Terminal Velocity - ASU

Terminal

• The object’s velocity
when the acceleration of
falling become ______.

• Air resistance
(Aerodynamic drag)

f(drag coefficient, surface
area, square of velocity,
air density)

Velocity

kV2

BW

ΣF = (kV2-BW) = 0
V=?

Linear K

KIN335 Sp

Kinetics I

pring 2005

What you ha

• Kinetics?
• Force? External or Intern
• Mass, Inertia, Accelerati
• Revisit Newton’s laws o
• Free-body diagram? (Gr
• Friction forces (static an
• Pressure
• Static equilibrium proble
• Dynamics equilibrium p
• Impulse-Momentum Rel

ave to know

nal forces
ion
of motion
raphic, Very Crucial!!)
nd dynamic friction)

ems
problems
lationship

-mechanics

Rigid-body

Statics

system in a
constant

state of motion

Positioin, Kinematic
Velocity,
Acceleration Description of M
(w/o consideri
forces)

Linear A

s Overview

y Mechanics

Dynamics

system
undergoes
acceleration

cs Kinetics

Motion Cause &
ing Results due to

forces

Angular Linear Angular

Force Torque

Kine

• Causes and Effects due t
Î Newton’s

CAUSES
Linear Kinetics Net Forces*

Angular Kinetics __________

* Resultant force derived from the composit

etics

to forces
s 2nd law ___________

Î EFFECTS

__________ movement
(Mass ×Acceleration)

Rotating movement
(Moment of Inertia ×
Angular Acceleration)

tion of two or more forces

Force =

Force r Fixed

* Torque = r·F =

Force =

m·a

= m·a

d center

=

_____

=

a I·α

+

For

• Enable an object to start
change directions.

• Combination of two or m
maintain our balance in s

• Force is a push or a pull
• Mechanical definition: S

when it starts, stops, spe
changes direction.
• YK’s definition: Someth
movement.

rce?

moving, stop moving, and

more forces enables us to
stationary positions.
(simple definition).
Something accelerates
eeds up, slow down, or

hing causes an object’s

For

• Unit : Newton (N)
1.0 N = (1.0 kg)·(1.0 m/s2
1 lb = __________ N

cf) body weight = force = m
• Force is Vector Î Magn
• Classifying forces

– Internal forces
– _________ forces

rce?

2)
m·g
nitude and direction

Internal

• Forces that act within the objec
system whose motion is being
investigated.

• Example:
– ___________________ wit
the whole system
– Muscle contraction

• Important in the study of sport
biomechanics related with the
nature and causes of ________

• Incapable of producing changin
in the motion of the body’s cen
of mass.

l forces

ct or

thin

_.
ng
nter

Externa

• Forces that act on an obj
interaction with the envi

• Classifying external forc

– ____________ force(s) :
and magnetic force

– _______ forces : air resis
ground reaction force(GR
friction, …

al forces

ject as a result of its
ironment surrounding it.

ces

gravitational force, electrical

stance, water resistance,
RF), normal (contact) force,

Notat

• ____: Normal (reaction)
force

• GRF : Ground reaction
force

• ___ : Static friction force
• Fd : Dynamic friction

force
• W : Body weight or

gravitational force
• F : Applied external

force

tions

W

W RN or GRF

RN F
Fs
F
Fd

Ma

• Quantity of matter co
• Direct measure of a b

change in ______ mo
inertia w.r.t linear mo
• The measure of _____
• Inertia? Tendency of
change in its state of m
Î Newton’s 1st law

ass

omposing a body
body’s _________ to
otion (i.e., an object’s
otion)
____
a body to resist a
motion

Newton

• Newton’s 1st law

– Every body continues in its sta
a straight line, unless it is com
forces impressed upon it.

– Special case of Newton’s 2nd l

In case of ΣF = 0, the state of mo
will not change

• Newton’s 3rd law

– Action-Reaction Principle
– Describes how objects interact

n’s laws

ate of rest, or of uniform motion in
mpelled to change that state by
law

otion (constant velocity or zero velocity)

t with one another

Accele

eration

Free-Body Di

• Sketch that shows a defined
of the force vectors acting on

• a pictoral representation of N
indicating all acting _______

iagram (FBD)

system in _________ with all
n the system

Newton's second law Î
_ and _______ due to forces

Free-Body Di

• Four Steps to do

1. Determine the body to be isolate

2. Isolate the body with a diagram
represents the complete external
boundaries.

3. Represent all ________ forces th
on the isolated body in their prop
positions within the diagram.
(Gravitational force, GRF, Nor
force, Friction force, Push or P
resistance….)

4. Indicate the choice of ________
directly on the diagram.

iagram (FBD)

ed.
that
l

hat act
per

rmal
Pull, Air

___ axes

Example)



Bat? Body?

Whole body + Bat





Friction Revie

• Understand friction fo
that contribute to frict

– Coefficient of friction
– Normal reaction force
– Surface area (?)

• Know how to calcula
coefficients of static a
kinetic) friction.

ew Objectives

orce and the factors
tion force.

n
e

ate friction forces and
and dynamic (or

Friction

• Surface _________ due to no
force acting on the surface.

• Vector (magnitude and direc
• Direction : _______ to the su

& __________ to movement
opposite to tendency of mov
• Magnitude : F = µ⋅ RN

– Static friction :Fs = µs⋅ RN
– Dynamics (Kinetic) friction :

Fd = µd⋅ RN

µ : friction coefficient
(_________________

RN :Normal force
(___________________

n Force FW

ormal

ction)
urface
t or
vement

W
_)
_)

Draw the direct

tion of friction?

Magnitude of F
F=µ

• Proportional to the
normal contact force
(RN) Î ↑ W, ↑____
↓W, ↓ RN

• Inversely proportional
to the angle of
inclination
Î↑ θ, ↓ _____
↓ θ, ↑ RN

Friction Force
µ⋅ RN

θ θ Wn
W Wt
Figure 1a

Magnitude of F
F=µ

• Proportional to the friction c
Î ↑ µ, ↑ F
↓ µ, ↓ F

• µ = f (material, surface cond
Îdepend on characteristics bet
ÎMetal, rubber, wood,….
ÎSand, oil, water, dry,….

• _______ Friction vs. ______
Coefficients

Friction Force
µ⋅ RN

coefficient (µ)

dition)
tween an object and surface.

___ (Kinetic) Friction

Static vs. Dyna

• Static friction (before moving) :
Proportion to ___________ but
opposite direction.

• Max static friction (about to
move) : Max resisting force to
prevent movement (Flim)

• Dynamic friction : ________
resisting force to prevent
movement

• Static friction coefficient (µs)
µs = Flim /RN

• Dynamic (kinetic) friction
coefficient (µd)
µd = F /RN

Always
___________

amics Friction

Force applied