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April 15General Science Chapter 31 Acceleration and Momentum Chapter 3.

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Presentation on theme: "April 15General Science Chapter 31 Acceleration and Momentum Chapter 3."— Presentation transcript:

1 April 15General Science Chapter 31 Acceleration and Momentum Chapter 3

2 April 15General Science Chapter 32 Review Newton’s first law Weight of one kilogram on Earth’s surface Gravity

3 April 15General Science Chapter 33 Newton’s second law A net force acting on an object causes the object to accelerate in the direction of the force. The acceleration is affected by two things size of force mass of object

4 April 15General Science Chapter 34 Force If the force on an object increases, acceleration will increase for that object and if force decreases the acceleration will decrease. IF THE MASS REMAINS CONSTANT

5 April 15General Science Chapter 35 Mass A more massive object will take a larger force to give it the same acceleration as a smaller massed object.

6 April 15General Science Chapter 36 Equation for Newton’s 2 nd law We can also use the “magic” triangle

7 April 15General Science Chapter 37 Units on force Last chapter we learned that force has units of Newtons. From Newton’s second law equation,

8 April 15General Science Chapter 38 Example How much force is needed to accelerate a 70-kg rider and the 200-kg motorcycle the rider is on at 4 m/s 2 ? F = 270 kg x 4 m/s N

9 April 15General Science Chapter 39 You try How much force is needed to accelerate a 60-kg person and the 500-kg car the person is in at 6 m/s 2 ? F = 560 kg x 6 m/s N

10 April 15General Science Chapter 310 You try A 63-kg skater pushes off from a wall with a force of 300 N. What is the skater’s acceleration? 300 N = 63 kg a a = 300 N ÷ 63 kg 4.76 m/s 2

11 April 15General Science Chapter 311 Review #1 What is Newton’s 2nd Law of Motion? What equation do we use with the 2nd Law of Motion? What 2 things will affect acceleration? What are the units for Force? True or False: A more massive object will take less force to accelerate?

12 April 15General Science Chapter 312 Acceleration due to gravity Near Earth’s surface, gravity causes all falling objects to accelerate at a rate of 9.8 m/s 2, regardless of their mass. Acceleration due to gravity is represented by the letter g. Does this number seem familiar?

13 April 15General Science Chapter 313 Weight The weight of an object is the force of gravity acting on it.

14 April 15General Science Chapter 314 Reality check Do all objects really fall with the same acceleration?

15 April 15General Science Chapter 315 Air resistance The force air exerts on a moving object. Acts in the opposite directions to which an object is moving. For falling objects, air resistance pushes up while gravity pulls down.

16 April 15General Science Chapter 316 Air resistance Depends on the speed, size, and shape of the object. The larger the object, the more air resistance affects it. The faster an object is moving, the more air resistance affects it.

17 April 15General Science Chapter 317 Terminal velocity As an object falls, air resistance gradually increases until it equals the pull of gravity. At this point, the object stops accelerating and moves with a constant velocity – called its terminal velocity.

18 April 15General Science Chapter 318 Example A ball is dropped from the roof of a 50-m tall building. It hits the ground 3.2 s later. What is its velocity right before it hits the ground? a = v ÷ t OR v = a t v = 9.8 m/s 2 x 3.2 s m/s

19 April 15General Science Chapter 319 Review #2 Define air resistance. What is air resistance dependent upon? What is terminal velocity? What is the acceleration of gravity near the surface of the earth? How do we determine the weight of an object?

20 April 15General Science Chapter 320 Projectiles Anything that’s shot or thrown through the air. Will always follow a curved path.

21 April 15General Science Chapter 321 Projectile motion Can be split into independent vertical and horizontal motions.

22 April 15General Science Chapter 322 The horizontal part Once the object is released, there is no force acting on it horizontally. If there is no force, it must maintain a constant horizontal velocity.

23 April 15General Science Chapter 323 The vertical part There is a force acting – gravity The object is pulled downward with a constant acceleration of 9.8 m/s 2.

24 April 15General Science Chapter 324 Circular motion Objects moving in circles are constantly accelerating. This acceleration is towards the center of the circle or curve. It is called centripetal acceleration. Towards the center of a circle or a curved path.

25 April 15General Science Chapter 325 Centripetal force The force that causes an object to move in a curved or circular path.

26 April 15General Science Chapter 326 Weightlessness To be truly weightless, an object would have to be free from gravity. To feel weightless, something has to be in free fall along with its surroundings.

27 April 15General Science Chapter 327 Weightlessness How does a scale measure weight? If it can’t push back, it would read zero. You would feel weightless.

28 April 15General Science Chapter 328 Review #3 What is a projectile? What are the 2 components of a projectile? What does centripetal mean? Why are objects weightless during free fall?

29 April 15General Science Chapter 329 Newton’s 3 rd law To every action, there is an equal and opposite reaction. When one object exerts a force on a second object, the second object exerts a force on the first object that is equal in size and opposite in direction.

30 April 15General Science Chapter 330 Examples Released balloon Firing a gun Jumping out of a boat rockets

31 April 15General Science Chapter 331 Balanced forces? Action-reaction pairs of forces are not balanced forces. The forces act on different objects. To be balanced forces, the equal and opposite forces must act on the same object

32 April 15General Science Chapter 332 Momentum A property a moving object has because of its mass and velocity

33 April 15General Science Chapter 333 Momentum Has units of kg∙m/s Has direction, because velocity has direction

34 April 15General Science Chapter 334 Momentum Which has a higher momentum, a 50-kg dolphin swimming at 16.4 m/s or a 6300-kg elephant walking at 0.11 m/s? Dolphin – (50 kg)(16.4 m/s) = 820 kg∙m/s Elephant – (6300 kg)(0.11 m/s) = 693 kg∙m/s The dolphin has higher momentum.

35 April 15General Science Chapter 335 Example Which has higher momentum, a 65-kg person running at 9 m/s or a 60-kg person running at 11 m/s? 1 st person – (65 kg)(9 m/s) = 585 kg∙m/s 2 nd person – (60 kg)(11 m/s) = 660 kg∙m/s The 60-kg person has higher momentum.

36 April 15General Science Chapter 336 Law of conservation of momentum The total amount of momentum of a group of objects does not change unless outside forces act on the objects.

37 April 15General Science Chapter 337 Momentum transfer Momentum can be transferred from one object to another. Think about playing pool The cue ball transfers its momentum to the ball it hits. The momentum lost by the cue ball is gained by the other ball.

38 April 15General Science Chapter 338 Example A 5-kg object with a velocity of 6 m/s strikes a motionless 10-kg ball. The 5 kg object stops moving. What is the velocity of the 10 kg ball after the collision? Momentum of object before collision: (5 kg)(6 m/s) = 30 kg∙m/s

39 April 15General Science Chapter 339 Example continued When the object stops, it loses all its momentum. The momentum it lost is transferred to the ball. Momentum of the ball after collision: (10 kg)(velocity) = 30 kg∙m/s Velocity = 3 m/s

40 April 15General Science Chapter 340 Example continued Notice that the velocity was not conserved, but momentum was.

41 April 15General Science Chapter 341 Review #4 What is Newton’s 3rd Law of Motion? Define momentum. What units does momentum have? What is the law of conservation of momentum?

42 April 15General Science Chapter 342 Chapter 3 Review State all 3 Laws of Motion What 2 things affect acceleration on an object What is air resistance dependent upon? How are the Law of Inertia and the Law of conservation of momentum related?


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