Revision: Motion, Force and Work Science SSC (English Medium) 7th Standard Maharashtra State Board

The length of path travelled by a body in certain interval of time is called distance.

Displacement of an object between two points is the shortest distance between these two points.
“It is the unique path that can take the body from its initial to the final position.”

The displacement of a moving body is defined as the change in its position along a particular direction

• Displacement is the shortest distance in a straight line between the starting point and the final point, along with a direction. It is a vector quantity, meaning it includes both magnitude (distance) and direction.
• Example: In Ranjit’s case, the displacement is the straight line AD from his house to the school.

• Distance is the total length of the path travelled by a moving object, regardless of the direction. It is a scalar quantity, which means it only has magnitude (size), not direction.
• Example: If Ranjit walks from point A to B to C to D, the distance is the total of AB + BC + CD.

Speed is the distance travelled by an object in a given amount of time without considering the direction.

Formula: Speed = `"Distance traversed" / "Total time."`​

\[\vec F\] = m \[\frac{d\vec{\mathrm{v}}}{dt}\] = m\[\vec a\] ... (for constant mass)

Thus, if \[\vec F\] = 0, \[\vec v\] is constant. Hence, if there is no force, velocity will not change. This is nothing but Newton's first law of motion.

Statement:

Every inanimate object continues to be in a state of rest or of uniform unaccelerated motion along a straight line, unless it is acted upon by an external, unbalanced force.

Importance:

• It shows the equivalence between the state of rest and the state of uniform motion along a straight line — the distinction lies only in the choice of frame of reference.
• It defines force as a physical entity that brings about a change in the state of motion or rest of an object.
• It defines inertia as a fundamental and inherent property of every physical body by virtue of which it resists any change in its state of rest or uniform motion along a straight line.

• Newton's First Law states that a body at rest or in uniform motion stays that way unless an external unbalanced force acts on it.
• The law explains inertia, which is an object's resistance to changing its state of motion on its own.
• The 'state of rest' and 'state of uniform motion' are considered equivalent; both require a net unbalanced force to change.
• Force is defined by the law as the entity that changes a body’s state of motion.
• A balanced force results in a net force of zero, meaning no acceleration.
• An unbalanced force results in a net force that causes acceleration and changes the state of motion.
• Inertia is quantitatively measured by the object's mass (inertial mass).