iesc110

Motion and Force

  • Chapters 8 and 9 Overview

    • Discussion on motion of objects and force as a cause of motion.

    • Forces change speed or direction of motion.

    • Objects fall towards Earth and planets orbit the Sun due to gravitational forces.

Gravitational Force

  • Introduction to Gravitation

    • Chapter focuses on gravitation and the universal law of gravitation.

    • Study of how gravitational force affects the motion of objects on Earth.

    • Weight of a body varies in different locations due to gravitational pull.

    • Concept of buoyancy in liquids analyzed.

  • Newton's Apple

    • The anecdote of Isaac Newton and the falling apple.

    • Thought process: If Earth attracts an apple, it must also attract the moon.

    • Reflection on the moon's orbit: it falls towards Earth due to gravitational attraction but appears to move in a circular path due to centripetal force.

Universal Law of Gravitation

  • Statement

    • Every object in the universe attracts every other object.

    • The force of attraction is proportional to the product of their masses and inversely proportional to the square of the distance between them.

    • Mathematically expressed as:

      F \propto \frac{m_1 m_2}{d^2}

      F = \frac{G m_1 m_2}{d^2},where G is the gravitational constant.

  • Centripetal Force

    • When an object moves in a circular path, it experiences centripetal force directed towards the center of the circle.

    • Without centripetal force, the object moves in a straight line (tangential to the circular path).

Newton: The Father of Gravity

  • Biography

    • Isaac Newton's life span: 1642 – 1727; influential theorist in science.

    • Attended Cambridge University. Incident with falling apple during the plague year inspired his work on gravity.

  • Contributions

    • Formulated laws of motion and law of gravitation.

    • Developed calculus.

    • Unified various scientific contributions into a coherent framework during the scientific revolution.

Applications of Gravitational Law

  • Examples of Gravitational Effects

    • The force binds us to Earth, governs the moon's motion, controls planetary orbits around the Sun, and explains ocean tides.

  • Free Fall

    • Objects fall towards Earth due to gravitational force alone, termed as free fall.

Measuring Gravitational Force

  • Calculation of 'g'

    • 'g' can be calculated using values of Gravitational constant (G), mass of Earth (M), and radius of Earth (R).

    • Accepted value of g = 9.8 m/s2 on Earth's surface.

Weight vs. Mass

  • Definitions

    • Mass is constant regardless of location; it measures inertia.

    • Weight is the force acting on a mass due to gravity and varies with location.

    • Weight formula:

      W = m \times g

  • Weight on the Moon

    • An object's weight on the moon is less due to weaker gravitational pull (1/6 of that on Earth).

    • Example: A 10 kg object weighs 98 N on Earth and only about 16.3 N on the Moon.

Buoyancy and Pressure

  • Understanding Buoyancy

    • Buoyant force: upward force acting on objects submerged in a fluid.

  • Archimedes’ Principle

    • A body immersed in fluid experiences an upward force equal to the weight of the fluid displaced by it.

  • Factors Influencing Floating/Sinking

    • Objects with density less than the fluid float; greater density objects sink.

Pressure in Fluids

  • Definition of Pressure

    • Pressure = Thrust / Area, with SI unit as Pascal (Pa).

    • Applications include buoyancy in fluids and designing ships/submarines.

Summary of Key Learning Points

  • Universal law of gravitation applies to how objects in the universe interact irrespective of their distance.

  • Gravitational force is fundamental to understanding motion both on Earth and in space.

  • Key concepts include the distinctions between mass and weight, the significance of buoyancy, and the overall impact of gravitational theory on scientific thought.

robot