1. Balance and Motion

2. Investigation 1: Balance

3. arch A curved shape.

4. balance To stay in a position without being held.

5. balance point The place on which an object balances.

6. clothespin A clip of wood or plastic for fastening clothes on a clothesline.

7. counterweight Something that helps to balance an object.

8. crayfish A freshwater shellfish.

9. mobile A system of balance beams and objects.

10. object Anything that can be seen or touched; a thing.

11. position The place where a person or thing is.

12. stable Steady; not falling over.

13. system A set of objects that are related in some way and can be isolated for study; a group of things or parts that form a whole.

14. triangle A three-sided shape.

15. unstable When something is not steady and falls over.

16. weight How heavy something is.

17. wire A bendable metallic strand or rod.

18. Investigation 2: Spinners

19. air resistance The force of air pushing on something.

20. axis A straight line around which something rotates.

21. disk An object that is a circle in only one direction and can fall over; a disk can be a wheel.

22. knot To firmly tie two pieces of material together.

23. motion The act of moving. When something moves.

24. rotate To turn in circles a lot of times; to spin.

25. shaft Something that acts as an axis.

26. spin To turn by turning around an axis. To turn in circles a lot of times; to rotate.

27. swirl To spin or twist around and around.

28. top A toy that spins.

29. twirl To spin in the air.

30. twirler A flying spinner.

31. twist To wind or turn something around.

32. whirl To move or turn around quickly or suddenly.

33. wing The moveable appendages that birds and other animals use to fly.

34. zoomer A toy made from a plastic disk and a piece of string; it spins around when tension is released from the twisted string.

35. Investigation 3: Rollers

36. axle A rod or shaft to which wheels can be attached.

37. loop An opening that is made by curving a piece of material into a circle.

38. ramp An object that has a slope.

39. runway A path over which something moves or lands.

40. slope A surface that is higher on one end.

41. sphere An object that is round in all directions and rolls in all directions.

42. spiral To move in a circular motion around a fixed center point.

43. wheel An object that is a circle in only one direction and can fall over; a wheel is a disk.

44. Science Stories

45. force A push or a pull.

46. gravity A force that pulls things toward the Earth.

47. pitch How high or low a sound is.

48. roll To move by turning over and over. When a wheel goes around on its edge.

49. stable position Steady, not falling over.

50. vibration A fast back and forth motion. Vibration makes sound.

51. volume How loud or soft a sound is.