Dynamics Newton s Laws Lecture Notes

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Pre-AP Dynamics Newton s Laws Lecture Notes Name Targeted Skills for Newton s Laws (Lecture ONLY) 1. Identify and apply Newton s Laws of Motion to a variety of qualitative and quantitative problems.

Analyze position versus time, velocity versus time and acceleration versus time graphs for regions of zero and non-zero net force. 5. Solve dynamics problems. 6.

1 Pre-AP Dynamics Newton s Laws Lecture Notes Name Targeted Skills for Newton s Laws (Lecture ONLY) 1. Identify and apply Newton s Laws of Motion to a variety of qualitative and quantitative problems. 2. Identify: Gravitational Forces (F g ), Tension Forces (F T ) Normal Forces (F N ) and Frictional Forces (F f ). 3. Draw free body diagrams (FBD). 4. Analyze position versus time, velocity versus time and acceleration versus time graphs for regions of zero and non-zero net force. 5. Solve dynamics problems. 6. Identify when an object experiences kinetic and static frictional forces. 7. Interpret a force versus time graph for regions of static friction, kinetic friction, constant velocity, and accelerated motion. 8. Calculate the coefficient of kinetic and static friction 9. Solve friction problems. Newton s First Law of Motion Describe the motion of an arbitrary object sitting in the room. What s required to change an object s motion? Definition of Newton s First Law of Motion Law of Inertia Newton s Second Law of Motion What s required to change an object s motion? What results if an unbalanced force is applied to an object? Definition of Newton s Second Law of Motion Equation of Newton s Second Law of Motion

2 Free-Body Diagram Construction Horizontal / Vertical A jet plane is gliding at a constant elevation at a constant velocity. Draw the Free-Body Diagram of the forces acting on the plane. NO air resistance A jet plane is flying at a constant elevation at a constant velocity. Draw the Free-Body Diagram of the forces acting on the plane. Consider Air Resistance. A jet plane is flying at a constant elevation with an increasing velocity. Draw the Free-Body Diagram of the forces acting on the plane. Consider Air Resistance. A jet plane is flying at a constant elevation with a decreasing velocity. Draw the Free-Body Diagram of the forces acting on the plane. Consider Air Resistance. Free-Body Diagram Construction Inclined Parallelogram Method Problem #1 from the FBD Worksheet. Rules:

3 Example Problems - Horizontal / Vertical Problem FBD Solution Number 6 from FBD Worksheet G: m = 10 kg g = +9.8 m/s 2 U: F g No air resistance. Number 2 from FBD Worksheet G: m = 10 kg g = m/s 2 U: F T Number 3 from FBD Worksheet G: m = 30 kg g = m/s 2 U: F N Number 4 (Modified) from FBD Worksheet G: m = 20 kg g = +9.8 m/s 2 F applied = 25 N U: F f Sliding at constant velocity.

4 Example Problems - Inclined Hint Use Pythagorean Theorem. Problem FBD Solution Number 13 from FBD Worksheet G: m = 15 kg g = m/s 2 F T = 2F g U: F f Number 18 from FBD Worksheet G: m = 15 kg F f = ½F g U: F N Friction prevents rock from sliding. Number 16 from FBD Worksheet G: F N = 150N F T = 100 N U: m

005 kg coffee filter is dropped from rest from a height h above the floor. The filter falls for one second before reaching terminal velocity.

5 Example Problems Example #1 Fred and Wilma push a stalled car at constant velocity along level ground. If Fred and Wilma push the right with 395 N and 275 N respectively, what s the magnitude of the opposing force? Identify the opposing force. Example #2 A kg coffee filter is dropped from rest from a height h above the floor. The filter falls for one second before reaching terminal velocity. What s the filter s acceleration immediately after it s dropped? What s the filter s acceleration when it s falling at terminal velocity? What s the magnitude of the air resistance force while falling at terminal velocity? Draw a FBD of the falling filter sometime after it s released and before it reaches terminal velocity.

How fast is the buggy traveling after accelerating for 4 seconds?

6 Example #3 A dirt buggy has a mass of 575 kg. The buggy uniform accelerates from rest for 4 seconds and travels 35 meters. How fast is the buggy traveling after accelerating for 4 seconds? What s the buggy s acceleration? What net force is applied the buggy? Example #4 Two forces are applied to a 10 kg block. Calculate the block s acceleration if F 1 equals 15 N and F 2 equals 30 N.

Friction Example Problems Example #5 If you apply a 35 N horizontal force to slide a sleeping

7 Newton s Third Law Definition of Newton s Third Law of Motion Draw ALL forces. Identify action-reaction pairs of force? Explain how the horse-cart can move. Friction Example Problems Example #5 If you apply a 35 N horizontal force to slide a sleeping dinosaur across a frozen prehistoric lake at a constant velocity, what s the coefficient of friction between the dinosaur and ice?

Example #6 A sled of mass 50 kg is pulled along snow covered, flat ground. The static coefficient of friction is 0.30 and the kinetic coefficient of friction is 0.10. What does the slide weigh?

8 Example #6 A sled of mass 50 kg is pulled along snow covered, flat ground. The static coefficient of friction is 0.30 and the kinetic coefficient of friction is What does the slide weigh? What force will be needed to start the sled moving? What force is needed to keep the sled moving at a constant velocity? Once moving, what total force must be applied to the sled to accelerate it at 3.0 m/s 2? How long will it take for the sled to reach a velocity of 11.7 m/s? Example #7 Examine whether it s better to pull or push an object.

9 Graph of Motion Interpretation Scenario R.P. means Reference Point, i.e. the motion detector. AWAY from CONSTANT (constant velocity) Position vs. Time Graph Draw the shape of the graph. Sign (+, or zero) Slope is. Constant Changing Increasing Both Decreasing Velocity vs. Time Graph Draw the shape of the graph Sign (+, or zero) Slope is. Changing Constant Increasing Decreasing Both Acceleration vs. Time Graph Draw the shape of the graph NET FORCE (+, - or zero) CONSTANT (constant velocity) AWAY from DECREASING (slowing down) AWAY from INCREASING (speeding up) DECREASING (slowing down) INCREASING RATE (speeding up) then AWAY from the R.P. at a CHANGING RATE AWAY then CHANGING RATE

CHAPTER 4 TEST REVIEW -- Answer Key

CHAPTER 4 TEST REVIEW -- Answer Key AP PHYSICS Name: Period: Date: DEVIL PHYSICS BADDEST CLASS ON CAMPUS 50 Multiple Choice 45 Single Response 5 Multi-Response Free Response 3 Short Free Response 2 Long Free Response AP EXAM CHAPTER TEST