Table of Contents

1. Forces Chapter 11 Table of Contents Section 1 Laws of Motion Section 2 Gravity Section 3 Newton’s Third Law

2. Section 1 Laws of Motion Chapter 11 Objectives • Identifythe law that says that objects change their motion only when a net force is applied. • Relatethe first law of motion to important applications, such as seat belt safety issues. • Calculateforce, mass, and acceleration by using Newton’s second law.

3. Section 1 Laws of Motion Chapter 11 Bellringer In some cases, an applied force is balanced by an opposite force, and there is no change in motion. In other cases, an applied force is not balanced by an opposite force, and the result is acceleration in the direction of the applied force. Look at the following illustrations, and identify the forces and motion in each one. (Illustrations are shown on the next slide.)

4. Section 1 Laws of Motion Chapter 11 Bellringer • 1. In one drawing, no motion is likely to occur. • Which drawing is it? • 2. In which diagram are the forces clearly balanced? • How does this relate to your answer to item 1? • If more force is exerted by the person, does the opposite force increase to match the new force, stay the same or decrease?

5. Newton's Laws of Motion

6. Section 1 Laws of Motion Chapter 11 Newton’s First Law • Newton’s first law of motionstates thatan object at rest remains at rest and an object in motion stays in motion unless it experiences an unbalanced force. • Objects tend to maintain their state of motion. • Skateboard demo

8. Inertiais the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction until an unbalanced force acts on the object. • Basically inertia is the name given to describe Newton’s 1st law.

9. Section 1 Laws of Motion Chapter 11 Newton’s First Law • Inertia is related to an object’s mass. • Mass is a measure of inertia. • The bigger the mass the bigger the objects inertia.

11. Seat belts and car seats provide protection. • Because of inertia, you slide toward the side of a car when the driver makes a sharp turn. • When the car you are riding in comes to a stop, your seat belt and the friction between you and the seat stop your forward motion.

12. Video – Newtons 1st Law 6min

14. Section 1 Laws of Motion Chapter 11 Newton’s Second Law • Newton’s second law of motionstates that the unbalanced force acting on an object equals the object’s mass times its acceleration. • Force equals mass times acceleration. Force = mass  acceleration F = ma • Force is measured in newtons (N). 1 N = 1 kg  1 m/s2 Video – Newtons 2nd Law 1min

15. F a m Newton’s Second Law F m F = ma F: force (N) m: mass (kg) a: accel (m/s2) 1 N = 1 kg ·m/s2

16. Section 1 Laws of Motion Chapter 11 Newton’s Second Law

17. Section 1 Laws of Motion Chapter 11 Math Skills Newton’s Second Law Zookeepers lift a stretcher that holds a sedated lion. The total mass of the lion and stretcher is 175 kg, and the lion’s upward acceleration is 0.657 m/s2. What is the unbalanced force necessary to produce this acceleration of the lion and the stretcher? 1. List the given and unknown values. Given: mass, m = 175 kg acceleration, a = 0.657 m/s2 Unknown: force, F = ? N

18. Section 1 Laws of Motion Chapter 11 Math Skills 2. Write the equation for Newton’s second law. force = mass  acceleration F = ma 3. Insert the known values into the equation, and solve. F = 175 kg  0.657 m/s2 F = 115 kg m/s2 = 115 N

19. Section 1 Laws of Motion Chapter 11 Newton’s Second Law • Newton’s second law can also be stated as follows: The acceleration of an object is proportional to the net force on the object and inversely proportional to the object’s mass.

20. Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's Second Law, you can compute how much force Mike is applying to the car. • Answer = _____________ • 50 newtons

21. How much force would the lady have to apply to the van? • Video- Newtons 2nd law 2min

22. Consider the motion of a Hot Wheels car down an incline • This animation depicts some additional information about the car's motion. The velocity and acceleration of the car are depicted by vector arrows. The direction of these arrows are representative of the direction of the velocity and acceleration vectors. Note that the velocity vector is always directed in the same direction which the car is moving

23. Section 2 Gravity Chapter 11 Objectives • Explainthat gravitational force becomes stronger as the masses increase and rapidly becomes weaker as the distance between the masses increases. • Evaluatethe concept that free-fall acceleration near Earth’s surface is independent of the mass of the falling object. • Demonstratemathematically how free-fall acceleration relates to weight. • Describeorbital motion as a combination of two motions.

24. Section 2 Gravity Chapter 11 Law of Universal Gravitation • Sir Isaac Newton (1642–1727) generalized his observations on gravity in a law now known as thelaw of universal gravitation. • Universal Gravitation Equation • m1 and m2 are the masses of the two objects • d is the distance between the two objects • G is a constant for gravity (6.67 X 10-11 N m2/kg2) Video- universal gravitation Bill Nye- 2min Video – universal gravitation- 2min

25. Got Gravity???

26. Section 2 Gravity Chapter 11 Law of Universal Gravitation • All matter is affected by gravity. • Two objects, whether large or small, always have a gravitational force between them. • When something is very large, like Earth, the force is large. • Gravitational force increases as mass increases. More Mass= More Gravity • Video – gravitation 2min • Gravitational force decreases as distance increases. More distance = less gravity

27. Kite flying link- 3.5 min

28. Section 2 Gravity Chapter 11 Law of Universal Gravitation

29. Greater distance from Earth= Less Gravity

32. Section 2 Gravity Chapter 11 Free Fall and Weight • Free fallis the motion of a body when only the force of gravity is acting on the body. • Free-fall acceleration near Earth’s surface is constant. • If we disregard air resistance, all objects near Earth accelerate at 9.8 m/s2. • Freefall acceleration is often abbreviated as the letter g, so g = 9.8 m/s2.

33. Elephant and feather fallingWith air resistance and without

34. Section 2 Gravity Chapter 11 Free Fall and Weight • Weight is equal to mass times free-fall acceleration. weight = mass x gravity w = mg

36. Weight is different from mass. • Mass is a measure of the amount of matter in an object. Mass of an object is always the same anywhere in the universe. • Weight is the pull of gravity on an objects mass. • Gravity can change so weight can change.

37. Weight of 150 lb person on Earth(At sea level) • Mercury- 55 lbs • Venus- 130 lbs • Jupiter- 380 lbs • Top of Mt. Everest • = 148 pounds

38. Section 2 Gravity Chapter 11 Bellringer Recall that weight is defined as a measure of the gravitational force exerted on an object. Use knowledge you have about gravity to answer the questions in the following situations: 1. Elvis is a student whose mass is 70 kg. On Earth’s surface, Elvis weighs about 690 N. Suppose Elvis could stand on the surface of the following bodies in the solar system. In the blanks provided, match Elvis’ weight with the letter of the appropriate body. (Note that Earth has a mass of 6.0 x 1024 kg.) PlanetElvis’ weight a. Jupiter (m = 1.9 x 1027 kg) 780 N _______ b. Venus (m = 4.9 x 1024 kg) 113 N _______ c. Neptune (m = 1.0 x 1026 kg) 260 N _______ d. Mercury (m = 3.3 x 1023 kg) 1800 N _______ e. Earth’s moon (m = 7.4 x 1022 kg) 620 N _______

39. Section 2 Gravity Chapter 11 Bellringer, continued 2. Suppose Elvis is in orbit around Venus at a distance twice as far from the planet’s center as the surface of Venus is. Would you expect his weight to be greater than, less than, or equal to his weight on the surface of the planet?

41. Section 2 Gravity Chapter 11 Free Fall and Weight • Velocity is constant when air resistance balances weight. • The constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity is called theterminal velocity. • Video- falling objects 6min

42. Chapter 11 Section 2 Gravity Terminal Velocity

43. Question • When a skydiver jumps from a helicopter, his terminal velocity before opening the parachute reaches approximately 320 km/h. • Why does the rate of descent of the skydiver slow when the parachute opens? After all, the skydiver still has the same mass.

44. Answer • When the skydiver’s parachute is unopened, his surface area is much less than when the parachute is open. Therefore, the air resistance is much less and the skydiver will fall at a faster rate. Once the parachute opens, the surface area of the parachute creates far more resistance with the air and the skydiver’s descent is slowed. The force of gravity is exactly the same, and the mass has not changed, but the air resistance is greater.

47. Section 2 Gravity Chapter 11 Free Fall and Motion • Orbiting objects are in free fall. • The moon stays in orbit around Earth because Earth’s gravitational force provides a pull on the moon. • Two motions combine to cause orbiting. • Orbiting =Forward motion + gravity.

48. Section 2 Gravity Chapter 11 Two Motions Cause Orbiting

49. Section 2 Gravity Chapter 11 Projectile Motion and Gravity • Projectile motionis the curved path an object follows when thrown, launched, or otherwise projected near the surface of Earth.