Speed describes movement right now.
Velocity includes both speed and direction. Acceleration describes how velocity changes over time. An upward-moving car can accelerate upward while speeding up or accelerate downward while slowing down.
Deceleration is a familiar name for reducing speed, rather than a separate physical quantity.
A change in speed takes time.
Average acceleration is (1 − 0) ÷ 2 = 0.5 m/s². This average does not tell us whether acceleration changed smoothly during those two seconds.
Jerk describes changing acceleration.
Jerk is the rate of change of acceleration, measured in m/s³. Abrupt changes in acceleration can feel like jolts even when the maximum speed is modest.
A shaped motion profile introduces and removes acceleration progressively. This helps manage comfort and mechanical loading.
Think about the transitions.
- Build speedIntroduce acceleration, then ease it away.
- TravelHold speed where journey distance permits.
- Slow and stopShape deceleration and approach the landing.
An S-shaped velocity profile rounds the transitions compared with an ideal straight ramp. It does not mean the car follows an S-shaped physical path.
Comfort depends on more than one setting.
Available torque, load balance, mechanical condition, brake timing and feedback affect how closely actual motion follows the requested profile.
Gentler acceleration can require more time or distance to reach a speed. Journey planning must consider the available travel, rather than treating comfort settings independently.
A closer look
Distance travelled is the area under a velocity–time graph. For constant acceleration from rest to 1 m/s over two seconds, the triangular area is one metre. A differently shaped profile must be assessed using its own area.
Check your understanding
Can two journeys reach the same speed with different ride comfort?
Reveal the explanation
Yes. Their acceleration and changes in acceleration can differ, as can the mechanical response. Maximum speed alone does not describe the ride.