Physical Science / Unit 7: Motion and Forces
7.2 Acceleration
Notes
Acceleration is the rate at which velocity changes. It happens when an object speeds up, slows down or changes direction.
- $\displaystyle a = \frac{v_f - v_i}{t}$. Units: $\text{m/s}^2$.
- Example: A car goes from 0 to 20 m/s in 4 s. $\displaystyle a = \frac{20 - 0}{4} = 5 \text{ m/s}^2$.
- Slowing down gives a negative acceleration (deceleration).
- Turning at constant speed is acceleration because direction changes.
Practice
A cyclist speeds up from 2 m/s to 8 m/s in 3 s. What is the acceleration?
$\displaystyle a = \frac{8 - 2}{3} = 2$.
A car moving at constant speed goes around a curve. Is it accelerating?
Acceleration is any change in velocity, including direction.
A ball slows from 12 m/s to 0 in 4 s. What is its acceleration?
$\displaystyle a = \frac{0 - 12}{4} = -3$.
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