Video Lesson

Video

Lesson Objective

Dear Learners,

At the end of this section, you should be able to:

• Define acceleration;
• Calculate the average acceleration of a body if its velocity changes from
  some initial value to final value in a given time.
• Define uniform motion;
• Give examples of uniform motion.

Brainstorming Question

If the initial and final velocities of a car are the same, what will be its
acceleration?

key terms and concepts

Acceleration

Acceleration is defined as the rate of change of velocity of an object with respect to time. It indicates how quickly an object is speeding up or slowing down. Acceleration is a vector quantity, meaning it has both magnitude and direction. Mathematically the instantaneous velocity is given:

 Acceleration(a) = Δv / Δt​ = V_f -V_i / Δt

Where Δv is the change in velocity, V_f  is final velocity, V_i is initial velocity  and Δt is the time interval over which the change occurs. The standard unit of acceleration is meters per second squared (m/s²).

Characteristics:

• Positive Acceleration: When an object speeds up in the direction of motion i.e (V_f > V_i)
• Negative Acceleration (Deceleration): When an object slows down; also known as deceleration. i.e (V_f < V_i)
• Zero Acceleration: When an object moves with a constant velocity. i.e ( V_f =V_i)

Examples:

A train moving in the east direction accelerates from rest to 36km/h in 20s. What is the average acceleration during that time interval?

Given:

V_i =0, V_f=36km/h = 10m/s, ∆t=20 s, Required: a_av =?

Solution:

a_av = V_f -V_i/ ∆t = 10 m/s −0/ 20 s = 0.5m/s²

Uniform Motion

• Uniform motion refers to the movement of an object at a constant speed in a straight line.

Characteristics:

• Constant Speed: The object covers equal distances in equal intervals of time.
• Zero Acceleration: Since the speed is constant, there is no change in velocity, resulting in zero acceleration.

Examples:

• A car cruising at a steady speed of 60 km/h on a straight highway.
• A train moving at a constant speed on a straight track.

• Acceleration is the rate of change of velocity.
• Motion at a constant velocity or uniform motion means that the position of the object is changing at the same rate.