In our last activity, we focused on familiarizing ourselves with a few common simple machines and the accompanying calculations involved with determining the mechanical advantage provided by their use. A key component to any successful engineering design solution is to know your components intimately. This often requires characterizing the performance of key components, which leads to better overall product performance.

The mousetrap acts as the powerplant for the mousetrap car your team will design. Being able to harness and manipulate the power output is extremely important. In this activity, you will determine the applied force exerted by the “hammer” of the mousetrap lever as it makes its 180 degree overall motion. This data will play an important role in the optimization of the powertrain of your mousetrap car.

In order to optimize the transfer of energy stored in the spring of a loaded mousetrap into kinetic energy of the mousetrap car, we need to determine the avereage work that the trap is capable of doing. Recall from physics that work is defined as the product of a force applied over a distance. Symbolically this can be represented as:

W=FdWhere the work done is in Joules, the force is measured in Newtons and the distance measured in meters.

Obtain a Victor mousetrap from your instructor. Considering that the goal is to design and build a mousetrap car that travels as great of a distance as possible,

1. Identify some concerns about using the mousetrap as a power source.2. Suggest modifications to address those concerns.

State an objective for this activity in your engineering journal.

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D Activity 2: The LeverMousetrap Characterization

PWHAT DO YOU THINK? • LEARNING OBJECTIVES

P R E P A R I N G

Figure 1: A common spring-powered mousetrap

In your engineering notebook, make a table that will hold the following information for the entire range of motion of the mousetrap “hammer”: Force (N) , distance from center (cm), Angle (Θ).

In order to determine the effect of the length of the lever arm (mousetrap “hammer”) on applied force, mark the rear of the mousetrap in 0.5 cm increments, as shown in the photo at right.

Once you have marked your mousetrap, you need to create your experimental setup. The photos below illustrate the proper setup:

Zero out your vernier force sensor before proceeding. Collect a series of force measurements using the supplied vernier force sensor (set to +/- 50 N), measuring the force required to maintain the mousetrap at a certain angle starting 1 cm from the center spring, increasing the angle by 10 degrees each time until you have rotated as close to the full range of motion of the mousetrap as possible. Repeat measurements for 2, 3, and 4 cm from the center spring.

2AWork • Graph • Extrapolate

A N A L Y Z I N G

EMousetrap Characterization

E X P E R I M E N T I N G

Figure 1: Angular View of Test SetupFigure 2: Top View of Test Setup

1. Create graphs of Force vs. Angle for each of the distances (from the center spring).2. Create graphs of Force vs. Distance (traveled by lever) for each of the distances (from the center

spring). HINT: You will have to convert the angle rotated into a distance for these graphs. Remember also that the full range of motion is 180 degrees. Based upon this, you can use the following expression to determine the distance traveled by the lever:

3. Does the spring exert a constant or changing force upon the lever arm? Justify your response.4. Read the linked file on work & energy (don’t worry about the problems in the document, but rather

analyze the concepts presented). Determine the total work done by the spring upon the lever. Explain how you determined this value.

How Do I Know?Consider the following two mousetrap powered car designs (“A” and “B”) below. Using what you know from this experiment, which car is built to maximize acceleration? Justify your choice using data from this lab experiment.

Why Do I Care?Recall that your goal is to design a mousetrap car that travels as far as possible. How will you apply your findings from this lab experiment to your design goal?

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CTKnow? • Care?

C r i t i c a l T h i n k i n g

Figure 4: Mousetrap Car "A"

Figure 3: Mousetrap Car "B"