Vector Addition

While the vector addition discussed in Chapter 3 involves displacement vectors, vector addition can be applied to any type of vector quantity.

Acceleration at the Highest Point

many people claim that the acceleration of a projectile at the topmost point of its trajectory is zero. This mistake arises from confusion between zero vertical velocity and zero acceleration. If the projectile were to experience zero acceleration at the highest point, then its velocity at that point would not change-the projectile would move horizontally at constant speed from then on! This does not happen, because the acceleration is NOT zero anywhere along the trajectory.

Acceleration of a Particle in Uniform Circular Motion

Remember that acceleration in physics is defined as a change in the velocity, not a change in the speed (contrary to the everyday interpretation). In circular motion, the velocity vector is changing in direction, so there is indeed an acceleration.

Centripetal Acceleration is not Constant

We derived the magnitude of the centripetal acceleration vector and found it to be constant for uniform circular motion. But the centripetal acceleration vector is not constant. It always points toward the center of the circle, but continuously changes direction as the object moves around the circular path.

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