Transcript Forces and Free Body Diagrams (FBD)

Forces and Free Body
Diagrams (FBD)
Forces
• A force causes an object to change its velocity,
by a change in speed OR direction
• Force is a vector quantity since direction is
important
• There are contact forces between objects that
touch and there are field forces between
objects that do not touch
Forces
• SI Unit for Force is the Newton (N)
• The formula for force is F = ma
NOTE: the unit for
mass is kg and the
unit for acceleration
is m/s2… so a
kg•m/s2 is the same
thing as a Newton!
Type of Force
Symbol
Description
Frictional
Ffrict
force exerted between surfaces
as an object moves across it
Tension
Ftens
force transmitted through a
string, rope, cable, or wire
Normal
Fnorm
force exerted on an object
when it is on top of another
object; ┴ to resting plane
Air Resistance
Fair
force exerted on object as it
travels through the air; usually
negligible
Applied
Fapp
force on an object being
pushed or pulled
Spring
Fspring
force exerted by a stretched or
compressed spring with an
object attached to it
Gravitational
Fgrav
force of gravity that all objects
on Earth experience
Free Body Diagrams (FBD)
FBDs are used to show relative magnitude and
direction of all forces acting on an object in a given
situation, therefore:
1. Draw the object as a box
2. The larger the force the longer the vector
arrow should be
3. The direction of the arrow’s tip should show the
direction that the force is acting
4. Always label your force vectors
5. With constant velocity vectors are equal and
with acceleration/deceleration vectors are unequal
FBD Example
A book on a table is being pushed to the
right at a constant velocity
FBD Example
A parachutist jumps
out of an airplane;
include air resistance
How would I draw the FBD?
How would I draw the FBD?
This is what the FBD
should look like!
How would I draw the FBD?
How would I draw the FBD?
How would I draw the FBD?