PHYSICS · Stage 7 · Chapter 1: Energy
Physics 1.8 Chapter 1 Review: Energy
5 min read 5 parts Lesson 8 of 8
Lesson summary
1.8 Chapter 1 Review: Energy — Alhussan International Academy — Physics (Stages 7–9) notes: Revise energy stores, transfers, gravitational potential and kinetic energy, elastic energy and investigation skills.Stores — energy is measured in joules and held in chemical, kinetic, gr…
- Conservation
- Dissipation
- Efficiency
- Trampoline
- Stretched objects
- Independent variable
Part 1 of 5Stores, pathways and conservation
- Storesenergy is measured in joules and held in chemical, kinetic, gravitational potential, elastic potential, thermal and nuclear stores.
- Pathwaysenergy moves by mechanical, electrical and heating pathways, and by waves such as light and sound.
- Conservationenergy is never created or destroyed.
- Dissipationin every transfer some energy is dissipated as thermal energy, so the useful output is less than the input.
- Efficiency useful output ÷ total input × 100%.
Part 2 of 5Gravitational potential and kinetic energy
1GPE1 point
— the higher an object is above the ground and the greater its mass, the more GPE it has: GPE = m × g × h.
- To order objects by GPE, compare mass and height, so Josie on the top diving board has more GPE than a child on a low board.
2Falling2 points
— GPE decreases and KE increases.
- Just before hitting the mat, KE is at a maximum.
- At the top of a jump, KE is zero and GPE is greatest.
3Trampoline1 point
— at the top of a bounce energy is mostly gravitational potential, and at the lowest point the trampoline is stretched and has elastic potential energy.
- As a person leaves the mat all the energy is kinetic.
Part 3 of 5Elastic energy and bouncing
- Stretched objects — a stretched spring has elastic potential energy.
- Bouncing — a ball never bounces to its original height because some energy is dissipated by sound and heating.
Part 4 of 5Pendulum and investigation skills
- InvestigationChinonye times 10 swings for different children on a swing and calculates the periods, finding that a longer swing has a longer period.
- Independent variablethe length of the swing.
- Dependent variablethe time for 10 swings.
- Controlsthe angle and number of swings.
- Methodrepeat the timings, find the mean and use a table with headings and units.
- Improvementuse video to time the swings.
| Skill | Reminder |
|---|---|
| Calculating period | Total time ÷ number of swings |
| Efficiency | Useful ÷ total × 100% |
| GPE | m × g × h |
Part 5 of 5Checking answers
- Storescheck which store increases and which decreases.
- Falling ballGPE decreases and KE increases, but at the top of a bounce KE is zero.
- Unitsenergy in J, force in N, height in m.
- Efficiencyit has no units but can be written as a percentage.
- Graphsread them carefully and note whether a line is straight or curved.
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