Free-fall acceleration

Active vocabulary

free fall

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вільне падіння

free-fall (gravity) acceleration

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прискорення вільного падіння

If you threw an object either up or down and could somehow eliminate the effects of air on its flight, you would find out that the object accelerates downward at a certain rate. That rate is called the free-fall acceleration g. The acceleration is independent of the object's characteristics, such as mass, density, or shape; it is the same for all objects.\

The equations of motion for constant acceleration in Table 1 are applied to free fall near the Earth's surface. That is, they are applied to an object in vertical flight, either up or down, when the effects of air can be neglected. However, we can make them simpler to use with two minor changes. (1) The directions of motion are now along the vertical y axis instead of the x axis, with the positive direction of y upward. (2) The free-fall acceleration is now negative, that is, downward along the y axis, and so we replace a with — g in the equations.

With these small changes, Equations of Table 1 become, for free fall, Equations in Table 1.2. Note carefully that: the free-fall acceleration near the Earth's surface is a = — g = —9.8 m/s², and the magnitude of the acceleration is g = 9.8 m/s². Do not substitute —9.8 m/s² for g.

Table 1.2

equation	missing quantity

Imagine you throw a ball directly upward at an initial velocity and then catch it when it returns to the level of starting point. During its free-fall flight(just after its release and just before it is caught), the equations of Table 2 are applied to its motion. The acceleration is always a = -g = -9.8 m/s² and alike downward. The velocity, however, changes: during the moving up, the magnitude of the (positive) velocity decreases, until it is momentarily zero. Because the ball has stopped, it is at its maximum height. During the moving down, the magnitude of the (negative) velocity increases.

Дата добавления: 2015-11-16