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Newton’s
Laws of
Motion
CH6
Physics (A)
Fall, 2010-2011
Newton’s
Laws of
Motion
I. Law of Inertia
II. F=ma
III. Action-Reaction
Newton’s 2nd Law
(Eq. 11)
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2nd Law
The net force of an object is
equal to the product of its mass
and acceleration, or F=ma.
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2nd Law
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The unit for force is in newtons (N).
1 N = 1 (kg)∙(m/s2).
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2nd Law (F = m ∙ a)
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How much force is needed to accelerate a 1400
kilogram car 2 meters per second2?
Given:
Unknown:
m=1400 (kg)
F=?
a=2 (m/s2)
Equation: F = ma
Plug-In: F = [1400 (kg) ∙ 2 (m/s2)]
Solve: F =2800 (kg∙m/s2) OR
F= 2800 (N)
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Applying Force - Pressure
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We Say: Pressure is the amount of force
applied per area of something
Ex. 32 psi of tire pressure = 32 lb/in2
We Write: P = F
A
(Eq. 12)
Units for Pressure are N/m2 OR Pa (Pascal)
As Pressure increases, Area decreases
Ex. Barefeet & Rocks
Ex. Snowshoes
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Newton’s 2nd Law proves that different masses
accelerate to the earth at the same rate, but with
different forces.
• We know that objects
with different masses
accelerate to the
ground at the same
rate.
• However, because of
the 2nd Law we know
that they don’t hit the
ground with the same
force.
F = ma
F = ma
98 N = 10 kg x 9.8 m/s/s
9.8 N = 1 kg x 9.8 m/s/s8
F = ma,
Where Did It Come From?
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Let’s Go Launch Stuff!
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