Motion in a Straight Line – Kinematics

Vocabulary flashcards covering key terms and formulas from the lecture on one-dimensional motion and basic kinematics.

Kinematics

The branch of mechanics that studies the motion of bodies without considering the causes of motion.

Rest

The state in which a body’s position does not change with time relative to a chosen observer.

Motion

The state in which a body’s position changes with time relative to a chosen observer.

Distance (d)

The total length of the path travelled by a body during its motion; a scalar quantity (SI unit: metre, m).

Displacement

The shortest straight-line distance from the initial to the final position of a body, measured in a specific direction; a vector quantity (SI unit: metre, m).

Revolution

One complete turn around a circular path; distance in one revolution = 2πR, while displacement after one full revolution is zero.

Speed (v)

The ratio of the distance travelled to the time taken (v = d/t); a scalar quantity (SI unit: metre per second, m s⁻¹).

Uniform Speed

Motion in which a body covers equal distances in equal time intervals.

Non-uniform Speed

Motion in which a body covers unequal distances in equal time intervals (or equal distances in unequal time intervals).

Average Speed (v_avg)

Total distance travelled divided by total time taken: v_avg = Σd / Σt.

Kilometre–metre Conversion

1 kilometre (km) = 1000 metres (m).

Mile–kilometre Conversion

1 mile ≈ 1.6 kilometres (km).

km h⁻¹ to m s⁻¹ Conversion

1 km h⁻¹ = 5⁄18 m s⁻¹; conversely, 1 m s⁻¹ = 18⁄5 km h⁻¹.

Average Speed for Two Equal Half-Distances

If the first half of a trip is travelled at speed v₁ and the second half at v₂, the average speed is v_avg = (2 v₁ v₂)/(v₁ + v₂).

Average Speed for Three Equal Third-Distances

If successive one-third distances are covered at speeds v₁, v₂ and v₃, the average speed is v_avg = 3 / (1/v₁ + 1/v₂ + 1/v₃).