1 Energy Stores and their Description
Chemical
Energy in bonds between atoms (Food, Batteries, Fuel).
Kinetic
Stored when an object is in motion.
Gravitational
Stored due to an object's position in a gravitational field.
Elastic Potential
Stored when an object is stretched or compressed.
Thermal
Stored as an object's temperature increases.
Magnetic
Stored in magnetic fields between poles.
Nuclear
Energy stored in the nucleus of an atom.
Electrostatic
Stored between charged objects.
Energy Pathways
Heat
Mechanical
Radiation
Electrical
Task: Describe the Pathways
2 Worked Examples of GPE, KE and Ep
GPE: Finding Height
A pole-vaulter of mass 70kg has 2744J of GPE. What is the height of the bar?
1. Formula: h = GPE / (m × g)
2. Substitute: h = 2744 / (70 × 9.8)
3. Calculate: h = 2744 / 686
Answer: h = 4m
KE: Standard Calculation
Calculate the KE of a boulder of mass 6kg rolling down a hill with speed 5m/s.
1. Formula: KE = ½ × m × v²
2. Substitute: KE = 0.5 × 6 × 5²
3. Calculate: KE = 3 × 25
Answer: KE = 75J
Ep: Spring Constant
A rubber band (k=10N/m) stretches by 0.04m. Calculate the energy stored.
1. Formula: Ep = ½ × k × e²
2. Substitute: Ep = 0.5 × 10 × 0.04²
3. Calculate: Ep = 5 × 0.0016
Answer: Ep = 0.008J
3 GPE, KE and Ep Calculator
GPE: 0 J
KE: 0 J
Ep: 0 J
Progress Check
Calculate the missing variables. Pay attention to units (g to kg, cm to m)! (g = 9.8)
GPE Challenges (Height & Mass)
1. Find GPE: Book of mass 450g at 80cm. (Units!)
2. Find Mass: Rock with 200J GPE at a height of 16m.
3. Find Height: Lift transported 4 people (60kg each) with 28,224J GPE.
4. Find Height: Suitcase of 20kg at 50cm lifted to new height gaining 100J.
KE Challenges (Mass & Speed)
1. Find Mass: Object with 800J KE and speed of 5m/s.
2. Find Speed: Runner of 50kg with kinetic energy of 900J.
3. Find Speed: Helicopter (1500kg) with KE of 1,200,000J.
4. Find Speed: Car (1200kg) travelling at 30m/s. Calculate KE.
Elastic Mastery (k & Extension)
1. Find Spring Constant (k): Stretches 0.12m with 0.00288J.
2. Find k: Bow pulled 40cm (Units!) storing 24J energy.
3. Find Extension: Bungee cord (k=4.5) stores 0.5625J.
4. Find Compression: Machine (k=450) stores 12.96J.
4 Conservation of Energy
The Law of Conservation
"Energy cannot be created or destroyed, but transferred from one form to another."
Top of Hill: Maximum GPE, Zero KE.
Descending: Speed increases, so KE increases while GPE decreases.
Losses: Real systems lose energy as Thermal and Sound due to friction and air resistance.
Bottom: Maximum KE, Zero GPE.
If no energy is lost:
KE gained = GPE lost
½mv² = mgh → v = √(2gh)
Roller Coaster Simulation
Conservation Mastery Check
Calculate final velocity using v = √(2gh) (g = 9.81 N/kg).
Task 1
Ball (0.4kg) rolls down a hill of height 12m. Final velocity?
Task 2
Mountain goat (50kg) from cliff height 400m. Final speed?
Task 3
Roller coaster (500kg) descends 120m height. Speed?
Task 4
Raindrop of 0.03g (convert to kg!) falls 750m. Final speed?