S4.9.1 For the adult
Calculating energy stores
A car drives at 10 m/s and then at 20 m/s. What happens to its kinetic energy?
What this chapter teaches
Kinetic energy is ½ × m × v², and the speed is squared. Gravitational potential energy is m × g × h. In a fall without air resistance the two add up to a constant total, so the speed after a fall depends on the height and not on the mass.
Three questions to ask
There is no one right wording. Listen for the idea.
- A car goes twice as fast. How much more kinetic energy does it have, and why?
- Why does a heavy stone not land faster than a light one?
- What must you change before using the kinetic energy formula with a speed in km/h?
After the chapter, the learner can
- Calculate kinetic energy and gravitational potential energy
- Use energy conservation to find the speed of a falling object
What they copy into their notebook
Ek = ½ × m × v². Ep = m × g × h, with g = 9.8 N/kg. A falling thing turns Ep into Ek. Ignoring air, v² = 2 × g × h, and the mass cancels.