Knowledge Organiser: Kinetic Energy
Key Terms
- Kinetic energy: energy stored in a moving object
- Mass: amount of matter, in kg
- Velocity: speed with direction, in m/s
- Work done and KE: work done = change in KE
Key Equation
- E_k = ½mv²
- Rearranged: m = 2E_k / v²
- Rearranged: v = √(2E_k / m)
- Units: J, kg, m/s
Key Facts
- KE ∝ mass (directly proportional)
- KE ∝ velocity² (squared relationship!)
- Double speed = 4× KE; triple speed = 9× KE
- KE transfers to thermal when object stops
Exam Tips
- Never forget the ½ or the squared on v
- Mass in kg, velocity in m/s — convert first
- Square root the result when finding v
- KE = GPE for falling objects problems
Common Mistakes
- Forgetting the ½: Eₖ = ½mv² — students often write mv², losing all marks on calculation questions
- Not squaring velocity: The v² means doubling speed quadruples KE — remember to square v before multiplying
- Wrong units: Mass must be in kg and velocity in m/s — convert before substituting
- Rearranging errors: To find v, divide by ½m first then square root — don't skip steps
- Confusing KE with momentum: KE = ½mv², momentum = mv — they are different quantities
Memory Aid
- Remember E_k = ½mv² with this sequence: "Half My Velocity Squared"
- Half = the ½ | My = m (mass) | Velocity = v | Squared = the ² superscript
- For the v² effect, think of road safety: "Double the speed, four times the danger." This locks in the squared relationship without even needing the formula.