When a body is said to be accelerated, what can we say about changes in its speed and direction of motion?

Introduction / Context:
Acceleration is a central concept in mechanics and is often misunderstood. Many learners think only about speeding up or slowing down, but acceleration actually describes any change in velocity. Because velocity is a vector quantity with both magnitude and direction, acceleration can result from changes in speed, changes in direction, or both. This question tests whether you clearly understand what must happen to a body that is accelerated and whether speed is required to change in every such case.

Given Data / Assumptions:

• A body is described as being accelerated.
• Acceleration is defined as the rate of change of velocity.
• Velocity includes both speed (magnitude) and direction.
• We have options concerning whether speed or direction must change under acceleration.

Concept / Approach:
Acceleration is given by a = dv/dt, where v is velocity. Because velocity is a vector, dv can arise from a change in the magnitude of velocity (speed), a change in its direction, or both simultaneously. For example, in uniform circular motion, the speed is constant, but the direction is continuously changing, so the body is accelerated purely because of the change in direction. In straight-line motion with increasing or decreasing speed, acceleration results from the change in magnitude. Therefore, it is not necessary that speed must always change when a body is accelerated; sometimes only direction changes.

Step-by-Step Solution:
Step 1: Recall that acceleration is defined as the rate of change of velocity, not just speed.Step 2: Recognise that velocity has both magnitude (speed) and direction.Step 3: Consider a body moving in a circle at constant speed; its direction changes at every point.Step 4: In this circular motion, there is acceleration (centripetal acceleration) even though speed remains constant.Step 5: In straight-line motion with changing speed, both speed and velocity magnitude change, giving acceleration.Step 6: Conclude that when a body is accelerated, its speed may or may not change; a change in direction alone is sufficient.

Verification / Alternative check:
Textbook examples of uniform circular motion clearly state that acceleration is present despite constant speed. Similarly, projectile motion involves both changes in speed and direction, showing that acceleration does not have a single simple effect on speed. A purely mathematical check using vector calculus also shows that if the direction of a velocity vector changes with time, then the derivative dv/dt is nonzero, indicating acceleration, regardless of whether the magnitude stays constant.

Why Other Options Are Wrong:
Saying that velocity never changes contradicts the very definition of acceleration. The statement that speed always changes ignores cases like uniform circular motion, where speed stays constant. The statement that direction always changes is also false, because in straight-line motion along a fixed direction, speed can change without changing direction, and the motion is still accelerated. Therefore, options A, B and C are all too restrictive or incorrect.

Common Pitfalls:
Many learners associate acceleration only with getting faster or slower, treating it as a scalar change in speed. Others memorise formulae without thinking about velocity as a vector. To avoid such misunderstandings, always think of acceleration as any change in velocity, including direction. This more complete picture helps you solve a wide variety of problems involving curving paths, circular motion and variable speeds.

Final Answer:
When a body is accelerated, its speed may or may not change; even a pure change of direction produces acceleration.