Distance and speed

---

Average speed

The average speed of a moving object can be calculated using the formula:

$$\begin{array}{rl}\text{Average speed}& =\frac{\text{Distance}}{\text{Time}}\\ v& =\frac{\Delta x}{\Delta t}\end{array}$$

Note:

The greek delta ($\Delta$) symbol is used to represent change in.

Distance time graphs

Graphs can be used to represent the motion of object.

• Distance is plotted on the y axis. (Vertical)
• Time is plotted on the x axis. (Horizontal)
• The speed is equal to the gradient of the graph
• A horizontal line indicates that the object is stationary.

$$\begin{array}{rl}\text{Distance change}\Delta x& =1200-600=600m\\ \text{Time change}\Delta t& =60-30=30s\\ v=\frac{600}{30}& =20m{s}^{-1}\end{array}$$

Displacement time graphs

Graphs of displacement are to show how an object is displaced over time.

• Displacement is plotted on the y-axis
• Time is plotted on the x-axis

Varying speed and displacement

Naturally object do not instantly gain speed, and will have a period of time where the object is speeding up and accelerating.

$$\begin{array}{rl}\text{Speed equation:}& \\ v& =\frac{\Delta d}{\Delta t}\\ \text{Example values given below:}& \\ \Delta d& =300\\ \Delta t& =60\\ v=\frac{300}{60}& =5m{s}^{-1}\end{array}$$

---

See also

• INSERT

References

• A Level Physics OCR (Pages 22-26) BOOK