Newton's Second Law of Motion

1. Do Now 2.10.14 Grab a Calculator If a table is being pushed across the floor at 20N and friction is 5 N. What is the net force on the chair? Newton's Second Law of Motion Week of 2.10.14

2. The acceleration of an object is directly proportional to the netforce acting on the object, in the direction of the net force, and is inversely proportional to the mass of the object - in short: A = net force or F = ma mass - symbols: a = acceleration Fnet = force m = mass Newtons 2nd Law

3. A boy pushed forward a cart of groceries with a total mass of 40.0 kg. What is the acceleration of the cart if the net force on the cart is 60.0 N?

4. An automobile with a mass of 1200 kg accelerates at a rate of 3.0m/ s2 in the forward direction. What is the net force acting on the automobile? • A 25 N force accelerates a boy in a wheelchair at 0.5m/s2. What is the mass of the boy and the wheelchair? You Try!

5. A = F/m 60.0 N = 1.50 m/s2 40.0 kg • F = ma 1200 kg x 3.0 m/s2 = 3600 N • M = F/a 25 N = 50 kg 0.50 m/s2 Answers

6. Q: Would it be easier to lift a huge truck on the Earth or on the Moon? Weight vs. Mass

7. Q: Would it be easier to lift a huge truck on the Earth or on the Moon? A: On the moon, when you lift an object you are dealing with weight, since weight is the gravitational pull on the most massive body, and the moon has less gravity than the earth Weight vs. Mass

8. Weight : The force of gravity acting on an object • Mass: the measure of inertia on an object Weight vs. Mass

9. Weight = Mass x Acceleration due to gravity • W= mg • What is the acceleration of gravity? Weight vs. Mass

10. What is the weight of a person with a mass of 29 kg on earth? If the acceleration of gravity on Mars is 3.7 m/s/s what would be the weight of this person on Mars? Practice Problems

11. The gravitational pull on an unknown planet in 20 m/s/s. Ms. Miller goes to visit the aliens on this planet. If her mass is 40 kg on earth what would her weight be on this new planet? • A person weighs 56 kg on earth. What is their mass? You Try!

12. If you would like to earn 15% back on your last Exam this is what you can do. • Pick up an Exam • Take it home • Answer the questions • YOU MUST DO IT ON A SEPARATE SHEET OF PAPER • YOU MUST TELL ME WHY YOU GOT IT WRONG THE FIRST TIME!!!!! • If you do not do what it bolded and underlined you will not get credit.

13. Rewrite the questions in your notes • Underline what the question is asking for • Write the equation you will be using • Solve Practice Problems

14. What is the acceleration of a helicopter with a mass of 5000 kg and a force of 10,000N? • A boy kicks a soccer ball that is at rest and it reaches a speed of 10 m/s 1 second after being kicked. What is its acceleration? Practice Makes Perfect!

15. During a test crash an airbag inflates to stop the dummies forward motion. The dummy has a mass of 75 kg. If the net force is 825 N towards the rear of the car, what is the dummies deceleration? Practice Makes Perfect!

16. A boy has a weight of 220 kg on a planet with a gravitational pull of 36 m/s/s. What would his weight be on Earth? • A car is going 90 km/hr at a constant speed. How far will he travel in 3 hours? Practice Makes Perfect!

17. A bicycle takes 8 seconds to accelerate at a constant rate from rest to a speed of 4 m/s. If the mass of the bicycle and rider together is 85 kg, what is the net force acting on the bicycle? (hint: first calculate acceleration) Practice makes Perfect!

18. Speed • Acceleration • Mass vs Weight • Net Force • You can make an equations sheet! • One page ONLY equations Test Thursday

19. Action Reaction Forces - whenever on object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. ex. produces motion: car tires push backwards against the road the road pushes forward against the car tires ex. no motion: hand pushes against the wall the wall pushes against your hand Newtons Third Law

20. if we drop a sheet of tissue paper in front on the heavy weight champion of the world and challenge him to hit it in midair with 50 lbs of force, his best punch couldn’t even come close Why? - a force is not a thing in itself but makes up an interaction between itself and another (system) - the action force and the reaction force - net force only equals 0 when force are equal and opposite

21. Q: One cold and rainy day, you car battery is dead and you must push the car to get it started. Why can’t you push the car by remaining comfortably inside pushing against the dash?

22. Q: One cold and rainy day, you car battery is dead and you must push the car to get it started. Why can’t you push the car by remaining comfortably inside pushing against the dash? A: Pushing again the dash creates a internal force to the system, in order to accelerate the car you must have an external force to the system

23. Definition • a quantity defined as the product of an object’s mass and its velocity • Formula M = m x v p = m x v • Units Kg x m/s Momentum

24. Define Momentum • What is the formula? • What are the units? • Why do these units make sense? Do Now!!!!

25. Which object has more momentum: a car traveling at a speed of 10 km/hr or a baseball pitched at 150 km/hr. Explain your answer Think about it!

26. What is the momentum of an 0.30 kg blue jay flying at 17 m/s? • What is the mass of the train car moving at 14 m/s with a momentum of 140 kg-m/s? of the car moving at 10 m/s with a momentum of 100kg-m/s? What is the total momentum of the system? Practice Makes Perfect!

27. Notes for this week (40 points) • Participation (20 points) Tribal Council