Revision: Motion in One Dimension Physics (English Medium) ICSE Class 9 CISCE

• 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.

• 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.

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

The distance covered by a body in a unit time is called its speed. It is also defined as the rate of change position of a body in any direction.
Speed = distance/time

Speed is the rate of change of distance.
Formula: Speed = distance /time
Unit is meter/second (m/s)

“Rate of change of displacement with time is called velocity.”
OR
“The time rate of change of displacement of an object is called the velocity.”
V = distance/time

Velocity is the rate of change in displacement.
Formula: Velocity (v) = displacement / time
SI unit of velocity is meter / second (m/s).

Velocity is the rate of change of displacement. It is the displacement in unit time.

Positive acceleration:
If the velocity of an object increases with respect to time, then the object is said to be in positive acceleration or just acceleration.

Negative acceleration or deceleration or retardation:
If the velocity of an object decreases with respect to time, then the object is said to be in negative acceleration or deceleration, or retardation.

The gravitational force due to the earth on a body results in its acceleration. This is called acceleration due to gravity and is denoted by ‘g’.

The ratio of the total distance travelled in a specified direction to the total time taken by the body to travel the distance is called average velocity.
Example: If you walk to a campsite 1 km away and then back to your starting point within 1 hour, then your average velocity will be zero because your initial and final position is the same.

When a body covers equal distances in equal intervals of time (however small may be the time interval) in a specified direction, the body is laid to be moving with uniform velocity.
Example: A car moving on a straight road with constant speed has uniform velocity.

The value of the acceleration due to gravity (g) on the surface of the Earth is given by the formula:

Where:

• g = Acceleration due to gravity (in m/s²).
• G = Newton's Universal Gravitational Constant (≈ 6.67 × 10⁻¹¹ N · m² / kg²).
• M = Mass of the Earth (≈ 6 × 10²⁴ kg).
• R = Radius of the Earth (≈ 6.4 × 10⁶ m).