Instantaneous velocity
For a very short time of travel
vx = slope of graph of x Vs t
If vx = constant, vx = vav,x so for constant vx,
x = vx t
vx > 0, x increasing, motion along +x. vx < 0?
vx x
Consider a graph of vx Vs t
for changing vx
If we break the
Estimation
Example: estimate surface area of human being
Say human is like a cylinder: 6ft ~ 2m tall, 40in ~ 1m circumference
Slit cylinder, unfold it
Rectangle 1 m wide, 2 m high
area = 2m2 surface area of human
being
What is Physics?
Forces and motion o
Find area
Summary of area & slope
Use slope of graph to find:
vx given x-t graph
ax given vx-t graph
Use area under graph to find
x given vx-t graph
vx given ax-t graph
Constant Acceleration
Intro: what is acceleration?
Consider an object moving along a s
Motion along a line with constant acceleration
Illustrations will assume ax > 0 but formulae good also for ax negative
aav,x = ax so ax = vx/t and
vx = vfx vix = axt
x = area under vx-t = (vfx+vix)t
Constant ax Continued
vfx = vix + axt so x = (vix + axt
Various Acceleration
Intro: what is acceleration?
Consider an object moving along a straight line
Object = thing anything
Choose an x axis (like a ruler) along the line
Axis direction: direction in which x increases
Position of object = value of x
Displa
Position, Displacement, Distance
Example: A bug walks 10 cm to the right along a windowsill then turns
and walks 5 cm to the left and stops
What is bugs displacement from start to finish?
What distance did the bug travel, start to finish?
x axis to right,
Vectors
Important Special Case for ax
Consider ax = constant
Motion along a line with constant acceleration
Illustrations will assume ax > 0 but formulae good also for ax negative
aav,x = ax so ax = vx/t and
vx = vfx vix = axt
x = area under vx-t = (vfx+v
What of the following is always true if we drop something?
A.
Its velocity is always zero, at the start and later
B.
Its acceleration is upwards
C.
It will break
D.
vix = 0
E.
x = zero during the problem
Example 1
A bullet starts from rest and accelerates
What is Physics?
Forces and motion of dead things (rocks, cars, planets,
buildings)
Many similar aspects of living things
Why study Physics?
Most reliable knowledge humans can access
o
Tells you the result beforehand correctly!
Learn about chain of causal
Units
Units: Systme International (SI) used in science and international
industry
Length: meter, m (1 2.54 cm, 1m 39.37)
Mass: kilogram, kg (1000 g or ~2.2 lbm)
Second, s
Others to come
Formulas give SI units out ONLY if you put SI units in.
Conversions n