章节大纲

  • A roller coaster in a loop, showcasing twists and turns to illustrate acceleration.

    Imagine the thrill of riding on a roller coaster like this one! The coaster slowly crawls to the top of the track and then flies down the other side. It also zooms around twists and turns at breakneck speeds. These changes in and direction are what make a roller coaster ride so exciting. Changes in speed or direction are called acceleration.
    ::想象一下骑在像这样的过山车上时的刺激。 海岸车慢慢地爬到赛道的顶端, 然后飞到另一侧。 它还会放大曲折, 以断层速度旋转。 这些变化和方向使得过山车骑得如此刺激。 速度或方向的变化被称为加速。

     

    Defining Acceleration
    ::定义加速加速

    Acceleration is a measure of the change in of a moving object. It measures the rate at which velocity changes. Velocity, in turn, is a measure of the speed and direction of motion, so a change in velocity may reflect a change in speed, a change in direction, or both. Both velocity and acceleration are vectors . A vector is any measurement that has both size and direction. People commonly think of acceleration as an increase in speed, but a decrease in speed is also acceleration. In this case, acceleration is negative and called deceleration. A change in direction without a change in speed is acceleration as well.
    ::加速度是移动对象变化的量度。 它测量速度变化的速度。 速度是速度和运动方向的量度, 因此速度的变化可以反映速度的变化, 方向的变化, 或者两者兼而有之。 速度和加速度都是矢量。 矢量是具有大小和方向的任何测量。 人们通常认为加速是速度的增加, 速度的下降也是加速。 在这种情况下, 加速是负的, 称为减速。 加速是方向的改变, 速度没有变化, 加速也是加速。

    Q: Can you think of an example of acceleration that doesn’t involve a change in speed?
    ::问:你能想象一个不涉及速度变化的加速率的例子吗?

    A: Driving at a constant speed around a bend in a road is one example. Use your imagination to think of others.
    ::A: 在路弯曲处以恒定速度驾驶就是一个例子。用你的想象力来想象其他人。

    Examples of Acceleration
    ::加速实例

    You can see several examples of acceleration in the pictures from the Figure . In each example, velocity is changing but in different ways. For example, direction may be changing but not speed, or vice versa. Figure out what is moving and how it’s moving in each of the photos.
    ::您可以从图中看到一些加速的例子。在每一个例子中,速度都在变化,但方式不同。例如,方向可能正在变化,但不会变化,反之亦然。找出每张照片中移动的是什么以及它是如何移动的。

    Four examples of acceleration: carousel rider, marathon runner, skydiver, and basketball spinner.

    Q: Describe how velocity is changing in each of the motions you identified from the Figure .
    ::问题:描述您从图中发现的每项动作的速度变化。

    A: You should describe how both direction and speed are changing. For example, the boy on the carousel is moving up and down and around in a circle, so his direction is constantly changing, but his speed changes only at the beginning and end of the ride. The skydiver is falling straight down toward the ground so her direction isn’t changing, but her speed keeps increasing as she falls until she opens her parachute and she rapidly decelerates (slows down).
    ::甲:你应该描述一下方向和速度的变化。 比如,旋转木马上的男孩在旋转圈上上下移动,所以他的方向在不断改变,但他的速度只是在旅程的开始和结束时才会改变。 天空潜水器正直向地面下降,这样她的方向就不会改变,但是她的速度在不断加快,直到她打开降落伞并快速减速(减速 ) 。

    Feeling Acceleration
    ::感知加速

    If you are accelerating, you may be able to feel the change in velocity. This is true whether the change is in speed, direction, or both. You often feel acceleration when you ride in a car. As the car speeds up, you feel as though you are being pressed against the seat. When the car slows down, you feel like you are being pushed forward, especially if the change in speed is sudden. If the car changes direction and turns right, you feel as though you are being pushed to the left. With a left turn, you feel a push to the right. The next time you ride in a car, notice how it feels as the car accelerates in each of these ways. 
    ::如果您正在加速, 你也许能够感觉到速度的变化。 无论变化的速度、方向或两者都是如此。 当您乘坐汽车时, 您通常会感到加速。 随着汽车的加速, 您会感觉自己被挤压在座位上。 当汽车减速时, 您会感觉自己正在被推向前进, 特别是当速度的改变是突然的。 如果汽车改变方向和向右转, 您会感觉自己被推向左边。 左转时, 您会感到向右推动。 下次你坐汽车时, 注意汽车在车上加速的每一个方式。

    Use this simulation to further explore the acceleration of a model rocket due to gravity. Can you use the graphs to determine when the rocket is speeding up or slowing down?
    ::使用此模拟来进一步探索模型火箭因重力而加速的速度。 您能否使用这些图表来确定火箭在何时加速或减速?

     

     

    Summary
    ::摘要

    • Acceleration is a measure of the change in velocity of a moving object. It measures the rate at which the change is occurring. It may reflect a change in speed, a change in direction, or both. Like velocity, acceleration is a vector.
      ::加速度是测量移动对象速度变化的尺度。它测量变化发生的速度。它可能反映速度变化、方向变化或两者兼有。和速度一样,加速度是一个矢量。
    • Examples of acceleration include a person riding a carousel and a skydiver in free fall.
      ::加速度的例子包括骑旋转木马的人和自由坠落时的天空潜水员。
    • When you experience acceleration, you may be able to feel the changes in speed and/or direction.
      ::当你经历加速时,你也许能够感觉到速度和/或方向的变化。

    Review
    ::回顾

    1. Define acceleration.
      ::定义加速度。
    2. Describe an example of acceleration and explain how velocity is changing.
      ::描述加速的实例,并解释速度是如何变化的。
    3. The skydiver pictured in the Figure will soon open her parachute. How will her velocity change when the parachute first opens? 
      ::数字中的天花板将很快打开她的降落伞。 当降落伞第一次打开时,她的速度会如何变化?