Energy changes
Question 1 of 5
Five questions done!
0 / 20facts practised
0getting stronger
20 essential facts
Progress saves in this browser.
Five questions at a time. Correct answers earn 10 points. No timer, no lost lives.
Missed facts return after two other answers, or in your next round. Come back tomorrow for a spaced review.
Correct reviews grow further apart: 1, 3, 7, 14, then 30 days. Extra practice is always available. A fact is “getting stronger” after correct reviews on different days.
Your progress stays in this browser on this device. Clearing browser data removes it.