Lesson 1 of 4 | General Science / Physics basics
Motion, Speed and Velocity
1 practice test
Motion, Speed and Velocity
Physics is the branch of science that studies matter, energy, and how they interact. One of its first topics is motion — a change in an object's position with time.
Key concepts
- Distance is the total path length travelled (scalar). Displacement is the shortest straight-line distance from start to end, with direction (vector).
- Speed = Distance ÷ Time. SI unit: metre per second (m/s).
- Velocity = Displacement ÷ Time — speed in a given direction.
- Acceleration = Change in velocity ÷ Time. SI unit: m/s².
- To convert km/h to m/s, multiply by 5/18.
Worked example
Question: A train covers 180 km in 2 hours. What is its average speed in m/s?
Solution:
- Speed = Distance ÷ Time = 180 km ÷ 2 h = 90 km/h.
- Convert to m/s: 90 × 5/18 = 25 m/s.
Answer: The average speed is 25 m/s.
Analogy
Analogy: A walk to the market and back
Imagine you walk 2 km to the market and 2 km back home:
- Distance is what your step-counter shows: 4 km in total. It only cares how much you walked — a scalar.
- Displacement is how far you are from where you started: 0 km, because you are back home. It cares about direction — a vector.
- Speed = distance ÷ time. If the trip took 1 hour, your average speed was 4 km/h.
- Velocity = displacement ÷ time = 0 km/h for the round trip!
So a speedometer tells you speed, while a GPS arrow pointing "3 km north" is closer to velocity.