Newton's Laws

1. What is force?

A push or pull that can change an object’s motion or cause distortion.

2. Is force a scalar or vector?

A vector.

3. What are everyday examples of force?

Pushing, shoving, lifting, pulling, and dragging.

4. What is weight?

The force of gravity acting on an object.

5. What symbol represents weight?

(W).

6. What two things does weight depend on?

The object’s mass and its gravitational environment.

7. What is friction?

A force that resists relative motion between objects or substances in contact.

8. What is static friction?

Friction between objects that have no relative motion between them.

9. What is an example of static friction?

Shoes gripping the ground while walking.

10. What is kinetic friction?

Friction that acts when two contacting substances move relative to each other.

11. What is an example of kinetic friction?

A tire skidding on pavement.

12. What is Newton’s First Law?

An object stays at rest or moves with constant velocity unless acted on by a net external force.

13. What is an external force?

A force caused by an agent outside the object or system.

14. What is an example of an external force?

Earth’s gravitational pull on an object.

15. What is net force?

The vector sum of all external forces acting on an object.

16. What happens when equal forces act in opposite directions?

They cancel, producing zero net force.

17. How do you find net force when forces act in the same direction?

Add their magnitudes.

18. How do you find net force when forces act in different directions?

Add the force vectors, accounting for their directions.

19. When is a force required to change an object’s motion?

When its velocity changes in speed, direction, or both.

20. Does an object need a net force to keep moving at constant velocity?

No.

21. What does constant velocity mean?

Constant speed and constant direction.

22. What is centripetal force?

The force required for circular motion, directed toward the center of the path.

23. Can several forces act on an object while its net force is zero?

Yes, if the forces balance.

24. What is mass?

A measure of the quantity of matter and an object’s resistance to acceleration.

25. What is inertia?

The property of matter that resists changes in motion.

26. How does mass affect acceleration for the same net force?

Greater mass produces less acceleration.

27. How does mass affect the force needed for a given acceleration?

Greater mass requires greater force.

28. Why is a car harder to accelerate than a shopping cart?

The car has more mass and inertia.

29. Are mass and weight the same?

No. Mass measures matter and inertia; weight is gravitational force.

30. Does mass change when an object moves to another location?

No.

31. Does weight change when an object moves to another location?

Yes, if the gravitational force changes.

32. How are mass and weight related?

Weight is proportional to mass in a given gravitational field.

33. What is Newton’s Second Law?

Net force equals mass times acceleration.

34. What is the formula for Newton’s Second Law?

(F_{\text{net}}=ma).

35. How do you calculate acceleration using net force and mass?

(a=F_{\text{net}}/m).

36. What happens to acceleration if force increases while mass stays constant?

Acceleration increases proportionally.

37. What happens to acceleration if mass increases while force stays constant?

Acceleration decreases.

38. In what direction does acceleration occur?

In the direction of the net force.

39. What is one newton equal to in base SI units?

(1\text{ N}=1\text{ kg}\cdot\text{m/s}^2).

40. What is the formula for an object’s weight?

(W=mg).

41. What does (g) represent?

Acceleration due to gravity.

42. How can a large force on a large mass produce the same acceleration as a small force on a small mass?

Both can have the same force-to-mass ratio.

43. What direction must a force act to slow an object down?

Opposite the object’s velocity.

44. What happens when a force acts perpendicular to an object’s velocity?

It causes centripetal acceleration and changes the direction of motion.

45. If two identical cars take the same curve, but one travels twice as fast, how do their centripetal forces compare?

The faster car requires four times the centripetal force.

46. What is equilibrium?

A state in which net force and acceleration are zero.

47. Can an object be in equilibrium while moving?

Yes, if it moves with constant velocity.

48. What happens when a constant net force acts in a fixed direction?

The object has constant acceleration.

49. What force acts on a freely falling body when air resistance is ignored?

Its weight, acting downward.

50. What happens when net force acts opposite an object’s velocity?

The object slows down.

51. What happens to a ball thrown straight upward?

It slows as it rises, momentarily stops, and then falls.

52. What is the acceleration of a ball thrown upward, ignoring air resistance?

Constant downward acceleration (g), even at its highest point.

53. What are the two components of projectile motion?

Horizontal motion and vertical motion.

54. How does gravity affect horizontal projectile motion?

It has no effect on horizontal motion when air resistance is ignored.

55. What happens to a projectile’s horizontal velocity?

It remains constant when air resistance is ignored.

56. What happens to a projectile’s vertical velocity?

It decreases while rising, reaches zero at the highest point, then increases downward.

57. What is simple harmonic motion?

Repeated oscillation caused by a restoring force proportional to displacement and directed oppositely.

58. What is Hooke’s Law?

(F=-kd).

59. What does (k) represent in Hooke’s Law?

The spring constant, which measures spring stiffness.

60. What does (d) represent in Hooke’s Law?

Displacement from the equilibrium position.

61. What does the negative sign in Hooke’s Law mean?

The restoring force acts opposite the displacement.

62. How does a larger spring constant affect restoring force?

It produces a greater restoring force for the same displacement.

63. How does greater displacement affect restoring force?

It increases the restoring force’s magnitude.

64. What is an elastic limit?

The limit beyond which a material becomes permanently deformed.

65. What is air resistance?

A force that acts opposite an object’s velocity relative to the air.

66. How does air resistance change as speed increases?

Air resistance generally increases.

67. How does air resistance approximately depend on speed for objects like baseballs and cars?

It is approximately proportional to speed squared.

68. What happens to a falling object’s net force as air resistance increases?

Its net downward force decreases.

69. What is terminal speed?

The constant falling speed reached when air resistance equals weight.

70. What is the net force at terminal speed?

Zero.

71. What happens to acceleration at terminal speed?

It becomes zero.

72. What motion results from zero net force?

Rest or constant velocity in a straight line.

73. What motion results from constant net force?

Constant acceleration.

74. What happens when force is parallel to velocity?

Speed increases in a straight line.

75. What happens when force is opposite velocity?

Speed decreases in a straight line.

76. What happens when force is perpendicular to velocity?

The object follows a circular path if the force remains perpendicular.

77. What motion results from a restoring force proportional to displacement?

Simple harmonic motion.

78. What happens when net force decreases as speed increases during a fall?

Acceleration decreases until velocity becomes constant.

79. What is Newton’s Third Law?

Every force exerted by one object produces an equal and opposite force on another.

80. What are action-reaction force pairs?

Equal and opposite forces that two interacting objects exert on each other.

81. If object A exerts a force on object B, what does object B do?

It exerts an equal force in the opposite direction on object A.

82. Do action-reaction forces act on the same object?

No, they act on different objects.

83. What is the law of universal gravitation?

Every object attracts every other object gravitationally.

84. How does gravitational force depend on the masses of two objects?

It is proportional to the product of their masses.

85. How does gravitational force depend on distance?

It is inversely proportional to the square of the distance between their centers.

86. What happens to gravitational force if either object's mass doubles?

The gravitational force doubles.

87. What happens to gravitational force if the distance between two objects doubles?

The force becomes one-fourth as large.

88. What is the gravitational constant represented by?

(G).

89. Why does Earth pull on you more strongly than the distant Sun does in the notes’ example?

You are much closer to Earth.

90. What determines your weight on Earth?

Your mass and your distance from Earth’s center.

91. What is a gravitational field?

The region around an object where its gravity can exert force.

92. Does a gravitational field exist if no other object is present?

Yes.

93. How does a gravitational field change with distance?

It becomes weaker farther from the object.

94. What can universal gravitation help explain?

Tides, comet motion, and orbital motion.

95. What shape are the orbits of the planets and Pluto according to the notes?

Ellipses.

96. What is the main cause of Earth's tides?

The Moon’s gravitational pull.

97. Why do the Moon’s gravitational forces produce tides?

Different parts of Earth’s oceans are different distances from the Moon.

98. What can you observe to help estimate tide levels, according to the notes?

The Moon’s position in the sky.

99. According to the notes, when is it low tide?

When the Moon is near the horizon.