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Physics
Speed, Velocity & Acceleration
Speed, Velocity, and Acceleration
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Speed, velocity, and acceleration describe how objects move, from a cyclist on a path to a car entering a highway. Speed tells how fast something is moving, while velocity also includes direction. Acceleration tells how quickly velocity changes, which can mean speeding up, slowing down, or turning. These ideas help students understand motion in sports, transportation, amusement rides, and everyday travel.
Key Facts
- Speed = distance / time
- Velocity = displacement / time, with direction included
- Acceleration = change in velocity / time
- Average speed = total distance / total time
- If an object moves at constant velocity, its acceleration is 0 m/s²
- On a distance-time graph, steeper slope means greater speed
Vocabulary
- Speed
- Speed is how fast an object moves, measured as distance traveled per unit of time.
- Velocity
- Velocity is speed in a specific direction.
- Acceleration
- Acceleration is the rate at which an object's velocity changes.
- Distance
- Distance is the total length of the path an object travels.
- Displacement
- Displacement is the straight-line change in position from start to finish, including direction.
Common Mistakes to Avoid
- Confusing speed and velocity: speed has no direction, but velocity must include direction such as 12 m/s east.
- Using distance when displacement is needed: distance is the total path length, while displacement depends only on the start and end positions.
- Thinking acceleration only means speeding up: acceleration also happens when an object slows down or changes direction.
- Ignoring units: answers like 10 or 3 are incomplete because motion quantities need units such as m/s, km/h, or m/s².
Practice Questions
- 1 A cyclist travels 240 meters in 30 seconds. What is the cyclist's average speed in m/s?
- 2 A car changes velocity from 10 m/s east to 25 m/s east in 5 seconds. What is its acceleration?
- 3 A runner moves around a circular track and returns to the starting line. Explain how the runner's distance and displacement are different at that moment.