Energy exists in many forms — kinetic (motion), potential (stored, due to position or state), thermal, chemical, electrical — and the law of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another or transferred between objects. Work, in physics, is done when a force causes movement over a distance (W = F × d); doing work on an object transfers energy to it. The first law of thermodynamics extends conservation of energy to heat and internal energy specifically, while the second law introduces the concept of entropy — the tendency of energy to disperse and systems to become more disordered over time, which is why some energy is always 'lost' as unusable heat in real energy transformations.
Example
A car engine converts the chemical potential energy stored in fuel into kinetic energy (motion), but not with perfect efficiency — some energy is unavoidably converted into heat through friction and engine inefficiency, consistent with the second law of thermodynamics, which is why real engines are never 100% efficient no matter how well-designed.
Key terms
Conservation of energy:
The principle that energy cannot be created or destroyed, only transformed or transferred.
Entropy:
A measure of disorder in a system, which tends to increase over time.
Questions
1. The law of conservation of energy states that energy:
Cannot be created or destroyed, only transformed
Can be freely created from nothing
Always disappears completely over time
Has no connection to any physical process
2. Kinetic energy is energy due to:
Motion
Position only, with no motion involved
Temperature alone
Chemical composition only
3. Work in physics is done when:
A force causes movement over a distance
Nothing moves at all
A force is applied with no resulting movement
Energy disappears completely
4. The formula for work is:
W = F × d
W = F + d
W = F − d
W = F ÷ d always equals zero
5. Entropy is a measure of:
Disorder in a system
Total mass only
Colour only
Something unrelated to energy or disorder
6. According to the second law of thermodynamics, entropy in a system tends to:
Increase over time
Always decrease over time
Remain completely fixed forever
Have no relationship to time at all
7. In a car engine, some chemical energy from fuel becomes:
Heat, due to friction and inefficiency
Entirely kinetic energy with no loss
Completely destroyed and gone
Something with no connection to energy transformation
8. Why is it more accurate to say energy is "transformed" rather than "used up" when a car burns fuel to move?
The total energy is conserved — chemical energy is converted into kinetic energy and heat, not destroyed
Energy is genuinely destroyed and disappears completely when fuel is burned
Burning fuel creates entirely new energy that did not exist before
The law of conservation of energy has no application to a car burning fuel
9. Why does lifting a heavy box straight up require doing work, using the formula W = F × d?
A force (against gravity) is applied and the box moves a distance, satisfying the definition of work being done
Lifting a box never actually involves any force or distance, so no work is done
Work is only ever done when an object moves horizontally, never vertically
The formula W = F × d has no application to lifting a heavy object
10. Why might a roller coaster car have maximum kinetic energy at the bottom of a hill and maximum potential energy at the top?
Height above the ground affects gravitational potential energy, and this is converted to kinetic energy as the car descends and speeds up
A roller coaster car's energy has no connection to its height or speed at any point on the track
Potential and kinetic energy are always at their maximum at exactly the same point on a roller coaster
The car's energy remains completely constant and unconverted throughout the entire ride
11. Why does no real machine or engine achieve 100% energy efficiency, given the second law of thermodynamics?
Some energy is always dispersed as unusable heat due to friction and other inefficiencies, consistent with entropy tending to increase
Modern engineering has already created machines that achieve perfect, 100% energy efficiency
The second law of thermodynamics has no real connection to why machines lose some energy as heat
Energy efficiency in real machines has no relationship to entropy or the laws of thermodynamics
12. Why might a swinging pendulum eventually come to rest, even though energy is technically conserved throughout its motion?
Air resistance and friction at the pivot gradually convert the pendulum's kinetic and potential energy into heat, which disperses rather than disappearing entirely
A pendulum swinging in a real environment never actually loses energy to any external factor and would swing forever
Conservation of energy is violated whenever a pendulum eventually comes to rest
The pendulum coming to rest has no connection to energy transformation or the presence of friction
13. Why might comparing the energy input and useful energy output of two different light globes (like an incandescent bulb versus an LED) reveal a significant difference in their efficiency?
Different technologies convert electrical energy into light with varying proportions lost as heat, so measuring useful output against total input reveals real efficiency differences
All light globes, regardless of technology, always convert electrical energy into light with exactly identical efficiency
Comparing energy input and output has no bearing on evaluating the relative efficiency of different light globe technologies
Efficiency differences between light globe technologies are always purely coincidental with no real underlying cause
14. Why might rubbing your hands together to warm them up be considered an example of work being converted into thermal energy?
The force and movement (friction) between your hands does work, and that work is converted into heat due to friction
Rubbing your hands together involves no force or movement, so no work is actually being done
Friction between two surfaces never actually produces any heat or thermal energy
Work and thermal energy are always completely unrelated physical concepts
15. Why might a perpetual motion machine (one that runs forever with no energy input) be considered impossible according to the laws of thermodynamics?
Any real machine loses some energy to friction and heat (entropy), meaning it would eventually run out of usable energy without an external energy input
Perpetual motion machines are entirely possible and have already been successfully built and demonstrated
The laws of thermodynamics have no bearing on whether a perpetual motion machine could theoretically work
Energy losses to friction and heat never actually occur in any real mechanical system
16. Why might the total entropy of an isolated system (like the universe as a whole) be expected to increase over time, even though entropy can locally decrease in a specific smaller system?
A localised decrease in entropy (like a fridge cooling food) always requires energy input that increases entropy elsewhere by a greater amount, so the overall total still increases
Entropy in any isolated system, no matter its scale, always remains exactly constant over time with no change
A decrease in entropy within any smaller part of a system always means overall total entropy is also decreasing
The scale of a system (local versus universal) has no bearing on how the second law of thermodynamics applies to it
17. Why might understanding energy conservation be essential for analysing a complex system (like a power station) where energy passes through many different forms before reaching its final use?
Conservation of energy lets you track and account for energy through every transformation stage, helping identify where losses occur and how efficiency could be improved
Energy conservation principles only ever apply to very simple systems, never anything as complex as a power station
Tracking energy through multiple transformation stages provides no useful information about a system's efficiency
A power station's energy transformations occur with no connection to the law of conservation of energy
18. Why might renewable energy technologies (like solar panels) still be subject to the same fundamental efficiency limits described by the second law of thermodynamics, despite not burning fuel?
Any energy conversion process, including converting sunlight into electricity, involves some unavoidable energy loss as heat, consistent with entropy increasing in any real transformation
Renewable energy technologies are somehow completely exempt from the laws of thermodynamics that apply to other energy systems
Solar panels achieve perfect, 100% conversion efficiency with absolutely no energy loss of any kind
The second law of thermodynamics only applies to systems that burn fuel, never to any other type of energy conversion
19. Why might understanding the distinction between energy being "conserved" overall and energy becoming "less usable" (higher entropy) be important for evaluating claims about energy technology?
A technology can conserve total energy perfectly while still losing significant usable energy to heat, so evaluating usefulness requires looking beyond simple conservation to actual efficiency
Total energy conservation and usable energy are always exactly the same thing with no meaningful distinction
Any technology that conserves total energy is automatically considered maximally efficient with no further evaluation needed
This distinction has no genuine relevance to evaluating real energy technologies or their claims
20. Why might a hydroelectric dam be considered a relatively efficient way to convert one form of energy into electricity, compared to some other energy conversion processes?
Converting gravitational potential energy (falling water) directly into kinetic energy and then electrical energy involves fewer conversion steps and therefore fewer opportunities for energy loss than more indirect processes
All methods of generating electricity are always exactly equally efficient regardless of how many energy conversion steps are involved
Hydroelectric dams actually lose more energy to heat and friction than almost any other electricity generation method
The number of energy conversion steps involved in generating electricity has no bearing on overall efficiency
21. Understanding energy, work and thermodynamics mainly helps you to:
Analyse how energy transforms and transfers between forms while accounting for unavoidable losses to entropy
Assume energy can be freely created or completely destroyed in physical processes
Ignore the connection between doing work and transferring energy to an object
Treat perfect, 100% energy efficiency as achievable in any real-world machine
Answer key (parent copy)
1. Cannot be created or destroyed, only transformed
2. Motion
3. A force causes movement over a distance
4. W = F × d
5. Disorder in a system
6. Increase over time
7. Heat, due to friction and inefficiency
8. The total energy is conserved — chemical energy is converted into kinetic energy and heat, not destroyed
9. A force (against gravity) is applied and the box moves a distance, satisfying the definition of work being done
10. Height above the ground affects gravitational potential energy, and this is converted to kinetic energy as the car descends and speeds up
11. Some energy is always dispersed as unusable heat due to friction and other inefficiencies, consistent with entropy tending to increase
12. Air resistance and friction at the pivot gradually convert the pendulum's kinetic and potential energy into heat, which disperses rather than disappearing entirely
13. Different technologies convert electrical energy into light with varying proportions lost as heat, so measuring useful output against total input reveals real efficiency differences
14. The force and movement (friction) between your hands does work, and that work is converted into heat due to friction
15. Any real machine loses some energy to friction and heat (entropy), meaning it would eventually run out of usable energy without an external energy input
16. A localised decrease in entropy (like a fridge cooling food) always requires energy input that increases entropy elsewhere by a greater amount, so the overall total still increases
17. Conservation of energy lets you track and account for energy through every transformation stage, helping identify where losses occur and how efficiency could be improved
18. Any energy conversion process, including converting sunlight into electricity, involves some unavoidable energy loss as heat, consistent with entropy increasing in any real transformation
19. A technology can conserve total energy perfectly while still losing significant usable energy to heat, so evaluating usefulness requires looking beyond simple conservation to actual efficiency
20. Converting gravitational potential energy (falling water) directly into kinetic energy and then electrical energy involves fewer conversion steps and therefore fewer opportunities for energy loss than more indirect processes
21. Analyse how energy transforms and transfers between forms while accounting for unavoidable losses to entropy