Newton’s Laws of Motion

1. 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.

2. No mom, I don’t want to go! Newton’s 1st Law of Motion Law of Inertia INERTIA is… the tendency for an object to resist its change in motion. It wants to stay where it is. First Law basically states that… An object in motion tends to stay in motion, while an object at rest tends to stay at rest until a force acts upon the object.

3. Newton’s 1st Law of Motion - Continued The greater the mass of the object – the greater it’s inertia. Think about it like this… The book is sitting on the table is at rest. The book will stay there (remain at rest) until someone moves it (the outside force).

4. Newton’s 1st Law of Motion - Continued Another example: If you were standing the same distance from a softball being hit or a baseball being hit which one would hurt more if it hit you? Which has more inertia?

5. Newton’s 2nd Law of Motion Law of Acceleration Second Law basically states that…a force acting on an object causes the object to accelerate in the direction of that force. Force causes acceleration. Greater the mass – the greater the resistance to acceleration.

6. Newton’s 2nd Law of Motion - Continued Let’s think about this one…if the soccer player kicks the soccer ball – which direction will the soccer ball go? Force causes acceleration of the object to accelerate in the direction of that force (the kicking of the ball).

7. Newton’s 2nd Law of Motion - Continued Think about it like this… If the blue truck has a mass of 25,000kg and the red truck has a mass of 30,000kg which truck is going to take longer to speed up? The RED Truck – 30,000kg It goes back to the greater the mass – the greater the resistance to acceleration.

8. F m a Newton’s 2nd Law of Motion - Continued Newton’s 2nd Law of Motion can be expressed in an equation: Force = Mass X Acceleration F = ma divide multiply Force units = kg.m/s2 OR Newton Mass units = kilograms (kg) Acceleration units = m/s2

9. Newton’s 2nd Law of Motion - Continued Problem: What force is exerted on a 1000kg car accelerating at a speed of 15m/s2? Step 1 Read the problem. Draw a picture. 1000kg 15m/s2

10. 1000kg 15m/s2 What force is exerted on a 1000kg car accelerating at a speed of 15m/s2? Step 2 Write down what you know. What are you trying to find? ? F = M = 1000kg A = 15m/s2

11. 1000kg 15m/s2 Substitute Formula Answer What force is exerted on a 1000kg car accelerating at a speed of 15m/s2? Step 3 Set up the formula. ? F = F = ma M = 1000kg A = 15m/s2

12. 1000kg 15m/s2 Formula Substitute Answer What force is exerted on a 1000kg car accelerating at a speed of 15m/s2? Step 4 Substitute the numbers. Solve. Box Answer with Units. F = 15,000N F = 15,000 kg.m/s2OR F = 15,000 N F = ma M = 1000kg F = 1000kg x 15m/s2 A = 15m/s2

13. Do problems 1-3 in your notes.

14. Newton’s 2nd Law of Motion - Continued The acceleration for any object moving under the sole influence of gravity. Any moving object being acted upon only by the force of gravity is said to be "in a state of free fall." Characteristics of Free-Falling Objects: • do not encounter air resistance. • (on Earth) accelerate downwards at a rate of 9.8 m/s2.

15. Assuming that the position of a free-falling ball dropped from a position of rest is shown every 1 second, the velocity of the ball shown to increase as the time increases. What relationship do you notice about the distance per every 1 second? So…what type of acceleration does the ball have? Positive or Negative. Let’s Look at a Diagram

16. Vf - Vi a = t Remember the formula to find acceleration?

17. Let’s Look at a Problem What is the velocity of a rubber ball dropped from a building roof after 5 seconds? Step 1 Read the problem. Draw a picture. Step 2 Write down what you know. What are you trying to find? Vf = ? Vi = 0 m/s t = 5 s a = 9.8 m/s2

18. 49m/s= Vf – 0m/s 9.8m/s2 = Vf – 0m/s + 0m/s + 0m/s = Vf - Vi Vf - Vi a= 5 s a = t t What is the velocity of a rubber ball dripped from a building roof after 5 seconds? Step 3 Set up the formula. Step 4 Substitute the numbers. Solve. Box Answer with Units. Formula Substitute Answer 49m/s= Vf

19. Do problems 4 & 5 in your notes.

20. Newton’s 3rd Law of Motion Law of Action / Reaction Third Law basically states that…to every ACTION there is an equal and opposite REACTION. Action/Reaction forces act in PAIRS.

21. Newton’s 3rd Law of Motion - Continued In this example, when the lady is walking, her feet push against the ground while the ground pushes against her feet. Thus action/reaction – pair is the feet and ground pushing off of one another.

22. Newton’s 3rd Law of Motion - Continued Another example: Let’s think about this one…what are the pairs of forces that are acting against each other in order for the shuttle to launch?

23. MOMENTUM Property of a moving object because of its mass and velocity. An increase in mass or velocity causes an increase in momentum.

24. P m v Momentum can be calculated with the following formula: Momentum = Mass X Velocity P = mv Units for Momentum are kg.m/s

25. Formula Substitute Answer Problem: Find the momentum of an 7.2kg rock that is rolling down a hill with a velocity of 3.0m/sec. Step 3 Set up the formula. Step 1 Read the problem. Draw a picture. Step 4 Substitute the numbers. Solve. Box Answer with units. Step 2 Write down what you know. What are you trying to find? P = 21.6kg.m/s 7.2kg m = P = mv P = 7.2kg x 3.0m/s P = 21.6 kg.m/s v = 3.0 m/s Units, units, units!

26. Do problems 6 & 7 in your notes.

27. Law of Conservation of Momentum • In the absence of external forces applied to a system, the total momentum cannot change. • m1 v1 = m2v2

28. Do problems 8 & 9 in your notes.