A force is needed to

change an objects state of motion

The combination of all forces acting on an object is called the

net force

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

zero on the rock

The scientific unit of force is the newton--

abbreviated N

Tension is a

stretching force

Weight is the force of gravity

acting downward on an object

A vector is an arrow that

represents the magnitude and direction of a quantity.

A vector quantity is a quantity that needs both magnitude and

direction for a complete description

-an example would be force

-an example would be force

A scalar quantity is a

quantity that can be described by magnitude only and has no direction. -time, area, and volume are scalar quantities

You can express the equilibrium rule mathematically as

(funky backwards E letter)F=0

-e letter stands for the sum of

-f stands for forces

-e letter stands for the sum of

-f stands for forces

Mechanical Equilibrium is a

state wherein no physical changes occur; it is a state of steadiness

Whenever the net force on an object is zero, the object is said to be in

mechanical equilibrium

What is the Equilibrium Rule?

Whenever the net force on an object is zero, the object is said to be in mechanical equilibrium

For a suspended object at rest, the forces acting upward on the object must be

balanced by other forces acting downward to make the vector sum equal zero

For an object at rest on a horizontal surface,

the support force must equal the objects weight

A support force is the upward force

that balances the weight of an object on a surface. A support force is often called the normal force

An upward support force is

positive and a downward weight is negative

-The weight of a book sitting on a table is a negative force

-The atoms squeeze

-The compressed atoms produce

-The atoms squeeze

-The compressed atoms produce

-that squeezes downward on the atoms of the table

-upward on the book.

-the positive support force.

-upward on the book.

-the positive support force.

Objects at rest are said to be in

static equilibrium

Objects moving at constant speed in a straight line path are said to be in

dynamic equilibrium

Equilibrium is a state of

no change

An object under the influence of only one force

cannot be in equilibrium

Only when there is no force at all, or when two or more forces combine to zero, can

an object be in equilibrium

Both static equilibrium and dynamic equilibrium are examples of

mechanical equilibrium

The Parallelogram Rule

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

Resultant

the sum of two or more vectors

Combining vectors is simple when they are parallel.

-If they are in the same direction

-If they are in opposite directions

-If they are in the same direction

-If they are in opposite directions

-they add

-they subtract

-they subtract

To find the resultant of nonparallel vectors

use the parallelogram rule

When applying the parallelogram rule to two perpendicular vectors that are equal in magnitude

-the parallelogram is a square.

The resultant is root 2, or 1.414, times one of the vectors

The resultant is root 2, or 1.414, times one of the vectors

When an object is suspended at rest from two non-vertical ropes, there are three forces acting on it:

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.

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.

Aristotle

the foremost Greek scientist

-studied motion and divided it into two types

--natural motion

--violent motion

-studied motion and divided it into two types

--natural motion

--violent motion

During Aristotle's time, natural motion on Earth was thought to be

either straight or straight down: It was 'natural' for heavy things fall and fog very light things to rise

Violent Motion

was imposed motion and it was the result of forces that pushed or pulled

The proper state of objects was thought to be one in rest, unless they were being

pushed or pulled or were moving towards their natural resting place

Copernicus reasoned that the simplest way to interpret astronomical observations was to assume

that Earth and the other planets move around the sun

Copernicus' idea of motion in space was extremely controversial at the time, because most people believed that

Earth and the other planets move around the sun.

Copernicus worked on his ideas in secret to escape

persecution. At the urging of his close friends, he published his ideas

Galileo argued that only when friction is present

as it usually is, is a force needed to keep an object moving

One of Galileo's greatest contributions to physics was

demolishing the notion that a force is necessary to keep an object moving. A force is any push or pull.

Friction

the force that acts between materials that touch as they move past each other

-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

-Galileo also stated that the tendency of a moving body to keep moving is

-the ball would move forever

-natural and that every object resists change to its state of motion

-natural and that every object resists change to its state of motion

Inertia

the property of a body to resist changes to its state of motion

Newton's First Law

every object continues in a state of rest, or of uniform speed in a straight line, unless acted on by a nonzero net force

Isaac Newton's laws of motion

replaced the Aristotelian ideas that had dominated thinking for about 2000 years

Another name for Newton's First Law

Law of Inertia

Forces are needed to

overcome any friction that may be present. Forces are also needed to set objects in motion initially

Once an object is moving in a force-free environment, it will

move in a straight line indefinitely

The more mass an object has, the greater

its inertia and the more force it take to change its state of motion

Mass

-the quantity of matter in an object

-measure of the inertia of an object

-measure in the fundamental unit of kilograms

-measure of the inertia of an object

-measure in the fundamental unit of kilograms

Weight

-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

-depends on an object's location

-same whether the object is located on earth, the moon, or in outer space

Mass and Weight are proportional to each other in a given place.

Objects with great mass have great weight; objects with little mass have little weight

In most parts of the world, the measure of matter is commonly expressed in units of

mass. The SI unit of mass is the kilogram and its symbol is kg.

The SI unit of force is the

newton

The SI unit for the newton is

N and is written with a capital letter because it is named after a person

The Law of Inertia states that

objects in motion remain if no unbalanced forces act on them

Copernicus announced the idea of a moving Earth in the 16th century..

this controversial idea stimulated much argument and debate

Newton's work showed that objects on Earth move

with Earth as Earth moves around the sun. The Law of Inertia also shows that objects within moving vehicles move with the vehicles

Notions of motion today are very different from

those of our distant ancestors.

An object is moving if

its position relative to a fixed point in changing

When we describe the motion of one object with respect to another,

we say that the object is moving relative to the other object

Unless stated otherwise, when we discuss the speeds of things in our environment

we mean speed with respect to the surface of Earth

You can calculate the speed of an object by

dividing the distance covered by time

Galileo is credited as being the first to measure speed

by considering the distance covered and the time it takes

Speed

how fast an object is moving

Any combination of units for distance and time that are useful and convenient are

legitimate for describing speed

Some units that describe speed are: The slash is read as :

-mph and kph

-per

-per

Average Speed

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

-does not indicate variations in the speed that may take place during the trip

total distance= average speed*travel time

Speed is a description of how fast an object moves;

velocity is how fast and in what direction it moves

Velocity

speed in a given direction

A quantity such as velocity, which specifies direction as well as magnitude, is called

vector quantity

Scalar Quantity

quantities that require only magnitude for a description

Constant Speed

means steady speed

Constant Velocity

means both constant speed and constant direction, which is in a straight line

If either an objects speed or its direction is changing

then the objects velocity is changing