Motion in One Dimension Chapter Two Lets Ponder

Motion in One Dimension Chapter Two

Let’s Ponder! n What means of motion has done more to change the way cities are build than any other? n The elevator

Motion is relative! n If you are traveling on a plane, you are not moving relative to the plane – you are moving relative to the Earth.

Motion is Relative! n n In physics, a frame of reference is chosen against which changes in position are measured. Commonly, the Earth is used as a frame of reference in physics problems, and motion is measured relative to Earth.

Distance vs. Displacement Distance and displacement are not the same thing! n Distance: the total amount of space a moving object has covered. n

Distance vs. Displacement n Displacement: the length of a straight line drawn from an object’s initial to final position

Distance vs. Displacement n Is a change in position: Δx = xf – xi n n (sometimes also shown Δx = x 2 – x 1) Is not always equal to the distance traveled n Can be positive or negative n

Velocity Is not the same as speed – velocity includes direction as well as magnitude. n Example: n 100 km/hr is speed (notice magnitude only) n 100 km/hr North is velocity n

Velocity Can be interpreted graphically! n On a graph of position (y axis) vs. time (x axis) n Velocity is the slope of the graph n

Average Velocity Average velocity can be expressed by the following equation: n V(ave) = Δx/Δt n Where: x = position and t = time. n However – average velocity can also be shown using “d” for position (distance) n Many time the “(ave)” and “Δ” are not shown, but assumed in equations n

Instantaneous Velocity at a given time (t) n Can solve mathematically n Can solve graphically (slope tangent to the curve of the graph) n

Velocity n Always lots of fun! n What if velocity changes?

Acceleration Rate of change of velocity with respect to time n Can be a change in speed or direction! n Has both direction and magnitude (a number value) n Equation: aave = Δv/Δt n

Acceleration n Can be described by the slope and shape of a graph!

Acceleration n If an object is dropped or thrown and only gravity acts on the object after release, the object is said to be in a state of free-fall.

During Free-Fall Acceleration is constant n The name we give it is “gravity” n The magnitude of gravity is given as 9. 81 m/s 2 n

During Free-Fall Acceleration is constant during both upward and downward motion n Acceleration is always directed downward during free fall n