Newton’s Laws of Motion - Newton's First Law of Motion

Inertia is the tendency of objects to resist changes in their state of motion. Newton’s First Law of Motion, also called the Law of Inertia, explains this behaviour:
"An object at rest stays at rest, and an object in motion stays in motion, unless acted upon by an external force."

Newton’s First Law of Motion states that

• If no force is acting on a body, its velocity does not change. This means the body will not accelerate unless a force is applied to it.
• If a body is at rest (stationary), it will stay at rest unless a force acts on it.
• If a body is already in motion, it will keep moving in a straight line at the same speed unless a force acts to change its motion (like friction, air resistance, or a push).

Reasons Behind Observations Related to Newton's Laws of Motion:

1. A static object does not move without the application of a force: Objects at rest resist motion due to inertia. A force is required to overcome this resistance and start motion.
2. A force that can lift a book is not enough to lift a table: the table has more mass than the book, so it has greater inertia, requiring a stronger force to move it.
3. Fruits fall from a tree when the branches are shaken: The fruit’s inertia keeps it in its current state (at rest), but when the branch is shaken, the fruit’s attachment is disturbed, and it falls.
4. An electric fan keeps rotating even after switching off: The fan blades have inertia, which keeps them moving in the same state of motion until friction or air resistance gradually slows them down.

Newton’s first law was for scenarios where net force = 0. The second law is for scenarios with a net force not equal to 0. Momentum plays a crucial role in the Second Law.

• Momentum is the product of the mass of a body and its velocity
• It is a Vector quantity
• It is denoted by p = mv

For example, a ball of 1 kg moving at 10 m/sec has a momentum of 10 kg/sec.

The momentum of a system remains conserved. Therefore, Greater force is required to set heavier bodies in motion

Greater force is required to stop bodies moving with higher velocities

The greater the change in momentum in a given time, the greater is the force that needs to be applied. In other words, the greater the change in momentum vector, the greater the force applied.

“An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.”

For example,

• Water in a bottle continues moving forward even though the bottle has come to a halt.
• A ball lying on the table at rest will remain at rest until an external force is applied to it.
  
  

Balanced & unbalanced forces

Balanced Forces:

• Equal and opposite forces
• Do not cause any change in motion

Unbalanced Forces:

• Unequal forces
• Can be in the same or opposite direction
• Causes a change in motion

For example, if teams 1 and 2 apply equal forces in opposite directions during a tug of war, there would be no net force. This is a balanced force.
However, if Team 1 exerts more force than Team 2, then there would be a net movement towards Team 1 and Team 1 would win. This is an unbalanced force.

1. Aim: To understand the relationship between force and acceleration by pulling a 1 kg weight on a smooth surface.

2. Requirements: 1 kg weight, smooth wooden table, talcum powder, and measuring tools (for acceleration).

3. Procedure

• Place the 1 kg weight on the smooth wooden table. Sprinkle talcum powder evenly over the table to reduce friction.
• Pull the weight so that it moves with an acceleration of 1 m/s².
• Repeat by pulling the weight with a higher acceleration, say 2 m/s².
• Note that with 2 m/s² acceleration, the force applied is now 2 N.
• Take several trials to understand how changing acceleration affects the force required.

4. Conclusion: This experiment shows that the force required increases with acceleration. The relationship between force, mass, and acceleration is given by Newton’s second law.

Force (F) = Mass (m) × Acceleration

In this case:

• For 1 m/s² acceleration, the force applied is 1 N.
• For 2 m/s² acceleration, the force applied is 2 N.

Thus, force is directly proportional to acceleration for a given mass.