A bus pulling away: velocity and acceleration
A bus leaves the stop and speeds up steadily. Read its speedometer and the distance it has gone every 5 seconds, then make it speed up harder or start already moving.
Core concept
Acceleration is how fast velocity changes: v = u + at, so a steadily accelerating bus gains the same speed every second and covers more distance each second
Topic: Motion
Velocity is speed: How far something travels in a certain time, like kilometres per hour. All key words in a particular direction, measured in metres per second (m/s); a bus's speedometer shows it in kilometres per hour (1 m/s = 3.6 km/h). When a bus pulls away from a stop, its velocity goes up: it accelerates. Acceleration is the change of velocity each second, in metres per second per second (m/s²). If a bus accelerates at 1 m/s², it goes 1 m/s faster every second. Its velocity after t seconds is v = u + at, where u is the velocity it started with. Because it keeps getting faster, it covers more ground every second: the distance is s = ut + ½at².
What you will learn
- Explain velocity and acceleration, and their units.
- Use v = u + at to find the velocity of an accelerating bus.
- Explain why an accelerating bus covers more distance each second.
- Change a velocity from m/s into km/h.
Before you start
- Know that speed = distance ÷ time.
Materials
- A toy car and a ramp, or a bus ride with a phone speedometer app
Equipment
- A stopwatch and a measuring tape
Procedure
- Record the bus 10 s after it leaves the stop at 1 m/s².
- Record at 5 s, 15 s and 20 s as well.
- Make it accelerate at 1.5 m/s² and record at 10 s.
- Start it already moving at 5 m/s and record at 10 s.
How this simulation is simplified
- The bus accelerates steadily (the same acceleration all the time) along a straight, level road.
- 1 m/s = 3.6 km/h.