Chapter 12 - Forces

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

2. TN Standards • CLE.3202.3.2: Investigate and apply Newton’s three laws of motion • CLE.3202.4.1: Explore the difference between mass and weight • CLE.3202.4.2: Relate gravitational force to mass • CLE.3202.3.3: 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 – 10/14/15 • How many laws of motion did Newton create? • 3

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 non-zero ( or unbalanced ) net force • Objects change their state of motion only when a non-zero 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 ) • More inertia an object has, the harder it is to change its state of motion • 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 F/m = a • 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 mass, a larger force accelerates more • 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. Bellwork – 10/19/15 • What does gravity depend on ( what are the key factors of gravity )?

14. 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?

15. 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 [ g on Earth = 9.81 m/s2 ]

16. Law of Universal Gravitation

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

18. 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 )

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

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

21. Projectile Motion • Orbiting is projectile motion

22. 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?

23. Bellwork • What is the difference between weight and mass?

24. 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?

25. Action and Reaction Forces • Foot on Ball – ACTION • Ball on Foot – REACTION

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

27. 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

28. 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

29. 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?

30. 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?

31. 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

33. 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?

34. Bellwork • What is Newton’s 3rd Law ( in your own words )?