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1. Newton’s Second Law of Motion

2. Newton’s second law of motion Objectives: You will be able to: State Newton’s second law and describe how it is related to motion Explain how Newton’s second law describes how acceleration is directly proportional to the net force, and inversely proportional to mass. Solve problems using Newton’s second law
3. Recall that: 1)An unbalanced force can cause an object at rest to move , changing its velocity creating an aceleration (rf ch2, section 2) 2) An object at rest or moving at constant speed will remain if the net force is equal to zero
4. In other words
5. Newton’s second law of motion Look at the figures and answer the below questions: Which figure (s) represent accelerating objects? In which direction. Which figure represent the object having the highest acceleration? Conclude.
6. Force and acceleration Look at the following diagrams and answer the below questions: Which objects are accelerating? Which objects are not accelerating? --------------------------------------------- Which object are subject to an unbalanced force? --------------------------------------------- 3. Which objects are subject to a net force equal to zero? --------------------------------------------- Conclude ----------------------------------------------------
7. Conclusion A force can accelerate an object in the same direction of the force. Acceleration is directly proportional to force ( example: if force is multiplied by two, acceleration would be multiplied by two). Application: A net force of 200 N to the right accelerates an object of 2m/s² . Find the acceleration of this object if: Net force = 400 to the left Net force= 300 N to the right For each of the following, state if the object would be accelerating. If yes, write in which direction. Object 1: F1= 400 N upward, F2= 600 N downward. Object 2: F1= 400 N upward, F2= 400 N downward. Object 3; F1= 400 N upward, F2= 400 N downward, F3= 200 N to the left.
8. Newton’s second law of Motion Which object would be have a higher acceleration if they are subject to the same force? ---------------------------------- Conclude ---------------------------------- Mass and acceleration Look at the figure below
9. Conclusion Objects with higher masses would have lower acceleration if subject to the same force. This can be explained by the fact that big masses have high inertia so they have greater tendency to resist any change in motion. (Rf.to chapter 2 section 3) Acceleration is inversely proportional to the mass ( example if mass is multiplied by three, acceleration would be divided by three).
10. Newton’s second law of motion We can summarize that acceleration is: Directly proportional to the force applied Inversely proportional to the mass of the object. In other words, we can write: Acceleration(m/s²)= force (N)/mass (kg)
11. Newton’s second law of motion Newton’s second law of motionstates that the acceleration of an object is in the same direction as the net force on the object, and that the acceleration can be calculated from the following equation:
12. Newton ‘s second law of motion Now can you calculate the acceleration of the car in the figure at the right ? Application : Solve questions 1- 9 from the worksheet Answer: Acceleration= force/mass= 50/1,000= 0.05 n/s²
13. Do Not Forget If forces are balanced (net force =0),an object at rest stays at rest, an object with a constant velocity keeps its constant velocity. (acceleration= 0) This is Newton’s first Law of Motion. If Forces are unbalanced (net force=0), an object will change aits velocity and have an acceleration in the same as the direction of the force and: Acceleration=Force(N) (m/s²) Mass (kg)
14. For next time Solve questions TB page: 69 no:1-4 74 no: 1,2,6 &7 Download powerpoint presentation from wikispaces System wide quiz 2 on Sunday 20/11/2011 Lessons included: Ch: 1: section 1.3 Ch.2: section 2.1 section 2.2 Good Luck !!!