physics Classroom
Mechanical energy = PE + KE, and when it stays constant. - 📄 The law of conservation of energy: A simple introduction Explain that Stuff
Energy is never made or destroyed, only changed - explained with everyday examples.
4. Check yourself
- Energy transformation: machines change energy from one form to another (motor: electrical → mechanical; petrol car: chemical → kinetic; iron box: electrical → heat; solar cell: light → electrical).
- Balloon car: blowing stretches the rubber → potential energy (configuration) → kinetic energy → finally heat through friction.
- Pile driver (1000 kg, 10 m): at the top Ep = 98 000 J, Ek = 0; at the ground Ep = 0, v = 14 m/s, Ek = 98 000 J. Total stays 98 000 J.
- Law of conservation of energy: energy can neither be created nor destroyed, only changed from one form to another.
- Work and energy: both scalars, same unit (joule); energy is used up in doing work.