Glossary · Vật lý
Acceleration
The rate at which velocity changes with time. By Newton's second law, a body's acceleration is proportional to the net external force on it and inversely proportional to its mass.
Acceleration is a vector, so it has both a magnitude and a direction. A body that changes direction while holding its speed constant is still accelerating; uniform circular motion is the clearest case.
Newton's second law ties acceleration to its cause: the same force applied to twice the mass produces half the acceleration. This is the quantitative statement of what inertia describes qualitatively.
In everyday life, the lurch in your stomach or the push into your seat comes not from speed but from acceleration: travelling steadily at 300 km/h feels like nothing, while a sudden change of velocity at low speed is unmistakable.