**Chapter 1**

**Models**: a
replica or description designed to show structure or workings of an object,
system, or concept

**System**:a set
of items or interactions considered a distinct physical entity for the purpose
of study

**Controlled experiment**: experiment involving manipulation of a single variable or factor

**Accurancy**:
the extent to which a reported measurement approaches the true value of the
quantity measured

**Precision**:
the degree of exactness or refinement of a measurement

**Significant figures**: those digits in a measurement that are known with certainly plus
the first digit that is uncertain

- Physics is the study of the physical world, from motion and energy to light and electrity

- Physics uses the scientific lthoed to discover general laws that can be used to make predictions abouta variety of situations

- A common technique in physics for analyzing a complex situation is to disregard irrelevant factors and create a model that describes the essence of system or situation.

- Physics measurements are typically made and expressed in SI, a system that uses a set of base units and prefixes to describe measurements of physical quantities

- Accurancy describes how close a measurement is to reality. Precision describes the limitations of measuring device used.

- Significant figures are used to indicate wich digits in a measurement are actual measurments and which are estimates.

- Significant-figure rule provides a means to ensure that caculations do not report results that are more precise that the data used to make them.

- Physicists make their work easier by summarizing data in tables and graphs and by abbreviating quantities in equations

- Dimensional analysis can help indentify whether a physics expression is a valid one.

- Order-of-magnitude calculations provide a quick way to evaluate the appropriatrness of an answer.

**Velocity**:
the quantity that measures how fast something moves from one point to another

**Displaceement**:the change in position of an object

**Average velocity**: total displacement divided by the time interval during which the
displacement ocurred

**Acceleration**:
the rate of change of velocity

**Average Acceleration**: (change in velocity)/(change in time)

**Free fall**:
motion of an object falling with a constant acceleration

- Displacement is a change of position in a certain direction, no the total distance traveled.

- The average velocity of an object during some time interval is eaul to the displacement of the object divided by the time interval. Like displacement velocity indicates both size and direction

- The average velocity of an object is given by the following equation: displacement / time

- The average velocity is qual to the slope of the straight line connecting the initial and final points on a graph of the position of the object versus time.

- The average acceleration of an object during a certain time interval is equal to the change in the objects velocituy divided bu the time interval. Acceleration has both magnitude and direction.

- The direction of the acceleration is not always the same as the direction of the velocity. The direction of the acceleration depends on the direction of the motio and on whether the velocity is increasing or decreasing.

- The average acceleration of an object is given by the following equation: change in velocity / time

- The average acceleration is eaul to the slope of the straight line connecting the initial and final points on the graph of the velocity of the object versus time.

- An object thrown or dropped in the rpesence of Earth’s gravity experiences a constant acceleration deirected toward the center of Earth. This acceleration is called the free-fall acceleration, or the accelearion due to gravity.

- Free-fall acceleration is the same for all objects, regardless of mass.

- The value for free-fall acceleration: -9.81 m/s^2

- The direction of the freefall acceleration is considered to be negative because the object accelerates toward Earth.

**Scalar**: a physical quantity that has only a magnitude but no direction

**Vector**: a physical quantity that has both a megnitude and a direction

**Resultant**: a vector representing the sum of two or more vectors

**Components of
a vector**: the projections of a vector along the
axes of a coordinate system

**Projectile
motion**: motion of objects moving in two dimensions
under the influence of gravity

**Frame of reference**: a coordinate system for specifying the precise location of objects
in space

- A scalar quantity completely specified by only a number with appropiate units, whereas a vector is a quantity that has magnitude and direction

- Vectors can be added graphically using the triangle method of addition, in which the tail of one vector is placed at the head of the other. The resultant is the vector drawn from the tail of the first vector to the head of the last vector.

- The Pythagorean theorem and the tangent function can be used to find the magnitude and direction of the resultant vector.

- Any vector can be reolved into it’s component vectors using the sine and the cosine functions.

- Negelcting air resistance, a projectile has a constant horizontal velocity and a contant downward free-fall acceleration.

- In the absence of air resistance, projectile follow a parabolic path.

- If the frame of reference is denoted with subscripts, the the velocity of an object with respect to a different frame of reference can be found by adding the known velocities so tha the subscript starts with the letter that ends the preceding velocity subscript, Vab = Vac + Vcb .

- If the order of the sibscripts is reversed, there is a change in sign, for example: Vcd = -Vdc

**Force**: the
cause of an acceleration, or the change in an object’s velocity

**Contact force**: forced that arises from the physical contact of two objects

**Field force**:
force that can exist between objects, even in the absence of physical contact
between the objects

**Force diagram**: a diagram of the objects involved in a situation and the forces
exerted on the objects

**Newton’s First Law**: an object at rest remains at rest, and an object in motion
continues in motion with contnt velocity (that is, constant speed in a straight
line) unless the object expriences a net external force.

**Inertia**: the
tendecy of an object to maintain it state of motio

**Net external force**: the total force resulting from a combination of external forces on
an object; something called the resultant
force

**Equilibrium**:
the state in which there is no change in a body’s motion

**Newton’s Second Law**: The acceleration of an object is directly proportional to the net
external force acting on the object and inversely proportional to the object’s
mass.

**Newton’s Third Law**: If two objects interact, the magnitude of the force exerted on
object 1 by object 2 is equal to the magnitude of the force simultaneously
exerted on object 2 by object 1, and these two forces are opposite in
direction.

**Weight**: the
magnitude of the force of gravity acting on an object

**Normal force**:
a force exerted by one object on another in a direction perpendicular to the
surface of contact

**Static friction**: the resistive force that opposes the relative motion of two
contacting surfaces that are at rest with respect to one another.

**Kinetic friction**: the resistive force that opposes the relative motion of two
contacting surfaces that are moving past one another

**Coefficient of friction**: the ratio of the force of friction to the normal force acting
between two objects Uk=Fk/Fn Us=Fs/Fn

- Force is a vector quantity that casues changes in motion

- Force can act either through the physical contact of two objects or at a distance

- A free-body diagram shows only the forces that act on one object. These are the only forces that affect the motion of that object.

- The tendency of an object to maintain it state of motion is called inertia. Mass is the physical quantity used to measure inertia.

- The net external force acting on an object is the vector sum of all the forces acting on it. An object is in a state of equilibrium when the net external force on it is zero.

- The net external force acting on an object is equal to the product of the mas of the object and its acceleration.

- When two bodies exert force on each other, the forces are equal in magnitude and opposite in direction. These forces are called action-reaction pairs. Forces always exist in pairs.

- The weight of an object is equal to the mass of the object times the acceleration due to gravity.

- A normal force is a contect force exerted by one surface on another opposite to the direction of the motio of the surfaces. The force of friction between two surfaces is proportional to the normal force.