If a body in linear motion changes from point P to Q, the motion is

Analyze the question

A body in linear motion moves from point P to point Q along a straight line. We need to name the type of motion.

Explain the concept

• Translational motion: every part of the body moves the same distance in the same direction at the same time. The body moves from one place to another, usually along a straight path (linear) or a curved path.
• Rotational motion: the body spins about an axis, as in a wheel or a fan.
• Simple harmonic motion (SHM): the body oscillates to and fro about a fixed point, with acceleration proportional to displacement and directed towards that point.
• Circular motion: the body moves along a circular path around a centre.

Solution

1. The body moves in a straight line, which rules out circular motion (D) and rotational motion (B).
2. It goes from P to Q only. It does not oscillate back and forth about a mean position, so it is not simple harmonic (C).
3. The body changes its position from one point to another without spinning, and that is translational motion.

Linear motion is a special case of translational motion, so the answer is A.

Answer: A. Translational

Exam tip

Match the keyword to the motion:

• Translation = "travel" from one place to another
• Rotation = "spin" about an axis
• Oscillation/vibration = "to and fro" (SHM)
• Circular = "round a centre"

If the question says "from point P to Q", think translational.