Newton’s Laws of Motion
1. First Law (Law of Inertia)
● Statement: An object remains at rest or in uniform motion in a straight line unless
acted upon by an external force.
● Explanation:
○ If no net external force acts on an object, its velocity will not change.
○ Objects resist changes to their motion – this property is called inertia.
● Examples:
○ A book on a table stays at rest until pushed.
○ A moving car stops only when brakes (friction) are applied.
2. Second Law (Law of Force and Acceleration)
● Statement: The rate of change of momentum of an object is directly proportional to
the applied force and takes place in the direction of the force.
● Mathematical Form:
F = ma
= Force (N)
= Mass (kg)
= Acceleration (m/s²)
● Explanation:
○ A greater force causes a greater acceleration.
○ Heavier objects require more force to accelerate.
● Examples:
○ Pushing a light object accelerates it faster than a heavy object.
○ A car accelerates more slowly if it carries heavy luggage.
3. Third Law (Action-Reaction Law)
● Statement: For every action, there is an equal and opposite reaction.
● Explanation:
○ Forces always occur in pairs and act on different bodies.
○ The action and reaction forces are equal in magnitude but opposite in
direction.
● Examples:
○ A rocket propels forward by expelling gases backward.
○ When you push against a wall, it pushes back with equal force.
1. First Law (Law of Inertia)
● Statement: An object remains at rest or in uniform motion in a straight line unless
acted upon by an external force.
● Explanation:
○ If no net external force acts on an object, its velocity will not change.
○ Objects resist changes to their motion – this property is called inertia.
● Examples:
○ A book on a table stays at rest until pushed.
○ A moving car stops only when brakes (friction) are applied.
2. Second Law (Law of Force and Acceleration)
● Statement: The rate of change of momentum of an object is directly proportional to
the applied force and takes place in the direction of the force.
● Mathematical Form:
F = ma
= Force (N)
= Mass (kg)
= Acceleration (m/s²)
● Explanation:
○ A greater force causes a greater acceleration.
○ Heavier objects require more force to accelerate.
● Examples:
○ Pushing a light object accelerates it faster than a heavy object.
○ A car accelerates more slowly if it carries heavy luggage.
3. Third Law (Action-Reaction Law)
● Statement: For every action, there is an equal and opposite reaction.
● Explanation:
○ Forces always occur in pairs and act on different bodies.
○ The action and reaction forces are equal in magnitude but opposite in
direction.
● Examples:
○ A rocket propels forward by expelling gases backward.
○ When you push against a wall, it pushes back with equal force.
