Physics-+speed,+velocity,+and+acceleration

__Speed__ is the rate of motion, or the rate of change of position. It is expressed as distance moved (d) per unit of time(t). Speed is a scalar quantity with dimensions distance/time. Speed is measured in the same physical units of measurement as __velocity__, but does not contain an element of direction. Speed is thus the magnitude component of velocity. Velocity contains both the magnitude and direction components. //Common speeds of// // moving objects // For human beings, an average walking speed is about 3 mph (~5 km/h, 1.39m/s), The speed of long distance jogging for average persons is about 6 mph (~10 km/h, 2.7 m/s). Top athletic sprinters can run at 23.03 mph (~36.85 km/h, 10.24 m/s) within a short distance such as a 200 meters dash. Cycling can average 12 mph (~20 km/h, 5.56 m/s) Car can average 65 mph (~104 km/h, 28.9 m/s ) on highway A 747 Airplane has an average speed 565 mi/hr **Acceleration** Acceleration, (symbol: a) is defined as the rate of change of velocity. It is thus a vector quantity with dimension length/time². In SI units, acceleration is measured in meters/second². To accelerate an object is to change its velocity, which is accomplished by altering either its speed or direction (like in case of uniform circular motion) in relation to time. A cceleration can have positive and negative values. Any time that the sign (+ or -) of the acceleration is the same as the sign of the velocity, the object will speed up. If the signs are opposite, the object will slow down. Acceleration is a vector quantity. When either velocity or direction changes, there is acceleration (or deceleration). To accelerate an object requires the application of a force.
 * Speed or Velocity?**

The graph of velocity (m/sec.) vs. time (sec.) is a straight line for accelerating objects. acceleration = velocity / time

 The graph of distance (x) vs. time (t) is a curve where the equation of motion is: x = 1/2 at²