NEWTON’S SECOND LAW
Purpose:
To verify Newton's laws when applied to an aircar that is allowed to slide down a frictionless inclined
plane.
Apparatus:
Air track, Motion Sensors and Computer,
Air blower, Glider, Wood blocks, Card attachment for
glider, Balance, Force sensor, Mass, micrometer and string(Make sure aircars are clean on the
underside!! Also clean the airtracks when air is blowing.)
Background:
We would like to verify Newton's second law
Σ
F
= m
a
E
q
.
1
)
and determine if the law is valid.
Because the law is so general no one experiment can prove the law
conclusively.
We will apply Newton's laws to a situation and then verify the theoretical results by
experimentation.
Let us examine the situation of a block of mass M sliding down a frictionless inclined plane.
From practical experience we know that the block will slide down the plane.
By applying Newton's second
law we can determine the rate of acceleration.
Θ
Figure 1.
Illustration of the two forces, the normal force N, and the weight mg,
that cause the block to slide down the
inclined plane.
From figure 1,
Mg, the weight of the block, and N, the normal force, are the only two forces acting on the
block.
Applying Newton's second law yields
Σ
F
=
N
+m
g
= m
a
E
q
.
2
)
This is broken down into x and y components
10
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View Full DocumentΣ
F
x
= mgSin(
Θ
) = ma
Eq.3)
Σ
F
y
= N  mgCos(
Θ
)
=
0
E
q
.
4
)
The object cannot accelerate in the y direction so the forces along that direction must be in equilibrium and
equation 4 results. Along the x axis the forces are not in equilibrium and the block accelerates down the
plane.
From equation 3 the net acceleration of the block is equal to
a = gSin(
Θ
) = constant.
Eq. 5)
Here we see that the acceleration is strictly due to gravity and the angle of the incline.
In this
situation the mass of the object does not affect the acceleration of the block.
This fact is not true in all
situations. For forces not due to gravity, like a force from a spring, we should not forget the role that the
mass of the object plays.
In this experiment we will try to verify that equation 5 describes the acceleration of a block sliding
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 Fall '09
 JohnJames
 Acceleration, Force, Friction

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