Physics riddles

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Across
  1. 1. I’m the time it takes for half to decay, A measure in physics that won’t sway. Used in dating ancient remains, What am I, with my constant gains? (4,4)
  2. 4. I'm the rate of work, the pace of flow, In watts or horsepower, my values show. From generators to engines, I'm the call, What am I, that drives them all? (5)
  3. 7. In circuits I act against the flow, Electrons struggle, and heat will show. Ohm's law defines me, as you might know, What am I, where currents slow? (10)
  4. 11. I bend the path of light or sound, In glass and water I am found. My index shows how fast they go, What am I, causing the wave to slow? (10)
  5. 12. I flow in circuits, through wires I race, Electrons moving at a rapid pace. Coulomb is my unit, as you might surmise, What am I, in electric guise? (6)
  6. 16. I’m the reason why helium can soar, While lead sinks low, heavy and more. Mass per unit volume, I'm the key, What am I, in physics' decree? (7)
  7. 17. I resist the change, whether fast or slow, Newton's First declares it's so. Objects at rest or in motion's flow, What am I, that keeps this status quo? (7)
  8. 18. When you lift a box or climb a hill, I measure the effort, the strength, the will. Force times distance is my name, In joules or calories, I'm always the same. (4,4)
  9. 20. I am the push or pull, strong or weak, Behind every motion, I'm what you seek. Newton described me in his famous laws, What am I, the hidden cause? (5)
Down
  1. 2. I’m the wave's height from peak to the middle, Energy measured, so answer my riddle. The taller I am, the stronger the wave, What am I, that surfers crave? (9)
  2. 3. I am the measure of matter's span, Inertia depends on me, understand? Kilograms or grams, will quantify, on a balance, and that's no lie (4)
  3. 5. I'm the energy of motion, dynamic and fleet, When objects move, I'm what they greet. From speeding cars to winds that blow, What am I, in motion's flow? (7)
  4. 6. I'm the displacement divided by time, With units like meters per second to rhyme. Speed is my partner, yet different we are, What am I, moving near and far? (8)
  5. 8. At rest or in motion, I'm force's kin, a potential to move is where I begin. Once in motion, kinetic I become, What am I, in physics' hum? (6)
  6. 9. I curve space-time and make you fall, Holding planets, big and small. Newton then Einstein told my tale, What am I, where masses prevail? (7)
  7. 10. When objects collide and then they split, I measure how they transfer hit. Mass and velocity are my friends, In closed systems, my total never ends. (8)
  8. 13. How do we measure velocity's climb? For changes in motion, I'm the prime. Meters per second squared, I portray, What am I, in swift display? (12)
  9. 14. I'm the charge's flow, the lively parade, Through wires and circuits, I'm relayed. Ampere is my unit, the electric flow, What am I then, surely you know? (7)
  10. 15. I’m the time it takes for one complete round, A cycle in motion, in waves I’m found. From crest to crest or trough to trough, What am I, is that so tough? (6)
  11. 19. I'm the measure of effectiveness, the task's true score, In percentage or decimal, I show what's more. Useful Output by input, I calculate, If you want to save money then I am your mate (10)