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If we draw a box around the two trailers they can be considered a closed system or unit. When we look at the forces on this closed system the following forces will apply (we assume drag forces are absent):

  • The force of the car pulling the unit (trailer A and B)
  • The force of friction between the wheels of the trailers and the road (opposite to the direction of motion)
  • The force of the Earth pulling downwards on the system (gravity)
  • The force of the road pushing upwards on the system

These forces are called external forces to the system.

The following forces will not apply:

  • The force of A pulling B
  • The force of B pulling A
  • The force of friction between the wheels of the car and the road (opposite to the direction of motion)

We can also draw a box around trailer A or B, in which case the forces will be different.

If we consider trailer A as a system, the following external forces will apply:

  • The force of the car pulling on A (towards the right)
  • The force of B pulling on A (towards the left)
  • The force of the Earth pulling downwards on the trailer (gravity)
  • The force of the road pushing upwards on the trailer
  • The force of friction between the wheels of A and the road (opposite to the direction of motion)

Force diagrams

If we look at the example above and draw a force diagram of all the forces acting on the two-trailer-unit, the diagram would look like this:

It is important to keep the following in mind when you draw force diagrams:

  • Make your drawing large and clear.
  • You must use arrows and the direction of the arrow will show the direction of the force.
  • The length of the arrow will indicate the size of the force, in other words, the longer arrows in the diagram (F 1 for example) indicates a bigger force than a shorter arrow (F f ). Arrows of the same length indicate forces of equal size (F N and F g ). Use “little lines” like in maths to show this.
  • Draw neat lines using a ruler. The arrows must touch the system or object.
  • All arrows must have labels. Use letters with a key on the side if you do not have enough space on your drawing.
  • The labels must indicate what is applying the force (the force of the car?) on what the force is applied (?on the trailer?) and in which direction (to the right)
  • If the values of the forces are known, these values can be added to the diagram or key.

Draw a labeled force diagram to indicate all the forces acting on trailer A in the example above.

Free body diagrams

In a free-body diagram, the object of interest is drawn as a dot and all the forces acting on it are drawn as arrows pointing away from the dot. A free body diagram for the two-trailer-system will therefore look like this:

Draw a free body diagram of all the forces acting on trailer A in the example above.

Finding the resultant force

The easiest way to determine a resultant force is to draw a free body diagram. Remember from Chapter [link] that we use the length of the arrow to indicate the vector's magnitude and the direction of the arrow to show which direction it acts in.

Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Maths test. OpenStax CNX. Feb 09, 2011 Download for free at http://cnx.org/content/col11236/1.2
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