AP力学考试实验题怎么答？控制变量法原来是关键

很多同学都对AP力学考试实验题感到懵懵的，本文就结合2020年CB官方出的一道例题，来告诉大家AP力学考试看重什么样的实验理念。虽然去年考试情况特殊，题目要求可能会与今年的有所不同，但从时效性上来说，还是很值得参考的。

AP力学考试简介

AP物理C分为单独的两门考试——AP物理C力学和电磁学。这两门考试相对于以上两门偏难，且都需要依赖于微积分的知识进行解题，需要考生对高数有一定的了解。

AP物理C力学相当于大学学期的一门以微积分为基础的物理课程，难度较高，课程涵盖运动学、牛顿运动定律、粒子和线性动量系统、圆周运动和旋转、振动及引力，功、能量以及功率等知识。学员必须具有微积分基础，如果你正在准备AP微积分，这门考试建议同学们不要错过。

AP物理C力学考试时间为1.5小时，考试分为以下两部分：部分：35道选择题，45分钟，占总分的50%

第二部分：3个简答题，45分钟，占总分的50%

2020年AP力学考试实验题例题

题目:

Students are asked to perform an experiment to determine g , the acceleration due to gravity, in the lab using the setup shown. They are expected to find g by plotting their data in a graph. The students have access to equipment commonly found in a high school physics laboratory, but the experiment must use the setup as shown above which includes a cart of mass M on an ramp which is set at an angle ѳ to the horizontal. The cart is held on the ramp by a spring of known constant k . There is negligible friction between the cart and the ramp.

(a) Briefly identify each quantity to be measured, the symbol used to represent that quantity, and the equipment that would be used to measure the quantity.(b)

Briefly describe the procedure to be used to determine the acceleration due to gravity. Provide enough detail so that another student could replicate the experiment, including any steps necessary to reduce experimental uncertainty. As needed, use the symbols defined in part (a).

(c) Which quantities that were measured in part (b) could be graphed on the horizontal and vertical axes to produce a graph that would be used to determine the acceleration due to gravity?

(d)Describe what information from the graph described in part (c) would be used and how it would be used to determine the acceleration due to gravity.

2020年AP力学考试实验题样题解析：

(a) Briefly identify each quantity to be measured, the symbol used to represent that quantity, and the equipment that would be used to measure the quantity. 

Solution：

Mass of the cart M by electronic balance

Original/final length of the spring X1,X2 with meterstick

Angle Ɵ using protractor

b) Briefly describe the procedure to be used to determine the acceleration due to gravity. Provide enough detail so that another student could replicate 

the experiment, including any steps necessary to reduce experimental uncertainty. As needed, use the symbols defined in part (a). 

Solution:

1.Measure the original length  X1 of the spring 

2.Set up the ramp with an angle Ɵ to the horizontal and measure Ɵ with protractor.

3.Place the the cart with spring on the ramp.

4.Measure the length X2 of the spring while cart is at rest on the ramp.( The spring has been stretched by cart now)

5.Repeat  step 3，4，5 with different M five times.

6.Draw a best fit line with data in the graph of DeltaX vs. M. 

(c) Which quantities that were measured in part (b) could be graphed on the horizontal and vertical axes to produce a graph that would be used to determine the acceleration due to gravity? 

Solution: 

Horizontal axis: M 

Vertical axis: Delta X= (X2-X1) 

(d) Describe what information from the graph described in part (c) would be used and how it would be used to determine the acceleration due to gravity.

Solution:

Slope of the graph should be used to determine g, acceleration of gravity.

Since MgsinƟ =k*DeltaX,  we can deduce that g=k*DeltaX/MsinƟ, the slope of graph is gsinƟ/k , then we can determine g,  g=slope*k/sinƟ (k is known, Ɵ has been meaured.)

(e) In a second experiment students place a different cart of unknown mass on the ramp and attach it to the spring, letting the cart and spring come to rest. 

The cart is then displaced slightly down the ramp and released, causing the cart to oscillate on the ramp. The students create the position vs. time graph 

shown above using a motion sensor. Briefly describe how the students could use the graph to determine the mass of the new cart. 

Solution :

Although it is a damped oscillation, the period of oscillation is fixed which can be judged by the graph, T=1s. and according to the equation of T=2.pi sqrt(M/k) , we can get M=K*T^2/4*pi^2

以上公式是按照今年官网给出的用电脑键盘直接作答时候，字母、特俗符号的输入方式要求作答的。

这道AP力学考试的实验题设计样题，它给你提供了一个实验考察的方向指引，没有知识上的偏向性，甚至可以说不太可能去考察这个知识点。为什么？太简单了，这就是纯粹为了告诉大家实验题是一个什么样子的题目而已。更何况，这个题目的（e）涉及到的知识点，在当年的考纲里面已经明确删除了。

但是通过这道题，我们还是能够读出一些重要信息的。例如：AP力学考试想考察的实验理念。

首先，就是控制变量法，待测物理量由多个变量决定的时候，我们当然是要控制变量，逐一研究待测物理量分别与每一个自变量之间的关系。其次，利用图像处理数据。在图像处理数据，选取点的时候，注意选取的是非实验数据点，这是因为作出的best-fit-line的主要目的是，多次测量取平均值，减小偶然误差。

同时，我们在图像处理数据的时候，智慧地设定坐标轴，画出线性回归曲线，再利用图像的斜率，求出需要的物理量。多次测量减小偶尔误差。完善实验原理解决系统误差。

自行练习，可考虑测摩擦因数，测转动惯量，测加速度。验证动量守恒定律，机械能守恒定律，角动量守恒定律。阿特伍德机以及变形的应用。

需要熟悉的仪器，force sensor，motion sensior, timer, photogate, airtrack.

涉及到微积分的有空气阻力的运动，转动动能，连续体的转动惯量等还是需要考前认真再看一下的。平动和转动的牛顿第二定律结合问题，也是考察重点。

AP力学考试实验样题就分享到这里，希望能帮你更好地认识CB的出题套路。

今年的AP考试和去年一样特殊，一来是采取网考和线下考试并行的方法，二来也是2019年AP改革后新考纲的首次考试。如果你还不知道怎么针对性复习，可以点击预约试听【唯寻AP复习冲刺班】——

唯寻教学天团授课，

对知识模块进行高速梳理，

准确狙击必考重点，

帮助学员构建思维模型，

完美拿捏AP灵活的考察体系，

网考、线下考试都一样锁定5分。    

更多AP复习攻略点击    

2021AP世界史网考与纸考的区别，如何复习才能快速适应？    

会考的AP物理C考点和公式 都在这里了