Velocity is speed with direction. The symbol for velocity is $\overrightarrow {v}$, but often the overhead arrow is ignored.

Acceleration ($\overrightarrow {a}$) is measured as the change in velocity over change in time. $$acceleration=\dfrac {change-in-velocity}{time}$$

$$a=\dfrac {v_{2}-v_{1}}{t_{2}-t_{1}}$$ where

a is the acceleration

v_{2 is the final velocity}

v_{1 is the initial velocity}

t_{2 - }t_{1} is the time taken for the velocity change

A body moving at a constant speed has no acceleration, because the change in velocity is zero.

Deceleration is negative acceleration. It occurs when a moving object slows down.

Distance is a measure of the actual route between two points. It is a **scalar** quantity.

Displacement is the shortest path between the two points. It is a **vector** quantity.

Scalar is one-dimensional; it has only magnitude. Vector is two-dimensional.; it has both magnitude and direction.

The S.I. unit of distance and displacement is meter (m).

Speed of a moving object is the distance moved in a time interval.

Mathematically, speed is the distance moved over the time taken.

$$speed=\dfrac {distance}{time}$$

If the distance is measured in metres and the time in seconds, then the speed is measured in S.I. unit as metres per second $\dfrac {m}{s}$

A car covers a distance of 10km in 15 minutes. Find its speed in metres per second.

10 km = 10 x 1000 m = 10000m

15 minutes = 15 x 60 seconds = 900s

Therefore, speed = $\dfrac {10000}{900}=11.11m/s$

Average speed is total distance divided by total time. It is also measured as the displacement over time.

Velocity is also measured as distance over time. Velocity is a vector quantity: it has both magnitude and direction. Speed, on the other hand, is scalar: it has only magnitude. The S.I. unit for speed as well as for velocity is the same: m/s.

A distance-time graph with uniform velocity is a straight line on the graph.

The distance-time graph with different velocities at different times is a curve.

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