First Law Of Motion

Key notes :

Definition of the First Law of Motion:

• The First Law of Motion, also known as the Law of Inertia, states:An object remains in its state of rest or uniform motion in a straight line unless acted upon by an external unbalanced force.

Inertia:

• Inertia is the natural tendency of an object to resist changes in its state of motion or rest.
• The greater the mass of an object, the greater its inertia.

Key Components of the Law:

• Rest: If an object is at rest, it will remain at rest unless an external force acts on it.
• Uniform Motion: If an object is moving with constant velocity, it will continue to do so unless an unbalanced force changes its motion.

Balanced and Unbalanced Forces:

• Balanced Forces: Do not change the state of motion; the object remains at rest or in uniform motion.
• Unbalanced Forces: Cause a change in the state of motion (e.g., start moving, stop moving, or change direction).

Examples of the First Law in Daily Life:

• A book lying on a table remains at rest until pushed.
• A moving car continues to move unless brakes are applied (external force).
• Passengers in a moving bus lurch forward when the bus suddenly stops because their bodies tend to maintain their state of motion.

Significance of the First Law:

• Explains why seat belts are necessary in vehicles (to counteract inertia in case of sudden stops).
• Forms the foundation for understanding motion and force relationships in physics.

Applications:

• Rocket propulsion: A rocket remains stationary until an unbalanced force (thrust) propels it.
• Sports: A football at rest moves when kicked (external force applied).

Experiment to Understand the Law:

• Place a card on a glass and balance a coin on top of the card.
• Flick the card horizontally. The coin falls into the glass due to inertia, demonstrating that it resists the horizontal motion of the card.

Historical Background:

• Proposed by Sir Isaac Newton in his work Philosophiæ Naturalis Principia Mathematica (1687).

Let’s practice!