Overview
This checkpoint covers key concepts in energy, including definitions, forms, transformations, the law of conservation, calculation of potential and kinetic energy, and practical energy conversion examples.
Basic Energy Concepts
- Energy is the ability to do work or cause change.
- The SI unit of energy is the Joule (J).
Types of Energy
- Active energy (kinetic energy) is the energy of motion.
- Potential energy is stored energy due to position or condition.
- Active energy examples: running cheetah, moving car, flowing water.
- Potential energy examples: stretched bow, water behind dam, raised object.
Energy Transformation
- Energy transformation is the process of converting one form of energy into another.
Energy Transformation Diagrams
- Rabbit jumping: potential energy → kinetic energy
- Washing machine: electrical energy → mechanical (kinetic) + heat + sound energy
- Eating food and running: chemical energy → kinetic energy
- Turning on Bunsen burner: chemical energy → heat + light energy
Law of Conservation of Energy
- Energy cannot be created or destroyed, only transformed from one form to another.
Gravitational Potential Energy Calculations
- Ep = mgh, where g = 10 m/s².
- (a) Ep = 84 kg × 10 × 13.4 m = 11,256 J
- (b) Ep = 147 kg × 10 × 20.9 m = 30,723 J
- (c) Jug A: Ep = 0.5 kg × 10 × 11.2 = 56 J; Jug B: Ep = 0.302 kg × 10 × 14.4 = 43.488 J; Jug A has more Ep.
Kinetic Energy Calculations
- Ek = ½mv².
- (d) Lion: Ek = 0.5 × 54 × 30² = 24,300 J
- (e) Truck: Ek = 0.5 × 403 × 80² = 1,289,600 J
- (f) Kea: Ek = 0.5 × 0.15 × 42² = 132.3 J; Kākāpo: Ek = 0.5 × 0.302 × 56² = 473.12 J; Kākāpo has more Ek.
Energy Conversion in Appliances
- Hair dryer: Heat = 250 J; Useful = 250 J; Wasteful = 150 J
- TV: Electrical = 2650 J; Useful = 1850 J; Wasteful = 800 J
- Washing machine: Light = 200 J; Kinetic = 6300 J; Wasteful = 1700 J
Key Terms & Definitions
- Energy — ability to do work or cause change.
- Joule (J) — SI unit of energy.
- Active (Kinetic) Energy — energy of moving objects.
- Potential Energy — stored energy based on position or condition.
- Energy Transformation — conversion from one energy form to another.
- Law of Conservation of Energy — energy is neither created nor destroyed.
Action Items / Next Steps
- Review formulas for Ep and Ek.
- Complete any outstanding calculations and fill in appliance energy tables if not finished.
- Prepare for further discussions on energy efficiency.