Newtons First Law of Motion

First Law of Motion

  • Quote by Isaac Newton: "If I have seen further it is by standing on ye shoulders of Giants."

  • Prepared by: Engr. Jhoneil Viernes, LPT

Law of Inertia

  • Concept: Understanding inertia and its significance in motion.

  • Goals:

    • To comprehend inertia and its application in real-world contexts.

    • To differentiate inertia from other forces in motion.

Key Terms to Recall

  • Net Force: The overall force acting on an object when all individual forces are combined.

  • Mass: A measure of the amount of matter in an object, which influences its inertia.

  • Friction: A force that opposes motion between two surfaces that are in contact.

Real-World Examples of Inertia

  • Scenario 1: When a jeepney (a type of transportation) suddenly stops, a passenger continues moving forward due to inertia.

  • Scenario 2: If the jeepney is at rest and suddenly accelerates, the passenger's body tends to stay at rest, causing a backward jolt.

Definition of Inertia

  • Inertia Explained: Inertia is the property of a body that resists changes in its state of rest or motion with a constant velocity. It is the natural tendency of an object to persist in its state of rest or uniform motion in a straight line.

  • Simplified Definition: "The tendency of an object to resist changes in its state of motion."

Activity Overview

  • Objective:

    1. Understand inertia.

    2. Illustrate inertia.

    3. Grasp Newton's laws of motion.

  • Materials:

    • Balls of various sizes

    • A glass

    • Coins

    • A sheet of paper

    • A straw

Activity Instructions

  1. Setup: Place a glass on a table and cover it with a sheet of paper.

  2. Execution: Place a coin on top of the paper and quickly remove the paper.

  3. Observation: Note the behavior of the coin to illustrate inertia and its effects.

Newton's Laws of Motion

  • General Context:

    • Newton (1643-1727) was an English scientist and mathematician recognized for discovering the law of gravity and establishing the three laws of motion published in his book Philosophiæ Naturalis Principia Mathematica (1687).

    • These laws explain the motion of objects within our everyday experiences.

Newton's First Law of Motion

  • Concept Summary:

    • A rolling ball will eventually stop due to external forces acting on it, such as friction.

    • This is illustrated in the contrast between Aristotle’s and Galileo’s understanding of motion.

  • Aristotle's View: The ball stops because it seeks its natural state (rest), requiring a force to maintain motion.

  • Galileo's View: The ball stops due to friction, and it would continue indefinitely in the absence of external forces.

  • Newton's Stance: Validating Galileo’s findings, he formulated the first law of motion:

    • Statement: "Every object will retain its state of motion (whether at rest or moving with constant velocity in a straight line) unless acted upon by a net force."

    • Real-World Example: Comparing a truck and a bicycle, the truck’s greater mass means it has more inertia and resists changes in motion more than the bicycle.

Implications of Newton's First Law

  • Rest of Objects: When in a state of rest, an object will remain in that state unless an external force acts upon it.

  • Motion of Objects: An object in motion continues in its current state (speed and direction) unless acted upon by a net force.

  • Practical Observation: This law explains why wearing seatbelts is crucial during car accidents:

    • In an accident, a passenger not wearing a seatbelt will continue moving at the car's speed until externally stopped by an obstacle (e.g., a windshield).

Summary of Inertia's Properties

  • Inertia and Mass Relationship: Inertia is directly proportional to mass; larger mass means greater inertia.

    • Example: A large train has significant inertia, making it hard to stop or accelerate compared to a small baby carriage, which has minimal inertia.

Further Applications of Inertia

  • Sumo Wrestling: The law of inertia plays a vital role as a larger fighter has greater mass and inertia, making it harder for opponents to displace him, while a smaller opponent may be more agile but easier to move.

  • Examples of Gravity and Inertia:

    • An egg at rest has inertia; once the supporting plate is removed, gravitational force causes it to fall, demonstrating the interplay of inertia and gravity.

Guide Questions on Inertia

  • 1. Is inertia a force?: No, it is a property of matter. It does not exert force but indicates an object's resistance to change.

  • 2. Mass and Inertia Relation: Mass measures the amount of inertia an object possesses; the larger the mass, the more inertia.

  • 3. Effect of Gravity: If the gravitational force between the sun and its planets ceased, planets would travel in straight-line paths.

  • 4. Jumping Example: Jumping up does not alter your horizontal velocity (i.e., 30 km/s relative to the sun); you and the wall move at the same speed pre- and post-jump.

Seatwork and Application Exercises

  • POP QUIZ Scenario #1: A passenger claims injury due to a suitcase flying towards him during sudden braking of the bus. Necessary considerations include inertia's role in both events—the suitcase continues moving forward due to inertia until stopped by an external force.

  • Scenario #2: Ariel, a good racer, must choose between two competitions with overlapping schedules, with considerations on inertia affecting decisions and proficiency in both races.