10 - 3/10-4 : Newton’s Laws of Motion

1. 10-3/10-4: Newton’s Laws of Motion What are Newton’s three laws of motion?

2. Anticipatory Set

3. California Standards • Science Standard 8.2.e: Students know that when the forces on an object are unbalanced, the object will change its velocity. • Science Standard 8.2.f:Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion.

4. Input • inertia: the tendency of an object to resist a change in motion. • momentum: a characteristic of a moving object that depends on both the mass and the velocity of the object. • law of conservation of momentum: in the absence of outside forces, the total momentum of objects that interact does not change.

5. Input & Modeling Newton’s First Law of Motion • An object will remain at rest or moving at a constant velocity unless it is acted upon by an unbalanced force. • Inertia is the tendency of an object to resist change in motion. • Another name for Newton’s First Law of Motion is the LawofInertia. • The greater the object’s mass, the greater its inertia.

6. Input & Modeling Newton’s First Law of Motion

7. Input & Modeling Newton’s First Law of Motion

8. Input & Modeling Newton’s Second Law of Motion • Acceleration depends on the net force acting on the object and on the object’s mass. • Acceleration = Net Force ÷ Mass • Acceleration is measured in meters per second per second (m/s/s). • Net force is measured in Newtons (N), and mass is measured in kilograms (kg). • Net Force = Mass x Acceleration

9. Input & Modeling Newton’s Second Law of Motion

10. Input & Modeling A speedboat pulls a 55-kg water-skier. The skier accelerates at 2.0 m/s2. Calculate the net force that causes this acceleration. a = Fnet/m or Fnet = m x a Fnet = mxa F = 55 kg x 2.0 m/s2 F = 110 kg • m/s2 F = 110 N

11. C4U Practice Problem What is the net force on a 1,000-kg object accelerating at 3 m/s2? (1,000 kg x 3 m/s2) 3,000 N

12. C4U Practice Problem What net force is needed to accelerate a 25-kg cart at 14 m/s2? (25 kg x 14 m/s2) 350 N

13. Input & Modeling Newton’s Third Law of Motion • Newton’s third law of motion states that if one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. • Momentum = Mass x Velocity • The unit for momentum is measured in kilogram-meters per second (kgm/s)

14. Input & Modeling Newton’s Third Law of Motion

15. Input & Modeling Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 0.9 m/s? Momentum = Mass x Velocity Smaller sledgehammer = 3.0 km x1.5 m/s = 4.5 kgm/s Larger sledgehammer = 4.0 km x0.9 m/s = 3.6 kgm/s

16. C4U Practice Problem A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has greater momentum? Golf ball: 0.045 kg x 16 m/s = 0.72 kg•m/s Baseball: 0.14 kg x 7 m/s = 0.98 kg•m/s The baseball has greater momentum.

17. C4U Practice Problem What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s? momentum = 0.018 kg x 15 m/s momentum = 0.27 kg•m/s

18. Input & Modeling Law of Conservation of Momentum • The total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects. • Friction is an example of an outside force.

19. Input & Modeling Conservation of Momentum

20. Input & Modeling Conservation of Momentum In the absence of friction, momentum is conserved when two train cars collide.

21. HOMEWORK CONNECTION • Read pages 389-399 in your Science textbook. • Create a colored comic or poster that illustrates all three of Newton’s Laws of Motion. • Write a detailed SUMMARY of the section and complete the UNANSWERED QUESTIONS section of your notes. • Choose two of the remaining Depth & Complexity ICONS in your notes and explain how they relate to this section.