1. - Newton’s First and Second Laws - Gravity 3 - Newton’s Third Law
Chapter 12 - Forces
- Newton’s First and Second Laws
- Gravity
3 - Newton’s Third Law

2. TN Standards
CLE : Investigate and apply Newton’s three laws of motion
CLE : Explore the difference between mass and weight
CLE : Relate gravitational force to mass
CLE : Examine the Law of Conservation of Momentum in real-world situations
CLE.3202.Math.1: Understand the mathematical principles behind the science of Physics

3. Bellwork
How many laws of motion did Newton create?

4. 1 – Newton’s 1st and 2nd Laws
Key Questions:
What makes an object speed up, slow down, or change directions?
What determines how much an object speeds up or slows down?

5. Newton’s First Law
An object at rest remains at rest and an object in motion maintains its velocity unless it experiences a net force
Objects change their state of motion only when a net force is applied
Objects tend to maintain their state of motion

6. Inertia “Laziness” of all matter based on mass
Is the tendency of an object to stay at rest or to move at constant velocity ( if moving )
Seat belts and car seats

7. QuickLab – Newton’s 1st Law
Place an Index Card over a glass; Coin on card
Flick the card sideways off the glass – what happens to the coin?
Does coin move with Index Card?
Repeat but slowly pull card sideways – what happens to the coin?
Explain the results using Newton’s 1st Law
In your notebook ( lab grade )

8. Newton’s Second Law
The unbalanced force acting on an object equals the object’s mass times its acceleration
Net force equals mass times acceleration
F = ma
Unbalanced force on an object determines how much an object speeds up or slows down

9. Newton’s Second Law
Force is measured in Newtons ( 1 N = 1 kg x 1 m/s2 )
For equal forces, a larger mass accelerates less
Acceleration depends on force and mass

10. Newton’s Second Law
Force is measured in Newtons ( 1 N = 1 kg x 1 m/s2 )
For equal forces, a larger mass accelerates less
Acceleration depends on force and mass

11. 1 – Newton’s 1st and 2nd Laws
Key Questions:
What makes an object speed up, slow down, or change directions?
What determines how much an object speeds up or slows down?

12. Bellwork What is Newton’s First Law (in your own words)
What is Newton’s Second Law (in your own words)

13. 2 – Gravity Key Questions: How are weight and mass related?
Why do objects fall to the ground when dropped?
What is the relationship between free-fall acceleration and mass?
Why does a projectile follow a curved path?

14. Weight and Mass Force on an object due to gravity is WEIGHT
Weight is measured in Newtons
Free-fall acceleration is a constant acceleration all objects on earth experience
Weight is equal to mass times free-fall acceleration
w = mg

15. Law of Universal Gravitation
All objects in universe attract each other through the force of gravity
𝑭=𝑮 𝒎 𝟏 𝒎 𝟏 𝒅 𝟐

16. Law of Universal Gravitation
All matter is affected by gravity
Gravitational force increases with mass OR decreases with distance

17. Free Fall
Without air resistance, all objects falling near Earth’s surface accelerate at the same rate regardless of their mass
Due to the Law of Gravitation
Air resistance can balance weight
EXAMPLE : Leaf falling at constant velocity
TERMINAL VELOCITY ( max velocity obtained )

18. Projectile Motion
Curved path of an object thrown, launched, kicked, or otherwise projected near Earth’s surface

19. Projectile Motion Two components – horizontal and vertical
Curved path when both are combined

20. Projectile Motion
Orbiting is projectile motion

21. 2 – Gravity Key Questions: How are weight and mass related?
Why do objects fall to the ground when dropped?
What is the relationship between free-fall acceleration and mass?
Why does a projectile follow a curved path?

22. Bellwork
What is the difference between weight and mass?

23. 3 – Newton’s Third Law Key Questions:
What happens when an object exerts a force on another object?
How do you calculate the momentum of an object?
What is the total momentum after objects collide?

24. Action and Reaction Forces
Foot on Ball – ACTION
Ball on Foot – REACTION

25. Newton’s Third Law
For every ACTION force there is an opposite and equal REACTION force

26. Newton’s Third Law Forces always occur in pairs
Forces in a force pair do not act on the same object
Do not cancel each other
Equal forces do not always have equal effects

27. QuickLab – Action/Reaction Forces
Hang a 2 kg mass from a spring scale
Observe and record the reading on the spring scale
With the mass on the first scale, link a second scale to the first
Observe/record readings from both scales

28. QuickLab – Action/Reaction Forces
QUESTIONS:
What are the action and reaction forces in the spring scale-mass system that you have constructed?
How did the readings on both scales compare in the last step? Explain how this demonstrates Newton’s 3rd Law?

29. Momentum A property of all moving objects
Along a straight line, momentum is the product of an object’s mass and velocity
p = mv
Increases as mass and velocity increases
Force is related to change in momentum
How does moving the catcher’s glove back change the force needed to stop the ball?

30. Conservation of Momentum
The total amount of momentum in an isolated system is conserved
Total momentum of two or more objects after a collision is the same as the momentum before
Explained by 3rd Law

32. 3 – Newton’s Third Law Key Questions:
What happens when an object exerts a force on another object?
How do you calculate the momentum of an object?
What is the total momentum after objects collide?