1. What is inertia? An object’s resistance to changing its motion.
white board marker
hoop
For this class demo, balance a hoop on the top of a weighted bottle, and the marker on the hoop, as shown in the drawing.
Ask students: What do you think will happen when I knock the hoop from the bottle?
After student discussion and predictions, quickly knock the hoop from its location between the bottle and the marker. If done correctly, the marker falls straight into the bottle.
This demonstrates inertia; the marker resists changing direction when the hoop is knocked away.
Alternatively, show an online video of the same demo, such as:
Home Experiment: Newton's First Law/Law of Inertia (55-second video; good for practicing) at
Conceptual Physics - Inertia Hoop Demo (2:47-minute video; good for students) at
bottle

5. The amount of inertia possessed by an object is dependent solely upon its mass.

6. Mass—A Measure of Inertia
2.2 pounds near Earth’s surface.

7. Here is my first law. I called it NEWTON’S FIRST LAW

8. Deciphering Newton’s First Law
“Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.”
—Sir Isaac Newton
Principia Mathematica (1687)
Write: In your own words, what does this mean?
Make sure students do not confuse “every body” with “everybody.” Clarify that Newton wrote “every body,” meaning “every object.”
This slide brings in the Common Core.
Image sources:
The cover page of Newton’s book, Naturalis Principia Mathematica: 1687 Wikimedia Commons
A portrait of Isaac Newton: 1689 Sir Godfrey Kneller, Wikimedia Commons
Unless an unbalanced force acts on an object,
An object at rest stays at rest
An object in motion stays in motion
Isaac Newton,

9. Newton’s 1st Law and You
Wear seat belts!

10. NEWTON’S FIRST LAW is also known as THE LAW OF INERTIA

11. Here is my second law. I called it NEWTON’S SECOND LAW

12. Newton’s Second Law of Motion

13. Newton’s Second Law Part 1:
The net force on an object causes its acceleration.

14. Net Force ΣF = F1 +F2 + F3 + … Fnet = F1 + F2 + F3 + …
Net Force, Total Force, Resultant Force
ΣF = F1 +F2 + F3 + …
Fnet = F1 + F2 + F3 + …

16. Mechanical Equilibrium
The resultant force is zero
All forces cancel out
There is no change in the objects motion

17. When net force is zero…

18. Car at Constant Speed ΣF = Fa = 50 N Friction = 50 N
Normal Force = 2000 N
ΣF =
Fa = 50 N
Friction = 50 N
Weight = 2000 N

19. Net Force Causes Acceleration acceleration ~ net force
To increase the acceleration of an object, you must increase the net force acting on it.
An object’s acceleration is directly proportional to the net force acting on it:
acceleration ~ net force
(The symbol ~ stands for “proportional to.”)

20. Newton’s Second Law Part 2:
The mass of an object resists acceleration.

21. Force Directly proportional means…
Acceleration
Directly proportional means…
if you increase the force applied to the object the acceleration also increases.

22. Acceleration
Inversely means…
if you increase the mass of the object the acceleration does the opposite it decreases.
Mass

23. Mass Resists Acceleration
The same force applied to twice as much mass results in only half the acceleration.
The acceleration is inversely proportional to the mass.

24. Newton’s Second Law-
Net Force causes acceleration, mass resists it.
a = Fnet or Fnet = ma m

25. 2nd Law
When mass is in kilograms and acceleration is in m/s/s, the unit of force is in Newtons (N).
One newton is equal to the force required to accelerate one kilogram of mass at one meter/second/second.

26. Force is measured in Newtons;
(1.00kg)(1.00m/s2)= 1 N (Newton)

27. Check Your Understanding
1. What acceleration will result when a 12 N net force applied to a 3 kg object? A 6 kg object?
2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass.
3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?
4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?

28. Check Your Understanding
1. What acceleration will result when a 12 N net force applied to a 3 kg object?
12 N = 3 kg x 4 m/s/s
2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass.
16 N = 3.2 kg x 5 m/s/s
3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?
66 kg-m/sec/sec or 66 N
4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?
9800 kg-m/sec/sec or 9800 N

29. do the math!
A car has a mass of 1000 kg. What is the acceleration produced by a force of 2000 N?
If the force is 4000 N, what is the acceleration?

30. do the math!
How much force, or thrust, must a 30,000-kg jet plane develop to achieve an acceleration of 1.5 m/s2?

31. 10 N
20 N
20 kg
a = 0.50 m/s2 right

32. Free Fall Explained
How come all objects free fall with the same acceleration?

33. Free Fall Explained
As the gravitational force (weight) on an object increases, so does its mass.
Net Force causes
acceleration and
mass resists

34. System Diagrams vs. FBD

35. Check Your Understanding
You toss a ball vertically upward. Draw an FBD of the ball just before it leaves your hand.