This set covers Abeka Physics Chapter 8: "Forces in Nature" (pages 110-129).

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  • Principia Mathematica

    book by Isaac Newton that presented three laws of motion that still serve as the conceptual foundation of physics


    term for a body's tendency to maintain its velocity, or a resistance to any change in velocity

    straight line, speed

    A body in motion tends to move in a ____ ___ at a constant ____.


    term for any push or pull on an object


    A body at rest tends to stay at rest, unless acted upon by an outside ___.


    term for the force that acts against every object in motion in the opposite direction to slow it down, or the resistance arising when an object moves through a medium or across a surface

    Newton's first law of motion

    the law that states that a body in motion tends to move in a straight line at a constant speed, and a body at rest tends to stay at rest, unless acted upon by an outside force

    F = ma

    equation for Newton's second law of motion

    inertial mass

    term for rest mass


    term for the force exerted on an object's mass by the earth's gravity

    Fw = mg

    equation for weight

    Newton's third law of motion

    law that states that every action has an opposite and equal reaction


    Forces always occur in action-reaction ____.


    Action and reaction are always opposite, equal, and along the same ___.


    ____ is caused by unbalanced forces acting on the same object.

    static friction and kinetic friction

    two types of friction

    kinetic friction

    term for an object's resistance to sliding

    static friction

    term for an object's resistance to start sliding


    True or False: Kinetic friction is dependent on the area of contact between the surfaces.


    True or False: Kinetic friction is dependent on velocity.


    Kinetic friction on a horizontal surface is proportional to the ____ of the moving object.

    normal force

    term for the force of a surface against the weight of an object


    The normal force always acts _____ to a surface.


    True or False: Rough surfaces produce more friction than smooth surfaces.


    term for any part of a machine that supports a moving part

    minimizing roughness; choosing suitable materials; lubricating; and rollers and bearings

    four methods of reducing friction on a surface

    strong force, electromagnetic force, weak force, and gravitational force

    the four fundamental forces of nature (from strongest to weakest)

    strong force

    the strongest of the four fundamental forces that holds an atomic nucleus together

    electromagnetic force

    the fundamental force that exists only between electrically charged bodies, binds the electrons of an atom to the nucleus, and causes an atom to resistance the penetration of its space by another atom

    weak force

    the fundamental force responsible for certain particle interactions in the radioactive decay of atomic nuclei

    gravitational force

    the weakest of the fundamental forces that exists between any two bodies of matter; attracts, but does not repel; and holds the moons, planets, and stars in their orbits

    electromagnetic force and weak force

    two fundamental forces that might be basically different expressions of the same force


    term that means "earth-centered"


    Greek astronomer who created a geocentric model of the solar system in the second century A.D.


    The _____ ("sun-centered") model of the solar system has become the foundation of modern astronomy.

    Nicolaus Copernicus

    sixteenth century Polish astronomer who proposed that sun was the center of the solar system

    law of orbits, law of areas, and law of periods

    Johannes Kepler's three laws of planetary motion

    law of orbits

    law that states that the orbit of every planet has the shape of an ellipse and that the two foci of each planetary orbit are relatively close together

    law of areas

    law that says that as a planet gets farther away from the sun, the distance traveled by the planet must shorten and the velocity must decrease


    term for the farthest position from the sun in a planet's orbit


    term for the closest position to the sun in a planet's orbit


    term for the time required for any planet to complete one orbit about the sun

    law of periods

    law that says that for any planet, the square of the period of revolution is proportional to the cube of the average distance from the sun


    term for the science of mechanics that seeks merely to describe motion by describing its causes


    term for the science of mechanics that seeks to explain motion by describing its causes

    universal law of gravitation

    law that states that the same kind of force exists between any two masses, regardless of size; specifically, that they are mutually attracted by a force governed by the proportionality


    term for the attractive force that exists between any two masses


    True or False: 'Gravitation' and 'gravity' do not mean the same thing.


    As the distance from the earth's center of mass increases, ____ diminishes.

    static equilibrium

    An object that remains at rest within earth's gravitational field is said to be in ____ _______.

    center of gravity (CG)

    term for the one spot that represents the combined effect of gravity's influence on all the particles in an object

    stable equilibrium

    An object in ____ _____ is not easily tipped over.

    unstable equilibrium

    An object in ____ _____ is upset at the slightest disturbance.

    neutral equilibrium

    An object in ____ _____ can be overturned without changing the height of its center of gravity.


    term for the state in which an object's center of gravity is unsupported, and the point where the force of gravity is effectively applied is free to move in the direction of the applied force

    multiple suspensions

    the simplest way of determining the center of gravity for irregular objects

    center of mass

    term for the point in an object that describes the combined effect of all the individual particles of mass

    gravitational field

    Scientist have sought to remove the mystery from gravitation by imagining that each object sets up a _____ ____ in which other objects are impelled to move by a force in the object's surrounding space.

    gravitational field strength

    term for the acceleration of an object in free fall (the gravitational force per unit mass)

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