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Lab Assignment 3:  Newton’s Laws

Instructor’s Overview

Newton’s laws of motion are a central component of our understanding of physics.  As we discussed in Module 5, Newton’s laws can be summarized as follows:

  1. Inertia – An object tends to resist changes in its motion.
  2. Relationship between the mass of an object, the net applied force, and the resulting acceleration – F = m ´ a.
  3. Action-reaction pairs – Forces come in pairs.

In this lab, you will perform experiments to explore each of the laws of motion.

This activity is based on Lab 5 of the eScience Lab kit.  Although you should read all of the content in Lab 5, we will be performing a targeted subset of the eScience experiments.

Our lab consists of three main components.  These components are described in detail in the eScience manual (pages 55-61).  Here is a quick overview:

  • In the first part of the lab, you will use a bowl full of water to understand the concept of inertia.  (eScience Experiment 1)
  • In the second part of the lab, you will recreate a classic physics experiment, the Atwood Machine.  This system consists of a pulley holding a string with two unequal masses.  Experimenting with an Atwood Machine is an excellent way to understand Newton’s second law of motion.  (eScience Experiment 2, Procedure 1)
  • In the final part of the lab you will create a balloon-powered vehicle to elucidate Newton’s third law of motion.  (eScience Experiment 4)

Note: Record all of your data in the tables that are provided in this document.

Take detailed notes as you perform the experiment and fill out the sections below.  This document serves as your lab report.  Please include detailed descriptions of your experimental methods and observations.

Experiment Tips

Newton’s First Law – Water in a Bowl

·  I recommend that you perform this experiment outdoors as there most likely will be some spillage of water.

Newton’s Second Law – The Atwood Machine

·  Prior to determining the mass of the washers, make sure to zero your spring scale.  To zero your spring scale, hold it vertically with no mass attach and turn the top screw until the scale reads 0 grams.  Refer to the following picture:

Turn this screw to zero the spring scale.


[img width=”189″ height=”255″ src=”file:///C:/Users/srarin/AppData/Local/Temp/msohtmlclip1/01/clip_image004.jpg” alt=”Description: SpringScale” v_shapes=”Picture 4″>

·  You may want to use the hooks on the pulley to hang your Atwood machine.  I placed mine on a hanger:

[img width=”301″ height=”226″ src=”file:///C:/Users/srarin/AppData/Local/Temp/msohtmlclip1/01/clip_image006.jpg” alt=”Description: Atwood” v_shapes=”Picture 3″>

Newton’s Third Law – Balloon-Powered Vehicle

·  Here is a picture of my balloon-powered vehicle:

[img width=”287″ height=”211″ src=”file:///C:/Users/srarin/AppData/Local/Temp/msohtmlclip1/01/clip_image008.jpg” alt=”Description: Balloon” v_shapes=”Picture 2″>

·  To add mass, I taped washers to the straw.





Material and Methods


Data table for the Atwood Machine experiment (Experiment 2, Procedure 1):

Height = __ meters

Mass of 15 washers = __ grams

Mass of 1 washer = __ grams

M1 = __ grams (lighter mass)

M2 = __ grams (heavier mass)

Trial Number

Fall time (sec)

Calculated acceleration (m/s2)












Standard Deviation

Analysis and Discussion

Water Bowl

Atwood Machine

Note: Make sure to show your calculation for the acceleration.

Balloon-Powered Vehicle

Based on your experimental results, please answer the following questions:

Water Bowl

Explain how your observations of the water demonstrate Newton’s law of inertia.

Draw a free body diagram of your containers of water from the situation in Step 3d (After walking in a straight line at constant speed, stop abruptly). In your free body diagram, draw arrows for the force of gravity, the normal force (your hand pushing up on the container), and the stopping force (your hand decelerating the container as you stop.) What is the direction of the water’s acceleration?

Describe two instances where you feel inertial forces in a car.

Atwood Machine

Draw a FBD for M1 and M2 in your Atwood machine.  Draw force arrows for the force due to gravity acting on both masses and the force of tension

[img width=”267″ height=”356″ src=”file:///C:/Users/srarin/AppData/Local/Temp/msohtmlclip1/01/clip_image009.jpg” alt=”Description: Atwood_Machine” v_shapes=”Picture 1″>

Use Newton’s Second Law to write an equation for each mass of the Atwood machine.  Solve these two equations for the acceleration of the system.

Using the masses M1 and M2, use the above expression to calculate the acceleration of the system.  How does this value compare to your experimentally measured acceleration?  What factors may cause discrepancies between the two values?

Balloon-Powered Vehicle

Explain what caused the balloon to move in terms of Newton’s Third Law.

What is the force pair in this experiment? Draw a free body diagram to represent the (unbalanced) forces on the balloon/straw combination.

Add some mass to the system by taping some metal washers to the guide straw and repeat the experiment. How does this change the motion of the assembly? How does this change the free body diagram?



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