Lesson · P.1.2

Acceleration

How acceleration measures a change in velocity over time using a = (v_f - v_i) / t, why a negative result simply means deceleration, and the constant free fall rate g = 9.8 m/s² that the HESI A2 physics subtest tests directly.

ObjectiveP.1.2Read4 minExam weightMotion ≈ 24% of Physics

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What you will be able to do

You can calculate acceleration from an initial velocity, a final velocity and a time, using a = (v_f - v_i) / t.
You can explain why a negative result from that formula means deceleration rather than a mistake, and read the direction of an acceleration correctly.
You can apply g = 9.8 m/s² as the constant acceleration of any object in free fall and use it in a calculation.

What the lesson concludes

Acceleration is the rate at which velocity changes over time: a = (v_f - v_i) / t.
The unit of acceleration is metres per second squared, m/s², because it is a velocity divided by a time.
Deceleration is not a separate formula. It is acceleration that works out negative because the final velocity is smaller than the initial velocity.
Every object in free fall near Earth's surface accelerates at the same constant rate, g = 9.8 m/s², regardless of its mass.
Rearranging a = (v_f - v_i) / t lets you solve for a final velocity or for a time whenever the other two quantities are known.