1. IPC – Unit 2 Newton’s Laws

2. Newton’s Laws of Motion Forces change the motion of an object in very specific ways Sir Isaac Newton (1642-1727) was able to state the Laws that describe the effects of forces.

3. Newton’s 1st Law of Motion: An object at rest tends to stay at rest, and an object in motion tends to stay in motion, unless acted upon by an outside force. Also called the Law of Inertia Inertia: the tendency for an object to resist its change in motion. *** The greater the mass of the object – the greater it’s inertia. ***

4. Newton’s 2nd Law of Motion: A force acting on an object tends to accelerate that object in the direction of the force. Also called the Law of Acceleration The greater the mass the greater the resistance to the acceleration. ******

5. Newton’s 2nd Law of Motion can be expressed in an equation: Force = (Mass) x (Acceleration) F = ma Units: F = kg·(m/s2) m = kg a = m/s2

6. Example: What is the force exerted on a 1000 kg car going 15 m/s2?

7. Problem #1: A weightlifter raises a 150kg barbell with an acceleration of 4m/s2. How much force does the weightlifter use to raise the barbell?

8. Problem #2: An ice skater lifts his partner above his head with an acceleration of 3.5m/s2. The skater exerts a force of 225N. What is the mass of his partner?

9. Problem #3: The motion of a 12kg object is opposed by a 30N force of friction. At what rate does friction slow the object down?

10. Free Fall: The acceleration of any object under the sole influence of gravity. Characteristics of free fall objects: Do not incounter air resistanceDo not incounter air resistance On Earth the acceleration of gravity is a constant 9.8 m/s2On Earth the acceleration of gravity is a constant 9.8 m/s2 *** Formula for acceleration: a = (v f – v i )/t ***

11. Example: What is the velocity of a rubber ball dropped from a building roof after 5 seconds?

12. Problem #4: A car entering a freeway ramp accelerates at 9 km/hr/sec from 14km/hr to 50 km/hr. What is the car’s time?

13. Problem #5: A car’s velocity changes from 80 km/hr to 40 km/hr as it travels up a hill in 10 seconds. What is the car’s acceleration?

14. Newton’s Third Law of Motion: For every action there is an equal and opposite reaction. *** Action/Reaction always happens in pairs!!! ***

15. Momentum: Is the product of an objects mass and velocity.

16. Momentum can be expressed with the following equation: Momentum = (mass) x (velocity) P = m·v Units: Momentum = kg·(m/s) Mass = kg Velocity = m/s An increase (or decrease) in either mass or velocity will increase (or decrease) momentum ******

17. Example: Find the momentum of an 7.2kg rock that is rolling down a hill with a velocity of 3.0m/sec.

18. Problem #6: A 166.25 kilogram motorcycle is moving at a speed of 78.75 m/s. What is the momentum of the cycle?

19. Problem #7: A child with a momentum of 200 kg-m/sec has a mass of 20 kg. With what velocity is the child moving?

20. Law of Conservation of Momentum: In the absence of any external forces, the total momentum of the system never changes. Characteristics of these types of problems: No frictionNo friction No air resistanceNo air resistance The sum of all initial momentums equals the sum of all final momentumsThe sum of all initial momentums equals the sum of all final momentums

21. Law of Conservation of Momentum as an equation: P 1 = P 2 m 1 v 1 = m 2 v 2 P 1 = Momentum of 1st object m 1 = Mass of 1st object v 1 = Velocity of 1st object P 2 = Momentum of 2nd object m 2 = Mass of 2nd object v 2 = Velocity of 2nd object

22. Example: The queue ball on a pool table has a mass of 150 grams and a velocity of 10 m/s, it then strikes the 8-ball which is at rest and transfers all of it’s momentum to the 8- ball. If the 8-ball has a mass of 200 grams, then what is its velocity? What is the momentum of the 8-ball?

23. Problem #8: A steel ball with a mass of 150 kg is rolling at a rate of 5m/s. It hits a brass ball which then has a velocity of 3.5m/s. What is the mass of the brass ball?

24. Problem #9: A 1.5 kg pinball with a velocity of 5 m/s collides with a second pinball with a mass of 2.5 kg. What is the final velocity of the second pinball after the collision?