Physics Test: Pressure, Free Fall, and Falling with Air Resistance
free fall acceleration
(g with → over top) the acceleration of an object when gravity is the only force acting on it. often physics books will call this, "acceleration due to gravity." its average value at the surface of the earth is 9.8 m/s²
P
F/A
g
Fg/m = gm/m = g
a
Fnet/m = F ar - Fg/m
air resistance
a force that opposes the motion of a body through air and that is the result of collisions between the moving body and the molecules that compose air. air resistance transforms kinetic energy (energy of motion) to thermal energy. air resistance depends on the speed of the object through the air (the greater the area, the greater the air)
viscosity
a measure of how resistant a fluid is to flow within itself or to the flow of objects through the fluid. the SI unit is the pascal • second or Pa•s, and the quantity symbol is the Greek lower case letter eta, η.
mass
a measure of the inertia of the object. it also measures the quantity of matter in an object. SI unit - kilogram (kg)
viscosity
a way of describing how thick a fluid is
fluid
anything that flows; in particular, any liquid or gas
galileo's law of falling bodies
in a vacuum, and only in a vacuum, all bodies fall with the same acceleration
drag
in both air and liquid, fluid resistance can also be described as this
terminal velocity
terminal speed in a downward direction. the motion of the falling object is at a constant speed in a straight line, so its acceleration is zero.
pascal
the SI unit of pressure, it is equivalent to newtons per square meter (N/m²). atmospheric pressure at sea level is approximately 100 kPa
pressure
the amount of force applied perpendicular to the surface of an object per unit of surface area
weight
the force of an object due to the downward gravitational pull of the Earth on the object. the direction of the ______ force is always downward toward the center of the earth. SI unit = newton (N)
pressure
the force per unit of surface area, where the force is perpendicular to and toward the surface of the object
fluid resistance
the result of interaction between a moving object and the particles of the fluid through which the object moves. the fluid can be a gas (air) or a liquid (water or oil)
terminal speed
the speed at which the acceleration of a falling object becomes zero because the upward force due to fluid resistance terminal speed is its maximum downward speed
elapsed time
the time that has passed since the beginning of an event, usually measured in seconds (s)
free fall
the vertical (up or down) motion of any object when the force acting on it is gravity, as measured by the weight of the object. "in a vacuum, and only in a vacuum, all objects fall at the same rate."
free fall
the vertical motion of an object when the ONLY vertical force acting on it is gravity. for this to actually occur, the object must be in "vacuum" - an empty region where there is no air or any other gaseous quantity - and therefore, absolutely no air resistance. ______ ____ motion itself can be either the upward or downward direction. if the object is moving upward, it slows; if moving downward, it speeds up. if the vertical motion of an object is such that a physics problem says to "neglect air resistance" or that "air resistance is negligible," the motion can be considered to be in free fall.
weight-to-mass ratio
the weight of an object divided by the mass of the object. this ratio always has the same value at the same location, regardless of the object. at the surface of the earth, the ratio is equal to 9.8 N/kg or 9.8 m/s² for all objects, and is given the symbol "g"
