The following is an exclusive excerpt from the book Developing Speed , published by Human Kinetics. All text and images provided by Human Kinetics. Acceleration and maximum speed are terms used in speed development programs, and when developing a program, it is vital to differentiate between them.
This allows coaches to target their training to the capacity most important in their own sport. Acceleration is the rate of change of velocity, or how quickly an athlete can increase the velocity of the motion. Maximum speed is the highest rate of speed an athlete can attain. Acceleration refers to velocity, and because velocity has both a magnitude and direction associated with it, acceleration changes when athletes change the magnitude of their motion how fast they are running , the direction of their motion, or both.
In terms of running, anytime the body starts, speeds up, or changes direction, it is accelerating. Given the number of direction changes in most sports, together with the number of times the rate of velocity needs to change, then clearly acceleration plays a crucial role in speed performance in sport.
This is further emphasized by the fact that elite sprinters have been shown to take up to 60 meters to reach top speed, and while this distance is normally shorter for field sport athletes, it still takes a considerable distance for most athletes to reach their maximum speed.
Given the typical distances run in sport and the limits of court dimension in other sports, such as tennis and basketball, acceleration may play a more important role than maximum speed in these sports. Terminal velocity Near the surface of the Earth, any object falling freely will have an acceleration of about 9.
Three stages of falling There are three stages as an object falls through a fluid: at the start, the object accelerates downwards due to the force of gravity as the object's speed increases, frictional forces such as air resistance or drag increase at terminal velocity, the weight of the object due to gravity is balanced by the frictional forces, and the resultant force is zero The weight of an object does not change as it falls, as long as it stays whole.
A skydiver The diagram shows what happens to the speed of a skydiver from when they leave the aircraft, to when they reach the ground after their parachute opens. Before the parachute opens: Immediately on leaving the aircraft, the skydiver accelerates downwards due to the force of gravity.
There is no air resistance acting in the upwards direction, and there is a resultant force acting downwards so the skydiver accelerates towards the ground. As the skydiver gains speed, their weight stays the same but the air resistance increases. There is still a resultant force acting downwards, but this gradually decreases. Eventually, the skydiver's weight is balanced by the air resistance. There is no resultant force and the skydiver reaches terminal velocity.
Velocity-time graphs for falling objects The diagram shows a velocity-time graph for an object falling through a fluid, eg air, water, oil. Between A and B The object accelerates at first because of the force of gravity. Between B and C The object is still accelerating but its acceleration decreases as time goes by. Keep in mind that this process happens in any gas or fluid. So terminal velocity defines the speed that a rock sinks when you drop it in the water. But they can increase their speed tremendously by orienting their head towards the Earth — diving towards the ground.
The gravity of the Earth pulls at you with a constant acceleration of 9. The opposing force of the atmosphere is called drag.
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