Physical Science / Unit 7: Motion and Forces
7.1 Speed and Velocity
Notes
Speed is how fast an object moves: distance divided by time.
- $\displaystyle v = \frac{d}{t}$. Units: m/s or km/h. Rearranged: $d = vt$ and $\displaystyle t = \frac{d}{v}$.
- Velocity is speed with a direction (for example 20 m/s north). Velocity can change even if speed stays the same, such as when turning.
- Average speed $\displaystyle = \frac{\text{total distance}}{\text{total time}}$.
- Example: A car travels 150 km in 3 h. $\displaystyle v = \frac{150}{3} = 50$ km/h.
Practice
A runner covers 100 m in 20 s. What is her average speed?
$\displaystyle v = \frac{100}{20} = 5$ m/s.
A train moves at a constant 60 km/h. How far does it travel in 2.5 hours?
$d = vt = 60 \times 2.5 = 150$.
Which is a statement of velocity rather than speed?
Velocity includes direction.
Ready for more? Take the Unit 7 test.