The combination of all forces acting on an object is called the
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net force
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When you hold a rock at rest in your hand, you are pushing upward on it with as much force as Earth's gravity pulls down on it. The net force would be
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zero on the rock
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The scientific unit of force is the newton--
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abbreviated N
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Tension is a
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stretching force
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Weight is the force of gravity
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acting downward on an object
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A vector is an arrow that
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represents the magnitude and direction of a quantity.
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A vector quantity is a quantity that needs both magnitude and
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direction for a complete description
-an example would be force
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A scalar quantity is a
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quantity that can be described by magnitude only and has no direction. -time, area, and volume are scalar quantities
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You can express the equilibrium rule mathematically as
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(funky backwards E letter)F=0
-e letter stands for the sum of
-f stands for forces
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Mechanical Equilibrium is a
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state wherein no physical changes occur; it is a state of steadiness
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Whenever the net force on an object is zero, the object is said to be in
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mechanical equilibrium
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What is the Equilibrium Rule?
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Whenever the net force on an object is zero, the object is said to be in mechanical equilibrium
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For a suspended object at rest, the forces acting upward on the object must be
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balanced by other forces acting downward to make the vector sum equal zero
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For an object at rest on a horizontal surface,
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the support force must equal the objects weight
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A support force is the upward force
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that balances the weight of an object on a surface. A support force is often called the normal force
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An upward support force is
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positive and a downward weight is negative
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-The weight of a book sitting on a table is a negative force
-The atoms squeeze
-The compressed atoms produce
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-that squeezes downward on the atoms of the table
-upward on the book.
-the positive support force.
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Objects at rest are said to be in
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static equilibrium
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Objects moving at constant speed in a straight line path are said to be in
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dynamic equilibrium
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Equilibrium is a state of
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no change
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An object under the influence of only one force
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cannot be in equilibrium
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Only when there is no force at all, or when two or more forces combine to zero, can
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an object be in equilibrium
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Both static equilibrium and dynamic equilibrium are examples of
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mechanical equilibrium
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The Parallelogram Rule
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to find the resultant of two nonparallel vectors, construct a parallelogram wherein the two vectors are adjacent sides. The diagonal of the parallelogram shows the resultant
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Resultant
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the sum of two or more vectors
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Combining vectors is simple when they are parallel.
-If they are in the same direction
-If they are in opposite directions
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-they add
-they subtract
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To find the resultant of nonparallel vectors
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use the parallelogram rule
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When applying the parallelogram rule to two perpendicular vectors that are equal in magnitude
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-the parallelogram is a square.
The resultant is root 2, or 1.414, times one of the vectors
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When an object is suspended at rest from two non-vertical ropes, there are three forces acting on it:
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1. a tension in the left rope,
2. a tension in the right rope
3. the object's weight.
The resultant of rope tensions must have the same magnitude as the objects weight.
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Aristotle
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the foremost Greek scientist
-studied motion and divided it into two types
--natural motion
--violent motion
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During Aristotle's time, natural motion on Earth was thought to be
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either straight or straight down: It was 'natural' for heavy things fall and fog very light things to rise
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Violent Motion
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was imposed motion and it was the result of forces that pushed or pulled
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The proper state of objects was thought to be one in rest, unless they were being
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pushed or pulled or were moving towards their natural resting place
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Copernicus reasoned that the simplest way to interpret astronomical observations was to assume
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that Earth and the other planets move around the sun
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Copernicus' idea of motion in space was extremely controversial at the time, because most people believed that
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Earth and the other planets move around the sun.
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Copernicus worked on his ideas in secret to escape
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persecution. At the urging of his close friends, he published his ideas
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Galileo argued that only when friction is present
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as it usually is, is a force needed to keep an object moving
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One of Galileo's greatest contributions to physics was
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demolishing the notion that a force is necessary to keep an object moving. A force is any push or pull.
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Friction
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the force that acts between materials that touch as they move past each other
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-Galileo found that a ball rolling on a smooth horizontal plane has almost constant velocity, and if friction were entirely absent
-Galileo also stated that the tendency of a moving body to keep moving is
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-the ball would move forever
-natural and that every object resists change to its state of motion
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Inertia
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the property of a body to resist changes to its state of motion
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Newton's First Law
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every object continues in a state of rest, or of uniform speed in a straight line, unless acted on by a nonzero net force
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Isaac Newton's laws of motion
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replaced the Aristotelian ideas that had dominated thinking for about 2000 years
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Another name for Newton's First Law
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Law of Inertia
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Forces are needed to
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overcome any friction that may be present. Forces are also needed to set objects in motion initially
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Once an object is moving in a force-free environment, it will
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move in a straight line indefinitely
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The more mass an object has, the greater
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its inertia and the more force it take to change its state of motion
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Mass
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-the quantity of matter in an object
-measure of the inertia of an object
-measure in the fundamental unit of kilograms
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Weight
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-the force of gravity on an object
-depends on an object's location
-same whether the object is located on earth, the moon, or in outer space
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Mass and Weight are proportional to each other in a given place.
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Objects with great mass have great weight; objects with little mass have little weight
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In most parts of the world, the measure of matter is commonly expressed in units of
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mass. The SI unit of mass is the kilogram and its symbol is kg.
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The SI unit of force is the
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newton
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The SI unit for the newton is
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N and is written with a capital letter because it is named after a person
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The Law of Inertia states that
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objects in motion remain if no unbalanced forces act on them
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Copernicus announced the idea of a moving Earth in the 16th century..
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this controversial idea stimulated much argument and debate
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Newton's work showed that objects on Earth move
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with Earth as Earth moves around the sun. The Law of Inertia also shows that objects within moving vehicles move with the vehicles
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Notions of motion today are very different from
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those of our distant ancestors.
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An object is moving if
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its position relative to a fixed point in changing
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When we describe the motion of one object with respect to another,
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we say that the object is moving relative to the other object
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Unless stated otherwise, when we discuss the speeds of things in our environment
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we mean speed with respect to the surface of Earth
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You can calculate the speed of an object by
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dividing the distance covered by time
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Galileo is credited as being the first to measure speed
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by considering the distance covered and the time it takes
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Speed
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how fast an object is moving
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Any combination of units for distance and time that are useful and convenient are
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legitimate for describing speed
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Some units that describe speed are: The slash is read as :
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-mph and kph
-per
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Average Speed
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total distance covered divided by the time
-does not indicate variations in the speed that may take place during the trip
total distance= average speed*travel time
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Speed is a description of how fast an object moves;
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velocity is how fast and in what direction it moves
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Velocity
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speed in a given direction
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A quantity such as velocity, which specifies direction as well as magnitude, is called
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vector quantity
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Scalar Quantity
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quantities that require only magnitude for a description
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Constant Speed
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means steady speed
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Constant Velocity
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means both constant speed and constant direction, which is in a straight line
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If either an objects speed or its direction is changing
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then the objects velocity is changing
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