Introduction

Students in statics often struggle to connect what they are learning to what they see outside of the classroom. The activity described in this card asks students to apply statics concepts to a pair of garden clippers. In doing this, they will explore how engineering mechanics is used in household products, with the ultimate of increasing the student’s curiosity about the world around them.

Activity

Placement in course

This activity is best suited in the frames and machines section of a statics course. Students will need to sketch free body diagrams of an object containing multiple members, including two force members and multi-force members. They will also need to include support reactions from pin and slot structural supports.

Supplies and Set Up

To prepare, a set Fiskars brand garden loppers with a “Power Lever” and a measuring tape were placed on the front table of the classroom.

For displaying their work, each student group will need a large sticky note and appropriately sized markers.

Assignment

Students were told that at the store, this set of clippers cost 12 dollars more than the equivalent Fiskars set without the “Power Lever” and asked the simple question: Are the clippers with the “Power Lever” worth the extra cost?

Next, students work in pairs to analyze how a force applied to the handles is transformed into a force applied to the branch being cut. To do this analysis, students will need to recognize that the set of clippers consists of three members and draw free body diagrams (FBD) of all members, being sure to include the appropriate support reactions and measuring the clippers to determine the geometry. While drawing the FBD, they will choose where and how much force is applied to handles. Finally, they will apply the equations of equilibrium to solve for the unknown forces in each member until they are able to solve for force applied to the branch in the cutting area of the clippers.

Then the students should repeat this process to analyze with a pair of clippers without the “Power Lever”. Having completed both sets of analysis, they can make a conclusion about if the set of clippers with the “Power Lever” was worth the cost.

Display and Discussion

After completing both analyses, students will display their work on large sticky notes that can be posted around the room. Then everyone can walk around the room to see all the other groups’ work and consider the following discussion points:

• How many groups decided that the set of clippers with the “Power Lever” was worth the cost?
• How did the clippers with “Power Lever” transform the applied force?
• How did the clippers without the “Power Lever” transform the applied force?
• Did changing the position of the applied force affect the analysis?

The discussion can be conducted with the whole group, in small groups, or individually.