Mechanical Engineering
Links and Degrees of Freedom
Grade 10 ST
What is Mechanical Engineering?
• Engineering is a branch of science and
technology that focuses on the analysis and
execution of technological projects such as
building bridges, roads, bicycles, cars and
televisions.
• Mechanical engineering is a branch of
engineering that focuses on the design,
production, analysis, working and
improvement of technical objects
Linking in Technical Objects
• When there are more than two parts in an
object there needs to be a link to hold the two
parts together.
• Any part or fluid that holds together 2 pieces
performs a mechanical function called linking
Characteristics of Links
Every link can have only 4 characteristics
• Direct or Indirect
• Rigid or flexible
• Removable or non-removable
• Complete or partial
Characteristics of Links
Direct
Two parts are held together without a
linking component
Indirect
Two parts are held together by a linking
component
Rigid
When linking component or linked parts
are rigid
Flexible
When linking component or the surfaces
of the linked parts can be deformed
Removable
If linked parts can be separated without
damaging their surfaces or the linking
component
Complete
When the linked parts must move
together
Non- Removable
Separating the linked parts will damage
their surfaces or the linking component
Incomplete
When one part can move independently
of other parts
Practice
The link between the tire
and the wheel is:
• Direct
• Flexible
• Removable
• Complete
Practice
Link between the wheel
and the frame
• Indirect
• Rigid
• Removable
• Partial
Degrees of Freedom of Movement
In a technical object linking limits the possibility
of independent motion of one part in relation
to another.
• Ex: The link between the bicycle tire and the
wheel.
– The tire will always follow the wheel. Therefore,
this is an example of a complete link.
Degrees of Freedom of Movement
Ex: The wheel and frame on a rollerblade.
– The wheel can turn even if the frame is immobile.
Therefore, this is an example of a partial link
Degrees of Freedom of Movement
There are 6 possibilities of independent motion
– 3 translational motions
– 3 rotational motions
A part may have a maximum of six degrees of
freedom.
Degrees of Freedom of Movement
Possibilities
Translation Motion
Rotational Motion
Notation
Translation from left to right or from right to
left
Tx
Translation from top to bottom or from bottom
to top
Ty
Translation from front to back or from back to
front
Tz
Rotation about the x axis
Rx
Rotation about the y axis
Ry
Rotation about the z-axis
Rz
Guiding Controls
Guiding controls force moving parts to follow
specific trajectory
There are 3 types of guiding
– Translational guiding ensures the straight
translational motion of a moving part
– Rotational Guiding ensures the rotational motion
of a moving part
– Helical Guiding ensures both the translational
motion of a moving part while it rotates about the
same axis.
Examples
Examples:
• The window has what kind of guiding?
_____________________________
• The axle on a bike provides what type of
guiding? ____________________
• The peanut butter lid has what type of
guiding?_____________________
Adhesion and Friction
• Adhesion is the phenomenon that enables
two surfaces to remain in contact with each
other without slipping.
• Friction is a force that resists the slipping of
one moving part over another
• Lubrication is the mechanical function
performed by any component that reduces
friction between two parts.
Five Factors that affect the strength of
adhesion between 2 Surfaces
Factor
Nature of the materials in contact
Description
Certain materials adhere to each other
better than others
Presence of a lubricant
Adhesion is usually reduced by the
presence of a lubricant
Temperature
Adhesion between two surfaces tends to
diminish with colder temperatures
State of the surface in contact
Usually, the rougher the surface, the
better its adhesion to another surface
Perpendicular force exerted by one
surface on another
Adhesion increases as the force
increases
How to reduce friction?
• Apply a lubricant
• Polish the surface of the parts
Practice
For each of the following situations, determine whether the strength of adhesion between the surfaces
described will increase or decrease, and identify the factor affecting the strength of adhesion.
a) between the soles of a worker’s boots and the shingles on a roof as the temperature rises over the
course of the day
increase

decrease 
Factor involved: _________________________________________
b) between a hockey puck and the ice as the period advances and the ice becomes rougher
increase

decrease 
Factor involved: _________________________________________
c)
between the wheel of a wheelbarrow and the road after the wheelbarrow has been emptied
increase

decrease 
Factor involved: _________________________________________
Practice
d) between a bicycle chain and the derailleur after oil has been applied
increase

decrease

Factor involved:
e) Between a ping pong ball and the racket if the rubber coating is removed to reveal the
wood underneath
increase

decrease

Factor involved:
5. What force resists the slipping of a piece of sandpaper on a wooden surface?