Lecture Notes: Newton's Laws of Motion

Introduction to Forces and Motion

• Topic: Understanding forces and why they cause acceleration.
• Reference Physicist: Isaac Newton.
• Key Resource: Newton's three laws from "Principia" (1687).

Newton's First Law: Inertia

• Definition: Objects in motion stay in motion, and objects at rest stay at rest unless acted upon by a force.
• Concept: Inertia is an object’s tendency to keep doing what it’s doing.
• Measurement: Mass is a measure of inertia.
  • Example: Bowling ball vs. beach ball.
• Net Force: Required to change motion or cause acceleration.

Newton's Second Law: Force and Acceleration

• Equation: F(net) = ma (Net force = mass x acceleration).
• Net Force: Sum of all forces; unbalanced forces lead to acceleration.
  • Example: Hockey puck on a frictionless surface.
• Gravity Example: A 5 kg ball accelerates due to gravity at 9.81 m/s^2.
  • Calculating Force of Gravity: F(g) = mg.
  • Weight is measured in Newtons.

Newton's Third Law: Action and Reaction

• Definition: For every action, there is an equal and opposite reaction.
• Normal Force: Force perpendicular to the surface.
  • Characteristics: Changes magnitude based on the force applied (e.g., grapes on foil).
• Real-life Application: Reindeer pulling a sleigh.
  • Ground push provides greater force than the sleigh's pull back.

Forces in Equilibrium

• Concept: Even moving objects can be in equilibrium if velocity is constant.
  • Example: Object moving at constant speed.

Problem Solving: Free Body Diagrams

• Purpose: Visualize forces acting on an object.
• Steps:
  1. Draw object outline and central dot.
  2. Label arrows for forces.
  3. Determine positive direction.
  • Example: Box on the ground vs. suspended box.

Tension Force

• Definition: Force in a rope or cable when it's pulled tight.
• Characteristics: Similar to normal force; changes with applied force.

Application: Elevator Example

• Setup: Lift with mass of 1000 kg and counterweight of 850 kg.
• Goal: Calculate elevator's acceleration when released.
• Process:
  1. Free body diagrams for lift and counterweight.
  2. Use Newton's laws to derive equations.
  3. Solve equations to find acceleration.
• Result: Safe acceleration at 0.795 m/s^2.

Conclusion

• Key Learnings: Newton’s three laws, inertia, net force, equilibrium, normal, and tension forces.

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