1. 12.2 Newton’s First and Second Laws of Motion
Key Concepts:
1. How does Newton’s first law relate change in motion to a zero net force?
How does Newton’s second law relate force, mass, and acceleration?
3. How are weight and mass related?

2. 12.2 Newton’s First and Second Laws of Motion
Aristotle, Galileo, and Newton
Aristotle
Ancient Greek scientist and philosopher
Used observations and logical reasoning to make scientific discoveries
Believed that a force is required to keep an object moving at a constant speed.
Galileo
Italian scientist
Used ramps and balls to experiment with gravity
Concluded that moving objects not subjected to friction or any other forces would continue to move indefinitely.
Newton
English physicist and mathematician
Used the work of previous scientists to work on his own experiments
Defined mass and force and then introduced the laws of motion.

3. 12.2 Newton’s First and Second Laws of Motion
Newton’s First Law
A. The state of motion of an object does not change
as long as the net force acting on the object is
zero.
B. Unless an unbalanced force acts, an object at rest
remains at rest, and an object in motion remains
in motion with the same speed and direction.

4. 12.2 Newton’s First and Second Laws of Motion
C. Also called the Law of Inertia 1. Inertia- tendency of an object to resist a change in motion. 2. Examples: Wearing your seatbelt in a moving car.

5. 12.2 Newton’s First and Second Laws of Motion

6. 12.2 Newton’s First and Second Laws of Motion

7. 12.2 Newton’s First and Second Laws of Motion

8. 12.2 Newton’s First and Second Laws of Motion

9. 12.2 Newton’s First and Second Laws of Motion
D. From Figures 12A –D pages :
What is the effect of inertia on the car?
What effect does inertia have on the dummy?
How is the mass of a passenger related to the passenger’s inertia?

10. 12.2 Newton’s First and Second Laws of Motion
4. All objects have inertia.
Large objects require more force to change its
motion, so mass is a measure of inertia.

11. 12.2 Newton’s First and Second Laws of Motion
Newton’s Second Law of Motion
A. Unbalanced force causes
an object’s velocity to
change or to accelerate.
B. Apply a force to throw a ball, it accelerates. Apply more force, the ball will accelerate more.

12. 12.2 Newton’s First and Second Laws of Motion
The acceleration of an object is equal to the net force acting on it divided by the object’s mass.
The acceleration of an object is always in the same direction as the net force.
When a net force acts in the direction opposite to the object‘s motion, force produces deceleration.

13. 12.2 Newton’s First and Second Laws of Motion

14. 12.2 Newton’s First and Second Laws of Motion
Practice Problems
1. Zoo keeps lift a stretcher that holds a sedated lion. The total mass of the lion and stretcher is 175 kg, and the upward acceleration of the lion and the stretcher is m/s2. What force is needed to produce this acceleration of the lion and the stretcher?

15. 12.2 Newton’s First and Second Laws of Motion
1. Work: m = a= F = Answer:

16. 12.2 Newton’s First and Second Laws of Motion
What net force is needed to accelerate a
1.6 x 103 kg automobile forward at 2.0 m/s2?
Work:
m = a=
F =
Answer:

17. 12.2 Newton’s First and Second Laws of Motion
3. A baseball accelerates downward at 9.8 m/s2. If the gravitational force is the only force acting on a the baseball and is 1.4 N, what is the baseball’s mass? Work: m = a= F = Answer:

18. 12.2 Newton’s First and Second Laws of Motion
A sailboat and its crew have a combined mass of kg. If a net force of 895 N is pushing the sailboat forward, what is the sailboat’s acceleration?
Work:
m = a=
F =
Answer:

19. 12.2 Newton’s First and Second Laws of Motion
The net forward force on the propeller of a 3.2 kg model airplane is 70 N. What is the acceleration of the airplane?
Work:
m = a=
F =
Answer:

20. 12.2 Newton’s First and Second Laws of Motion
Weight and Mass
A. Weight – force of gravity acting on an object.
B. Equal to the mass of an object times the acceleration due to gravity acting on it.

21. 12.2 Newton’s First and Second Laws of Motion
C. Weight = Mass x Acceleration due to gravity 1. W = m x g 2. Weight- measured in newtons (N) Mass- measured in kilograms (kg) Acceleration due to gravity = 9.8 m/s2

22. 12.2 Newton’s First and Second Laws of Motion
Assignment: