Download Note 2 Force and Motion

Note 2 Force and Motion
This class is all about the relationship between force and motion.
Experiment 1
Drop an object from a height.
Conclusion 1
Force makes objects move. This is also how we define force operationally.
Experiment 2
How does the object moves?
Conclusion 2
Force accelerates objects.
Experiment 3
Place the object on a table.
Conclusion 3
Only the net force accelerates objects.
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Experiment 4
Change the net force on the object without changing the mass of the object.
Here is the cart pulled by a certain weight.
Here is the cart pulled by a twice the weight.
Conclusion 4
The larger the net force, the larger the acceleration. The net force on the object is measured to be
proportional to the acceleration of the object.
ΣF ∝ a or
ΣF
= constant for m constant a
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Experiment 5
Change the mass of the object without changing the net force on the object.
Conclusion 5
The larger the mass, the smaller the acceleration. The mass of the object is measured to be
inversely proportional to the acceleration of the object.
m∝
1
or ma = constant for ΣF constant
a
Experiment 6
Can we find any other parameters that matter?
Conclusion 6
No.
The final conclusion here is that the acceleration of an object is produced by the net force
moderated by the mass of the object.
a=
ΣF
m
This is Newton’s second law of motion. The forces and the net force and the acceleration
are all vectors. It is usually written this way.
!
!
ΣF = ma
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