# Free Body Diagrams

Urban and Civil

Nov 29, 2013 (4 years and 7 months ago)

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Free Body Diagrams

Push or pull

The cause of an acceleration or the change in an
object’s velocity (pg. 124)

Contact force
-

force that arises from the
physical contact of two objects

Ex: pulling a spring, pull a wagon, pushing car

Field force
-

force that can exist between objects,
even in the absence of physical contact between
the objects

Ex: gravity, electrical charges

Force which is applied to an object by a person
or another object

F
app
: student pushing or pulling a desk across the
room

Force with which the earth, moon, or other
massively large object attracts another object
towards itself.
(By definition, this is the weight
of the object)

F
grav
: = mass x acceleration due to gravity

Where acceleration due to
gravity is 9.8 m/s
2

The support force exerted upon an object
which is in contact with another stable object.

Ex: book resting on a table, the table is exerting an
upward force upon the book in order to support the
weight of the book

F
norm

The force exerted by a surface as an object
moves across it or makes an effort to move
across it
F
frict

=
(“mu”) (
f
norm
)

Sliding and static friction

Force which acts upon objects as they travel
through air
(often observed to oppose the motion of an
object)

F
air
: skydiver, or downhill skier

Force which is transmitted through a string,
rope, cable or wire when it is pulled tight by
forces acting from opposite ends.

F
tens:

Force exerted by a compressed or stretched
spring upon any object which is attached to it.

F
spring:

The 'coefficient of friction' (COF), symbolized
by the Greek letter µ “mu”, is a
dimensionless

scalar

value which describes the ratio of the
force of friction between two bodies and the
force pressing them together.
The coefficient of friction
depends on the materials used; for example, ice on steel has a low coefficient of
friction, while rubber on pavement has a high coefficient of friction. Coefficients of
friction range from near zero to greater than one

under good conditions, a tire on
concrete may have a coefficient of friction of 1.7

“mu” =coefficient of friction

A book is at rest on a table top.
Draw the free
body diagram that depicts this action.

An egg is free
-
falling from a nest in a tree.
Neglect air resistance. Draw a free
-
body
diagram showing the forces involved

A flying squirrel is gliding (no wing flaps) from
a tree to the ground at constant velocity.
Consider air resistance. A free body diagram
for this situation looks like…

A rightward force is applied to a book in order
to move it across a desk. Consider frictional
forces. Neglect air resistance. Construct a free
-
body diagram. Let’s see what this one looks
like.