1. Lesson 2
Newton’s First Law
Chapter Menu

2. Lesson 2 Reading Guide - KC
Newton’s First Law
What is Newton’s first law of motion?
How is motion related to balanced and unbalanced forces?
What effect does inertia have on the motion of an object?
Lesson 2 Reading Guide - KC

3. Vocabulary
Lesson 2-1

4. net force The combination of all forces acting on an object Vocabulary
Lesson 2-1

5. Vocabulary
balanced forces
Forces acting on an object that combine and form a net force of zero.
Lesson 2-1

6. Vocabulary
unbalanced forces
Forces acting on an object that combine and form a net force that is NOT zero.
Lesson 2-1

7. Newton’s first law of motion
Vocabulary
Newton’s first law of motion
An object will keep doing what it is doing until an unbalanced (outside) force acts upon that object
Lesson 2-1

8. inertia The tendency of an object to resist a change in its motion
Vocabulary
inertia
The tendency of an object to resist a change in its motion
Lesson 2-1

9. Identifying Forces
Lesson 2-1

14. The sum of all the forces acting on an object is the net force.
Identifying Forces
The sum of all the forces acting on an object is the net force.
The net force depends on the directions of the forces applied to an object.
Lesson 2-1

15. Identifying Forces (cont.)
When the forces applied to an object act in the same direction, the net force is the sum of the forces.
Lesson 2-1

16. How can you calculate the net force on an object if two forces are acting on it in the same direction?

18. Identifying Forces (cont.)
When forces act in opposite direction on an object, the net force is found by subtracting.
The net force is the sum of the positive and negative forces.
Lesson 2-1

20. Identifying Forces (cont.)
Balanced forces are forces that combine and form a net force of zero.
Forces that combine and form a net force that is not zero are unbalanced forces.
Lesson 2-1

21. Newton’s First Law Of Motion
Lesson 2-1

22. According to Newton’s first law of motion, if the net force on an object is zero, an object at rest will stay at rest, and a moving object will continue moving in a straight line with constant speed.
Lesson 2-2

25. Terminal Velocity: constant velocity reached when air resistance equals the force of gravity acting on a falling object

26. What happens to the velocity of a moving car if the forces on it are balanced?

27. Newton’s First Law of Motion (cont.)
Balanced forces acting on an object do not change the object’s speed and direction.
Newton’s first law of motion only applies to balanced forces acting on an object.
When unbalanced forces act on an object, the object’s velocity changes.
Lesson 2-2

28. Newton’s First Law of Motion (cont.)
How is motion related to balanced and unbalanced forces?
Lesson 2-2

29. Newton’s First Law of Motion (cont.)
The tendency of an object to resist a change in its motion is called inertia.
inertia
from Latin iners, means “without skill, inactive”
Lesson 2-2

31. Newton’s First Law of Motion (cont.)
What effect does inertial have on the motion of an object?
Lesson 2-2

32. Why do Objects Stop Moving?
Lesson 2-1

33. Why do objects stop moving?
For an object to start moving, a force greater than static friction must be applied to it.
Lesson 2-3

34. Why do objects stop moving?
To keep an object in motion, a force at least as strong as friction must be applied continuously.
Lesson 2-3

35. Objects stop moving because friction or another force acts on them.
Why do objects stop moving?
Objects stop moving because friction or another force acts on them.
Lesson 2-3

36. Unbalanced forces cause an object to move.
According to Newton’s first law of motion, if the net force on an object is zero, the object’s velocity does not change.
Inertia is a property that resists a change in the motion of an object.
Lesson 2 - VS

37. Which refers to forces that combine and form a net force that is not zero?
A. balanced forces
B. inertia
C. net force
D. unbalanced forces
Lesson 2 – LR1

38. Which could cause an object to stop moving?
A. friction
B. inertia
C. unbalanced forces
D. velocity
Lesson 2 – LR2

39. When equal forces act on an object in opposite directions, what is the net force on the object?
A. zero
B. one
C. equal
D. balanced
Lesson 2 – LR3

40. 3. Forces acting on an object cannot be added.
Do you agree or disagree?
3. Forces acting on an object cannot be added.
4. A moving object will stop if no forces act on it.
Lesson 2 - Now

41. Lesson 3 Reading Guide - KC
Newton’s Second Law
What is Newton’s second law of motion?
How does centripetal force affect circular motion?
Lesson 3 Reading Guide - KC

42. Lesson 3 Reading Guide - Vocab
Newton’s Second Law
Newton’s second law of motion
circular motion
centripetal force
Lesson 3 Reading Guide - Vocab

43. How do forces change motion?
Forces change an object’s motion by changing its speed, its direction, or both its speed and its direction.
Velocity is speed in a certain direction.
Only unbalanced forces change an object’s velocity.
Lesson 3-1

44. How do forces change motion? (cont.)
When unbalanced forces act on an object at rest, the object begins moving in the direction of the net force.
If the net force acting on a moving object is in the direction that the object is moving, the object will speed up.
If the direction of the net force on an object is opposite to the direction the object moves, the object slows down.
Lesson 3-1

45. When unbalanced forces act on a ball at rest, it moves in the direction of the net force.
Lesson 3-1

46. How do forces change motion? (cont.)
Unbalanced forces can change an object’s velocity by changing the object’s direction.
Another name for a change in velocity over time is acceleration.
Unbalanced forces make an object accelerate by changing its speed, its direction, or both.
Lesson 3-1

47. Newton’s Second Law of Motion
According to Newton’s second law of motion, the acceleration of an object is equal to the net force acting on the object divided by the object’s mass.
Lesson 3-2

48. Lesson 3-2

49. Newton’s Second Law of Motion (cont.)
The direction of acceleration is the same as the direction of the net force.
Acceleration is expressed in meters per second squared (m/s2), mass in kilograms (kg), and force in newtons (N).
Lesson 3-2

50. Circular Motion
Circular motion is any motion in which an object is moving along a curved path.
In circular motion, a force that acts perpendicular to the direction of motion, toward the center of the curve, is centripetal force.
Lesson 3-3

51. Circular Motion (cont.)
centripetal
from Latin centripetus, means “toward the center”
Lesson 3-3

52. Circular Motion (cont.)
Lesson 3-3

53. Circular Motion (cont.)
How does centripetal force affect circular motion?
Lesson 3-3

54. Circular Motion (cont.)
A satellite is an object that orbits a larger object.
A satellite tends to move along a straight path because of inertia.
Gravity is the centripetal force that keeps a satellite in orbit by changing its direction.
Lesson 3-3