1. friction

2. friction
surface resistance to relative motion, as of a body sliding or rolling.
the rubbing of the surface of one body against that of another.

3. force

4. force
a push or pull on an object.

5. speed

6. speed
relative rapidity in moving, going, etc.; rate of motion or progress.

7. electromagnetic wave

8. electromagnetic wave
a wave produced by the acceleration of an electric charge and spread by the periodic variation of intensities of electric and magnetic fields.
a transverse wave that an travel through empty space and through matter.

9. Global Positioning System (GPS)

10. Global Positioning System (GPS)
a navigational system using satellite signals to fix the location of a receiver on or above the earth's surface.
a global system of U.S. navigational satellites developed to provide precise  positional and velocity  data and global time synchronization for air, sea, and land travel.

11. electric circuit

12. electric circuit
is a closed, or complete path in which electrons (electric current) from a voltage or current source flow. 
a circular journey or one beginning and ending at the same place.

13. electric current (electricity)

14. electric current (electricity)
a movement of electrically charge particles accompanied by such observable effects as the production of heat, light, of a magnetic field, or of chemical transformations.

15. electric resistance

16. electric resistance
a measure of how difficult it is for an electric current to flow in a material.
Resistance is measured in ohms.

17. voltage

18. voltage
electromotive force or potential difference expressed in volts.

19. Newton

20. Newton
the standard unit of force in the International System of Units (SI), equal to the force that produces an acceleration of one meter per second per second on a mass of one kilogram.

21. gravity

22. gravity
the force of attraction by which terrestrial bodies tend to fall toward the center of the earth.
heaviness or weight.

23. centripetal force

24. centripetal force
in circular motion, a force that acts perpendicular to the direction of motion, toward the center of the curve.

25. align

26. align
to arrange in a straight line; adjust according  to a line.

27. magnet

28. magnet
a body, as a piece of iron or steel, that possesses the property of attracting certain substances, as iron.
an object that attracts iron.

29. electric motor

30. electric motor
a device that uses an electric current to produce motion.

31. electromagnet

32. electromagnet
a magnet created by wrapping a current-carrying wire around a ferromagnetic core.

33. dimension

34. dimension
any of a set of basic kinds of quantity, as mass, length, and time, in terms of which all other kinds of quantity can be expressed.

35. displacement

36. displacement the displacing in space of one mass by another.
the weight or the volume of fluid displaced by a floating or submerged body.

37. acceleration

38. acceleration
increase of speed or velocity.
a change in velocity.

39. inertia

40. inertia
a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force.

41. motion

42. motion
the action or process of moving or of changing place or position; movement.

43. position

44. position
condition with reference to place; location;  situation.

45. reference point

46. reference point
something that is used to judge or understand something else .

47. air resistance

48. air resistance
the opposition of the atmosphere to forward movement.

49. relative

50. relative
something having, or standing in, some  relation or connection to something else.

51. specify

52. specify
to mention or name specifically or definitely; state in detail.

53. horizontal

54. horizontal at right angles to the vertical; parallel to level ground.
near, on, or parallel to the horizon.

55. momentum

56. momentum
force or speed of movement; impetus, as of a physical object or course of events.
strength or force gained by motion or by a series of events.

57. velocity

58. velocity quickness of motion.
the rate of change of position along a straight line with respect to time.

59. vertical

60. vertical
being in a position or direction perpendicular to the plane of the horizon; upright; plumb.