Based on the newest Paul Hewitt conceptual physics textbook, published 2009

### Fact

close agreement by competent observers who make a series of observations of the same phenonmenon

### Laws or Principles

when hypotheses about the relationship among natural quantities are tested over and over again and not contradicted, may become...

### theory

a synthesis of a large body of information that encompasses well-tested and verified hypotheses about certain aspects of the natural world

### vector quantity

quantity that needs both magnitude and direction for a complete description (Ex: force)

### scalar quanity

quantity that can be described by magnitude only and has no direction (Ex: time, area, and volume)

### Equilibrium rule

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

### Newton's first law (law of intertia)

Newton's first law states that every object continues in a state of rest, or of uniform speed in a straight line, unless acted on by a nonzero net force.

### Mass

measure of the amount of material (matter) in an object and depends only on the number of and kind of atoms that compose it

### instantaneous speed

the speed at any instant (tell speed of a car any instant by looking at speedometer)

### projectile

any object that moves through the air or space, acted on only by gravity (and air resistance, if any).

### Inversely

two values change in opposite directions. Mathematically we see that as the denominator increases, the whole quantity decreases by the same factor.

### Newton's Second Law

the acceleration produced by a net force on an object is directly proportional to the marnitue of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object. Acceleration = net force/mass (a=F/m)

### air resistance

friction acting on something moviing through the air, a common form of fluid friction.

### Pascals (Pa.)

pressure is measured in newtons per square meter. Equal to one newton per square newton.

### Terminal speed

speed at which the acceleration of a falling object is zero because friction balances the weight