Mr. Rogers' AP Physics C: Mechanics (With IB Physics Topics) Objectives

Syllabus 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter
Kinematics (1)
Vector Addition (2)
Projectile Motion (3)
Newton's Laws (4)
 

Chapter 5: The Laws of Motion

AP Physics C Newtonian Mechanics: B. Newton's laws of motion Approx 10%, cumulative 28%
    1.Static equilibrium (first law) 
    2.Dynamics of a single particle (second law) 
    3.Systems of two or more bodies (third law) 

 

Practice Test Study Guide

Objectives

Essential Question: Is mass in physics the same thing as the amount of matter present?

Newton's 3 Amazing Laws

  1. Explain inertia and its relationship to mass. (mass = linear inertia)

  2. Explain what is meant by an inertial frame of reference (Serway p.114).

  3. Solve problems with Newton's 1st law (the bunny principle).

  4. Explain Newton's second law (F = ma). This is actually a special case of Newton's 2nd Law. It assumes that the net force and mass are both constant. We have to introduce momentum to write the most general case.

  • F = net Force or sum of the forces
  • m = linear inertia
  • English version: net Force is directly proportional to acceleration
  1. State Newton's 3rd law in 3 ways.

  • Serway p.120
  • Can't touch without being touched
  • Forces always appear in pairs acting in opposite directions on 2 different objects.
  1. Solve problems using Newton's 3rd law.

Homefun (formative/summative assessment): Read 5.1 to 5.5

Read: Insultingly Stupid Movie Physics

Chapter 5, Inertia and Newton's first Law: Why Blowing Up a Spacecraft is a Bad Idea.  pp 67 - 83

Chapter 6, Newton's Third Law: That Special Hollywood Touch, pp 83 - 99

Relevance: Newton's laws revolutionized science and ushered in a new era of technological development. Even today over 300 years later they are the foundation of modern engineering.

 

Activities

Lesson 1

Pre-assessment: Use the internet to answer questions 21 - 26 on the Basic Physics Savvy Quiz 

Key Concept: Newton's laws, free body diagrams.

Purpose: Solving acceleration problems using free body diagrams. 

Interactive Discussion: Objectives. What would the world be like if Newton's first law were turned off. In other words, what if motion required a net force to keep it going. A bus hits a bug. Which has the higher force a bug or a bus? Draw free body diagrams.

In Class Problem Solving:  

  1. Bob weighs himself on the elevator.
  2. Bob pulls himself upward using  a pulley and harness.
  3. Jane drives her boat.

 

Essential Question: If forces always come in pairs, how can anything move?

 FBDs, g, and Acceleration

  1. Identify action/reaction pairs of forces.

  2. Draw free body diagrams.

  • Generally shows the object as a square or a dot.
  • Shows only forces from the outside acting on the object. The forces are shown touching the object.
  • Never shows forces the object creates on the outside world.
  1. State 3 ways "g" can be defined.

  • Acceleration of a free falling body with no air resistance on planet Earth = 9.80665 m/s2
  • Unit of acceleration. 1.0 g = 9.80665 m/s2
  • Gravity-field strength typically used for calculating weight force. On planet Earth g = 9.81 m/s2
  1. Calculate the weight force acting on an object: Fw = mg Note that the g in this case is the strength of the gravity field.

  2. Correctly identify normal forces. Normal forces are forces generated when one surface presses against an object. Normal forces are always perpendicular to the surface causing them.

formative/summative assessment: vocaulary quiz

Essential Question: When you step on a bathroom scale, which force is the scale actually measuring?

Elevator Problems

  1. Explain which external force acting on a person causes the sensation of weight. The normal force

  1. Solve elevator problems.

  • "g" is a gravity-field strength vector not an acceleration.
  • "g" is negative because it points downward.
  • Fw = mg
  • The scale the person stands on indicates the normal forc not the weight or gravity force
  1. Solve elevator type problems in a horizontal dimension. These have 2 opposing forces in the horizontal dimension. The equation ends up being identical to the elevator problems.
  1. Solve 2 cable elevator problems.

Here the person can be visualized as pulling himself up using a rope and pulley.

As is often true, the trick for solving the problem is drawing a correct FBD.

 

Homefun (formative/summative assessment): Read 5.6, prob. 1, 3, 33, 51 pp. 128-131

Read: Insultingly Stupid Movie Physics
Chapter 10, Acceleration and Newton's Second Law: How to get started, Use the Breaks, or Change Direction Hollywood Style, pp 147 - 163

Relevance: Most engineering majors will be required to take a dynamics course based primarily on Newton's Second Law. Dynamics analysis is critical to machine design, an important issue for mechanical engineers .

 

Lesson 2

Key Concept: Free body diagrams (FBD)

Purpose: Enable one to identify the forces that belong in  a Newton's second law equation

Interactive Discussion:  What causes the sensation of weight?

Video Clip: Show a video clip of the rocket sled ride in Indiana Jones. Assume Jones weighs 180 lb and is subjected to 10 g of acceleration as the sled speeds up and 40 g acceleration while stopping. What would be the size of the force between Jones and his seat while speeding up? What size force would be required to hold Jones on the sled while slowing down?

In Class Problem Solving: elevator problems

  1. Bob stands on a scale in the elevator
  2. Bob's boat has water resistance.
  3. 2 cable elevators

Essential Question: Can metacognition questions be used to start a problem as well as evaluate its answer?

Pushing, Pulling, and Cliff Hangers

  1. Find the normal force between objects when one object is pushing another.

  2. Find the tension in the rope when one object is towing another.

  3. Solve Jurassic Park type suspended bus problems.

 

Metacognition Problem Solving Principle: A teacher can guide a student to the solution of a complex problem merely by asking questions, but first the student must first learn to answer rather than simply follow the teacher's instruction. Ultimately, the student can solve problems without the teacher by learning to ask himself or herself the questions. Problem solving is about asking questions.

Homefun (formative/summative assessment): Read 5.6, prob. 31 pp. 128-131

 

Lesson 3

Key Concept: Free body diagrams (FBD)

Purpose: Enable one to identify the forces that belong in a Newton's second law equation

Interactive Discussion:  Objectives.

Video Clip: Show a video clip of the bus hanging scene in Jurassic Park

In Class Problem Solving:

  1. Towing problem
  2. Pushing problem
  3. Jurassic Park problem
Mini-Lab Physics Investigation (Requires only Purpose, data, and conclusion)
Title Analysis of an Air Track Slider Accelerated by a hanging weight
Purpose Determine if simple mathematical models can predict the behavior of an air track slider accelerated by a hanging weight.
Overview
  1. Place the slider on the air track.
  2. Attach a string to the slider and thread it through a pulley at the end of the air track.
  3. Attach a weight to the end of the string so that it hangs over the table.
  4. Set up the photogate to measure velocity after the slider has traveled some distance from a rest position.

By knowing the final velocity and distance the slider's acceleration can be calculated. Compare this acceleration to one calculated from theory. Assume the pulley at the end of the track along with the string pulling the cart are frictionless and massless.

Data, Calculations Calculate a % difference between the measured and theoretical acceleration
Questions, Conclusions
  1. What is the maximum possible acceleration of the cart?
  2. If your acceleration values are higher than the maximum possible, what is the likely source of the error? (Do NOT claim it's measurement error.)
  3. Why should the measured value be less than the theoretical one?
Resources/Materials: Air track and slider. Photogates computer system set up with Vernier LabPro software and Lab Pro units
Essential Question: Can we use redefining the x, y axis as a problem solving strategy?

Objects on Slopes

  1. Find the normal (Fwn) and parallel (Fwp) components of the weight force (Fw) for objects on a slope that makes an angle of with the horizon β.

Fwn = Fw cosβ

Fwp = Fw sinβ

 

  1. Find the angle of the slope where the normal component of weight exceeds the parallel component.

  2. Solve for acceleration of objects on a slope (zero friction).

 

Homefun (formative/summative assessment): 22, 24 pp.128-131

Relevance: Components on a slope is the first step in analyzing numerous real world problems from ramps for unloading cargo to 4WD vehicle climbing performance

.

Lesson 4

Key Concept: Normal and parallel components on a slope

Purpose: Enable one to solve slope problems

Derivation: weight components on a slope.  

In Class Problem Solving:

  1. Toto on a slippery slope.
  2. Tension in Toto's collar

Group problem solving: Plot the acceleration, normal, and parallel forces vs angle. Draw conclusions from the plots.

  1. Box on a slope with angle changing
  2. Box on horizontal ground being pushed with angle changing.
  3. Box on horizontal ground being pulled with angle changing.

Resources/Materials:

Formal Physics Investigation

Title Measurement of g Using an Air Track
Category Newton's Laws
Purpose Measure g using an air track
Models kinematic equations, F = ma (Note: if kinematic equations can be used, then what do you know about the slider's acceleration?)
Overview A slider can "fall" down the slope of an air track set at an angle with respect to the horizontal. You are to devise an experiment for determining the value of g by using the air track and other equipment provided.
Safety Issues Air track motors can overheat if the air inlet is blocked.
Equipment Limitations Air tracks an their sliders are much more delicate than they look. Do NOT drop or strike them
Resources/Materials: Air track and slider. Photogates computer system set up with Vernier LabPro software and Lab Pro units
Essential Question: What do civil engineers do? Why did the Twin Towers collapse?

Statics (the first half of the story)

  1. State the force conditions required for static equilibrium.

SFx = 0, SFy = 0, SFz = 0

  1. Solve static equilibrium, cable problems. (buzzard problem)

  2. Solve static slope problems.

 

Homefun (formative/summative assessment): prob. 21,  23, 27, 35 pp. 128-131

Relevance: Statics calculations are the first step in designing structures, an importance issue for both civil and mechanical engineers.

Lesson 5

Key Concept: Static equilibrium

Purpose: Solve static cable problems.

Interactive Discussion:  Can the tension in a rope be greater than a perpendicular force exerted in its center it?

In Class Problem Solving:

  1. Buzzard problem
  2. Stop light problem
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Insultingly Stupid Movie Physics is one of the most humorous, entertaining, and readable physics books available, yet is filled with all kinds of useful content and clear explanations for high school, 1st semester college physics students, and film buffs.

It explains all 3 of Newton's laws, the 1st and 2nd laws of thermodynamics, momentum, energy, gravity, circular motion and a host of other topics all through the lens of Hollywood movies using Star Trek and numerous other films.

If you want to learn how to think physics and have a lot of fun in the process, this is the book for you!

 

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now the book!


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