Vecteurs d'accélération

Speed is how fast an object moves, while acceleration is the rate of change in velocity. Acceleration occurs when velocity changes in magnitude, direction, or both. A runner traveling at constant speed but changing direction is accelerating, even though their speed remains the same. Acceleration is a vector quantity pointing in the direction of the velocity change.

Average acceleration is calculated as the change in velocity divided by the change in time: a = Δv/Δt. The change in velocity is found by subtracting the initial velocity vector from the final velocity vector. The direction of average acceleration points in the same direction as the change in velocity. This ratio gives the rate at which velocity changes over a time interval.

Instantaneous acceleration is the acceleration at a specific moment in time, found when the time interval approaches zero. As Δt becomes infinitesimally small, average acceleration approaches instantaneous acceleration. Instantaneous acceleration can be obtained from the derivative of the velocity function with respect to time. Average acceleration describes change over a finite interval, while instantaneous acceleration describes change at a precise instant.

Yes. An object accelerates whenever its velocity changes in direction, even if speed remains constant. A car traveling at constant speed around a curve is accelerating because its direction changes. Since velocity is a vector with both magnitude and direction, a change in either component constitutes acceleration. Direction change alone is sufficient to produce acceleration.

The direction of acceleration vectors always aligns with the direction of velocity change. When you subtract initial velocity from final velocity vectors, the resulting change in velocity determines the acceleration direction. This relationship holds whether the object speeds up, slows down, or changes direction. The acceleration vector points toward the direction the velocity is changing.

A drag racer experiences large acceleration immediately after starting but acceleration tapers off as the vehicle approaches constant velocity. Acceleration varies significantly with time during motion because the rate of velocity change decreases. Once the racer reaches constant velocity, acceleration becomes zero. Average acceleration over the entire race differs from instantaneous acceleration at any particular moment.

No. Acceleration has nothing to do with an object's size or mass. Two objects of different masses can have identical accelerations if their velocities change at the same rate. Acceleration depends solely on how quickly velocity changes over time, not on the physical properties of the object. This independence makes acceleration a fundamental kinematic quantity independent of object characteristics.