The force of kinetic friction as function of θ increase, decreases or remains the same.
Justify your observation. ____________________________________________________
________________________________________________________________________
3.
(2 points)
Compared with the maximum value of the force of static friction you calculated in part 1
the force of kinetic friction is larger, smaller or the same? Explain your observation.
________________________________________________________________________
_______________________________________________________________________
Pre-lab Question:
1.
Consider a block sliding down an inclined plane at an angle θ with the horizontal.
If the plane is inclined such that the block is just about to slide down, complete the F.B.D to
show all the component of forces along the x and y direction.
Apply Newton’s 2
nd
law along the x and y
direction and show that
at the threshold of motion
tan θ = µ
s.
(5 Points)
At equilibrium,
ΣF
x
= 0
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motion
Motion

4
At equilibrium,
ΣF
y
= 0
(5 points)
Complete the algebra to prove that
tan θ = µ
s
.
Note: By measuring the tan , the coefficient of static friction, when the objet just begins to
slide can be determined.
2.
(5 Points)
(Phy235) If the angle of the incline is such that the object slides down with a constant
acceleration
a
,
a)
Draw the F.B.D to show all the component of forces along the x and y direction.
b)
Apply Newton’s 2
nd
law along the x and y direction.
At equilibrium,
Σ F
x
= ma
x
At equilibrium,
ΣF
y
= 0
(5 Points)
Complete the algebra to prove that
µ
k
as function of
θ
and the
acceleration
a
is given by
µ
k
=
[g sin (θ) – a ]
For suggestions or changes contact [email protected]

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