# Newton's second law of motion

### Newton's second law of motion

#### Lessons

In this lesson, we will learn:
• Newton's second law of motion
• Problem solving with Newton's second law of motion

Notes:

• Newton's second law: If a net force acts on an object, its velocity changes. The acceleration is proportional to the magnitude of the net force, and inversely proportional to the mass, or $\vec{F}_{net}=ma$
• The force of gravity acting on an object is $\vec{F}_{g}=mg$, where $g$ is acceleration due to gravity (9.81 m/s2 [down])
Newton's Second Law

$\Sigma \vec{F} = \vec{F}_{net} = m\vec{a}$

$\Sigma \vec{F}:$ sum of all forces, in newtons (N)

$\vec{F}_{net}:$ net force, in newtons (N)

$m:$ mass, in kilograms (kg)

$\vec{a}:$ acceleration, in meters per second squared $(m/s^{2})$

• Introduction
Introduction to Newton's second law
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Meaning of Newton's second law
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Newton's second law formula
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Newton, the unit of force

• 1.
Applying Newton's second law
a)
What is the unbalanced force required to accelerate a 1370 kg car at 4.25 $m/s^{2}$?

b)
What is the unbalanced force required to bring a 995 kg car travelling at 11.5 m/s to a stop in 30.0 m?

c)
An apple falls from a tree.

i. What is the force of gravity acting on a falling 0.200 kg apple?

ii. If the apple is accelerated downwards at 9.53 $m/s^{2}$, find the force of air resistance acting on the apple.