Please
Do Not Use This Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
Title: Friction Experiment
1.
Aim: To determine the co-efficient of
friction between mild steel plane and the various materials of the slider
trays.
2.
To determine the angle of friction between
these surfaces.
Apparatus:
Please
Do Not Use This Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
THEORY:
*GENERAL KNOWLEDGE*
Theory 1:
Static Friction
The
coefficient of static friction μs can be measured experimentally for an object
placed on a flat surface and pulled using a known force. The coefficient of
static friction is related to the Normal Force FN of the object on the surface, when the object just begins to
slide. Using what we have
covered
in class, you can derive this
relationship yourself!
Hint
#1: The normal force FN and the weight mg (gravitational
force) are equal. Why?
Hint
#2: The force of friction FF is equivalent to the normal force FN times the coefficient of
friction
μ.
Kinetic Friction
You
can calculate the coefficient of kinetic friction, μk using
a variation of the method you used for the coefficient of static friction. For
the coefficient of kinetic friction, you can use the same free body diagram as
the one drawn on the first page. Now, the combination of the force of tension
and the force of friction will need to add up such that the block will slide at
a constant speed or with zero acceleration. Think of Newton’s first and second
laws when you set up this equation.
Theory 2:
Static and Dynamic Friction
Goals: Our
purpose in this laboratory is to investigate the laws that govern friction.
Theory: We
encounter friction at almost all times during the day. Friction between our
foot and
the
floor helps us walk. In spite of its importance, friction is still not well
understood. However,
empirical
laws describe the friction between two surfaces. These laws are as follows:
1.
The ratio of the maximum frictional force and the normal force is a constant
and equals the
coefficient
of friction, , and
depends only on the nature of the two surfaces in contact. I.e.:
(Frictional Force) / (Normal Force).
2.
The coefficient of friction is independent of the area of contact.
3.
The coefficient of kinetic friction k (the object is in motion) is lower than the coefficient
of
static
friction s(the
object is stationary.)
We
will first use the configuration shown in Fig. 1 to determine the coefficient
of static and
kinetic
friction between a few surfaces. Here, the normal force N = Mg, obtained by
balancing
forces
in the vertical direction on the block. Recall that the pulley only changes the
direction of
force
but does not change its magnitude. Balancing forces in the horizontal
direction, we obtain:
mg
- N = 0.
Therefore,
= m/M.
Next,
we explore if there is a substantial change in if the surface on which the block is sliding
is
at an angle to the horizontal. In this case the normal force N is not equal to
Mg, but rather to
Mg
cos. Balancing forces along
the inclined plane when the block is about to move up the
plane,
we obtain:
mg - N - Mg sin= 0 .
Substituting
for N, we obtain:
= (m/M - sin)/cos .
(Note:
When the block is about to move downwards, the direction of the frictional
force is in
opposite
direction and therefore you will have to modify the formula appropriately.)
For Procedures, See your Mechanical Laboratory Manual.
Please
Do Not Use This Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
Observations :-
1.
Comparison between Cam & Follower
2.
Type of Motion to be named
Applications:-
1. Cams are used in
Automatic machines
2. In internal
combustion engine
3. In machine tools
4. Printing Control mechanisms
PRECAUTIONS:
For
Precautions, See General Laboratory Precautions
Please
Do Not Use This Reference Material WORD FOR WORD View Terms Of usage policy Page of this site for more Info on how to use this site
Blogger Comment
Facebook Comment