Physics Form 4 -- Chapter 2

Analysing Linear Motion (直线运动分析)

1. - Distance - (距离)

Distance is a scalar quantity which has only magnitude but no direction

=距离是一个scalar quantity(标量)，但它只有大小没有方向

2. - Displacement - (位移,换置)

Displacement is a vector quantity which has both magnitude and direction . 

=位移是一个vector quantity(矢量) , 有大小和方向。

3. - Speed - (速度)

Speed is defined as the distance travelled per unit time

=速度定义为距离÷行驶时间

4. - Velocity - (速度)

Velocity of an object is defined as the distance per unit time in a specified direction . Velocity is measured in meter per second (m/s)

=一个物体的速度定义为在一个指定的方向的距离÷时间。

5. - Acceleration - (加速度)

Acceleration is defined as the rate of change of velocity with time . Acceleration is measured in meter per second second . (ms^-2) . Formula  (a= v-u/t)

=加速是定义为速度随时间的变化率。加速以每米一秒。

6. - Deceleration - (减速度)

Deceleration is defined as negative acceleration .

=减速被定义为负数的加速度。

*************************************************************************

(Ⅰ) An object is said to move with UNIFORM ACCELERATION if the rate of change of its velocity is constant .

=一个object，被称为''匀加速移动'' , 如果它速度的变化率是constant的。

(Ⅱ) An object is said to move with ZERO ACCELERATION if its velocity remains constant .

=一个object , 被称为是''零加速移动'' , 如果它的速度保持不变。

Ticker-Tape Timer (股票磁带计时器)

It is a narrow paper tape which can be passed through printing devices that place symbols ranging from simple dots to alpha-numeric symbols.

=这是一个狭窄的纸带可通过打印设备通过该地方的象征，从简单的点，以字母和数字符号

*Regardless of the type of recording timer used, the marks are made at regular time intervals.

=无论使用的类型的录音定时器，标记都是由定期的时间间隔而定。

*These time intervals are usually small fractions of second, and can be determined by comparing the number of dots made on a strip of paper tape as it is pulled through the timer to the number of seconds ellapsed (recorded by a stop watch) while the paper is being pulled.

= 这些时间间隔通常是第二小分数，并且可以通过比较以纸胶带条作出的点数，因为它是通过对经过的秒数（用秒表记录）而纸拉定计时器拉

a. Constant Speed or Velocity Examples: 

Ticker Tape: "Slower" speed

*   *   *   *   *   *   *   *   *  *  *  *  *  *  *  *  *  *  *

  
 

Ticker Tape: "Faster" speed

*         *         *          *         *         *         *         *           *           *            *            *             *         *

 

b. Acceleration, Increasing Speed or Velocity Examples:

Ticker Tape: "slower" acceleration

**  *    *       *           *                 *                       *                               *                                       *

  
 

Ticker Tape: "Faster" acceleration

**   *        *               *                        *                                   *                                       *

 

C. Deceleration, Decreasing Speed or Velocity Examples:

Ticker Tape: "slower" acceleration

**  *    *       *           *                 *                  *                   *                    *

  

  
 

Ticker Tape: "faster" deceleration

*                                          *                              *                   *           *      *   * *

* Each tick length then shows the distance covered in 0.2s and is therefore a measure of the average velocity during the time interval of 0.2s
=每个刻度的长度在0.2秒，然后显示所涉及的距离，因此时间间隔内的平均流速测量在0.2秒


* The four equation of linear motion are :
(i) V= u + at
(ii) V² = u² + 2as
(iii) s = ut + 1/2 at²
(iv) s = 1/2(u+v)t


Analysing Motion graphs (分析运动图)





** A car is travelling at constant speed
=汽车行驶在一个恒定速度





**A car is travelling with increasing velocity

=汽车是行驶速度增加

** A car is travelling with decreasing velocity

=汽车是行驶的速度递减

** A car is at rest (stationary)

=汽车是在休息（原地）

In a s-t graph, the velocity at any time is given by the slope of tangent to the graph at the instant. If the speed is uniform, the graph inclined straight line.

=在speed & time graph中，在任何时候给予的速度切线斜率在瞬间图。如果速度是均匀的，图形倾斜直线。

Speed - time graph ( v-t graph )
v-t graph gives the velocity of a moving object at different time. Here are 4 v-t graph representing the motion of 4 cars:
=一个移动的物体在不同时间的速度。这里有4个名词图代表了4辆汽车的议案


(a)



(b)



(c)



(d)



The acceleration at any time is given by the slope of tangent to the graph at that time
=在任何时候加

速度的切线斜率图

The area enclosed by the graph between a certain time interval represent the displacement of the car travelled during that time interval.

=在一定的时间间隔之间的封闭图形的面积代表在这段时间间隔行驶的汽车排量。

• ab : Object increases its velocity from rest. (Acceleration)
• =增加其速度。 （加速）
• bc : Object decreases its velocity to zero. (Deceleration)
• =降低它的速度为零。 （减速）
• cd: Object INCREASES its velocity from rest but it travel in REVERSE direction. (ACCELERATION)
• =增加其速度，但它在相反方向的走。 （加速）
• de: Object DECREASES its velocity to zero and it travel in REVERSE direction. (DECELERATION)
• =下降的速度为零，它在相反方向的走。 （减速）

Acceleration - time graph ( a-t graph )