Newton's Three Laws of Motion
Definition
Newton's three laws of motion describe the relationship between the motion of an object and the forces acting on it. They form the foundation of classical mechanics.
The Laws
- First Law (Law of Inertia):
- Second Law (Law of Acceleration):
- Third Law (Action-Reaction Law):
An object at rest remains at rest, and an object in motion remains in motion at constant velocity, unless acted upon by a net external force.
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass:
$$
\vec{F}_{\text{net}} = m\vec{a}
$$
where $\vec{F}_{\text{net}}$ is the net force, $m$ is mass, and $\vec{a}$ is acceleration.
For every action, there is an equal and opposite reaction. If object A exerts a force $\vec{F}$ on object B, then object B exerts a force $-\vec{F}$ on object A.
Worked Example
Problem:
A $2,text{kg}$ object is acted upon by a net force of $10,text{N}$. What is its acceleration?
**Step 1:**
Write Newton's second law:
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**Step 2:**
Plug in the values:
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**Step 3:**
Solve for $a$:
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## Takeaways
- Newton's laws explain how forces affect motion.
- The second law provides a quantitative relationship: $F = ma$.
- Every force has an equal and opposite reaction force.