[Async-2024-25] SPH4 ...

UNIT FOCUS

Understand and apply Newton's Laws of Motion, analyze forces using free-body diagrams, solve problems involving friction, inclined planes, and circular motion, and apply concepts to real-world situations.

KEY CONCEPTS TO STUDY

1. Newton's Laws of Motion

• 1st Law (Inertia): Objects remain at rest or in unifrom motion unless acted upon by a net force.
• 2nd Law: Net force = mass x acceleration (\(F_{net}=ma\))
• 3rd Law: For every action, there is an equal and opposite reaction.

2. Free-Body Diagrams (FBDs)

• Practice drawing FBDs for objects on horizontal and inclined planes.
• Include all forces: gravity (\(F_g\)), normal force (\(F_N\)), applied force (\(F_a\)), friction (\(F_f\)), tension (\(T\)), etc.

3. Types of Forces

• Gravitaional Force: \(F_g=mg\)
• Normal force: Perpendicular to the surface
• Friction: 
• Static: \( F_s \leq \mu_sF_N \)
• Kinetic: \( F_k \leq \mu_kF_N \)
• Tension and Applied Forces

4. Inclined Planes

• Break gravity into components:
• Along the incline: \( F_{||}=mgsin \theta \)
• Perpendicular to incline: \( F_{⊥}=mgcos \theta \)
• Normal force and friction depend on angle.

5. Circular Motion

• Objects moving in a circle at constant speed have centripetal acceleration:
• \( a_c= \frac{v^2}{r} \)
• \( F_c= \frac{mv^2}{r} \)
• Centripetal force is not a new force; it's the result of another (tension, gravity, friction).

6. Friction

• Know how to calculate and compare static and kinetic friction.
• Understand the role of friction in circular motion and on ramps.

PROBLEM-SOLVING SKILLS

• Analyzing forces in 1D and 2D motion
• Applying Newton's laws to real-world systems (e.g., ramps, elevators, rope tension)
• Solving for unknowns: acceleration, force, friction, velocity
• Interpreting FBDs and breaking vectors into components
• Applying concepts to conceptual and numerical equations

COMMUNICATION TIPS

• Clearly explain concepts using scientific language
• Justify answers logically (e.g., why friction increases or decreases)
• Use diagrams to support explanations
• Practice full-sentence explanations for multi-step problems

SAMPLE REVIEW QUESTIONS

1. A 10.0 kg box is pulled across a floor with a force of 40 N at \(25^o\) above the horizontal. The coefficient of kinetic friction is 0.3. What is the box's acceleration?

2. A 1200 kg car rounds a curve of radius 60 m at a speed of 18 m/s. Will the car skid if \( \mu_s=0.25 \)?

3. Draw a complete FBD for a sled being pulled uphill with a rope. Include all force components.

4. In your own words, describe the motion of an object that experiences a net force of zero.

5. Compare and contrast static and kinetic friction with real-life examples.

6. You are helping to design a driver education course. You are asked to explain how Newton's three laws apply when a car:

• starts moving from rest,
• travels at a constant speed, and
• comes to a stop.

Write a short paragraph explaining how each of Newton's three laws of motion is demonstrated during these phases of motion. Be sure to use proper terminology and provide real-world reasoning.

Tip: One paragraph per law is a good structure. Use terms like "net force", "acceleration", "inertia", and "action-reaction" as appropriate.

TEST DAY REMINDERS

• Make sure to have a scientific calculator
• You may use your notes and handouts (open book)
• Show all work for calculation questions
• Label diagrams and state final answers clearly