Theme A — Space, Time and Motion
A.3.1 Principle of Conservation of Energy — IB Physics HL Revision Notes & Topical Questions
5 min read 11 parts Lesson 32 of 63 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
A.3.1 Principle of Conservation of Energy — IB PHYSICS SL notes: State the principle of conservation of energy and use it to account for energy transfers in a closed system.Conservation of energy — energy cannot be created or destroyed; it can only be transferred from one form to…
- Equilibrium
- Every real device obeys it
- Kinetic energy
- Gravitational potential energy
- Elastic potential energy
- Mechanical energy
Part 1 of 9The principle
The principle
Conservation of energy
- Conservation of energy energy cannot be created or destroyed;
- it can only be transferred from one form to another.
Closed system
- Closed system the total energy stays constant, although the amounts in each form may change.
System
- System an object or group of objects chosen to focus on what is relevant.
Equilibrium
- Equilibrium when nothing changes in a system, nothing happens; changes involve energy transfers.
Every real device obeys it
- Every real device obeys it a kettle does not make energy, it shares the electrical energy between the water and the surroundings.
Part 2 of 9Energy and its stores
1Energy
- Energy a measure of the capacity of a system to bring about change; it is a scalar in joules.
2Joule
- Joule the energy transferred when a force of 1 N moves its point of application 1 m in the direction of the force.
3Kinetic energy
- Kinetic energy it belongs to moving objects.
4Gravitational potential energy
- Gravitational potential energy it depends on position in a gravitational field.
5Elastic potential energy
- Elastic potential energy it is stored in stretched or compressed materials.
6Mechanical energy
- Mechanical energy kinetic, gravitational and elastic potential energy together.
7Thermal (internal) energy
- Thermal (internal) energy the random kinetic and potential energy of particles.
8Other stores
- Other stores chemical, nuclear, electrical and electromagnetic radiation energy.
Part 3 of 9Transfers between a system and its surroundings
Transfers between a system and its surroundings
Work
- Work a force acts through a displacement, or charge moves through a potential difference.
Heating
- Heating thermal energy flows because of a temperature difference, by conduction, convection or radiation.
Radiation
- Radiation electromagnetic waves, such as light from the Sun, carry energy; sound waves do too.
Method
- Method draw a boundary around the system and list every transfer crossing it.
Part 4 of 9Energy dissipation
1No transfer is 100% efficient
- No transfer is 100% efficient some energy is dissipated to the surroundings.
2Wasted energy
- Wasted energy it usually ends up as thermal energy that is hard to use again.
3Kettle
- Kettle thermal energy passes from the element to the water (useful), and to the casing and the surrounding air (wasted).
4Not vanished
- Not vanished wasted energy has spread out, not disappeared.
Part 5 of 9Applications
1Falling object in a vacuum
- Falling object in a vacuum gravitational potential energy becomes kinetic energy.
2Horizontal mass on a spring
- Horizontal mass on a spring elastic potential energy becomes kinetic energy.
3Battery
- Battery chemical energy becomes electrical energy.
4Car
- Car chemical energy in the fuel becomes kinetic energy.
5Trampoline
- Trampoline energy moves from elastic potential to kinetic to gravitational potential.
6Rough incline
- Rough incline loss in kinetic energy = gain in gravitational potential energy + work done against friction.
Part 6 of 9Energy bookkeeping
Balance
- ΔEtotal = Ein − Eout, which is zero for a closed system.
Ball falling in air
- Ball falling in air gravitational potential energy falls, kinetic energy rises by less, and air resistance warms the air and ball.
Missing term
- Missing term if energy seems to go missing, a transfer has been overlooked.
One-line habit
- One-line habit write energy in = useful energy out + wasted energy and fill in each term.
Experimental check
- Experimental check a trolley on a ramp with light gates shows a small kinetic energy shortfall that measures the energy dissipated by friction.
Part 7 of 9Vertical spring
Position A (top)
- Position A (top) some elastic potential energy, kinetic energy zero and gravitational potential energy maximum.
Position B (equilibrium)
- Position B (equilibrium) kinetic energy is maximum, with some elastic and gravitational potential energy.
Position C (bottom)
- Position C (bottom) elastic potential energy is maximum, kinetic energy zero and gravitational potential energy minimum.
Total
- Total it remains constant throughout.
Horizontal spring
- Horizontal spring gravitational potential energy does not change, so only kinetic and elastic energy exchange.
Part 8 of 9Mechanical and total energy
Mechanical energy
- Mechanical energy it is conserved only when no friction or drag acts.
Total energy
- Total energy it includes thermal energy and is always conserved.
Link to other topics
- Link to other topics the principle becomes the first law of thermodynamics and, with E = mc2, combines mass and energy.
Part 9 of 9More from the specification
More from the specification
Total mechanical energy invariance
- Total mechanical energy invariance evaluating energy transformations between kinetic and potential forms provides an empirical means to verify conservation.
Conservation of energy
- Conservation of energy energy cannot be created or destroyed, only transferred between stores, so total energy of an isolated system is constant
Sankey diagram
- Sankey diagram an arrow whose width is proportional to energy, showing useful output and wasted energy
Power
- Power the rate of energy transfer, equal to work divided by time, as for a motor lifting a mass to a height
Energy density
- Energy density energy released per unit mass or volume of a fuel, used to compare energy sources
Density
- Mass per unit volume.
Component
- Part of a vector along one axis.
Distance
- Total length of path travelled, a scalar.
Energy density
- The energy available per unit mass or area of a resource.
Sankey diagram
- Diagram where arrow width shows energy amount.
Resultant force
- Another name for net force.
Final speed
- Speed at the end, v
W = Fs
What the symbols mean: W = work done = energy transferred (J) · F = force (N) · d, s or x = distance moved in the direction of the force (m)
W
Fs = 25.6 × 20 = 512 J
What the symbols mean: W = work done = energy transferred (J) · F = force (N) · d, s or x = distance moved in the direction of the force (m)
Key terms
| Term | Meaning |
|---|---|
| Conservation of energy | Energy cannot be created or destroyed, only transferred or transformed |
| System | An object or group of objects chosen for study |
| Mechanical energy | Sum of kinetic, gravitational potential and elastic potential energy |
| Dissipated energy | Energy spread to the surroundings, usually as thermal energy |
| Useful energy | Energy transferred in the way that is wanted |
| Closed system | System that exchanges no energy with its surroundings |
Avoid these mistakes
1
Saying energy is lost — it is transferred to the surroundings, usually as thermal energy.
2
Assuming mechanical energy is always conserved — only without friction or drag.
3
Counting the wasted energy as destroyed — total energy is conserved.
4
Forgetting a transfer when the totals do not match — look for work, heating or radiation.
5
Treating energy as a vector — it is a scalar.
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