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.