# Torque and Bench Press Design

In Physics 11 the concept of torque is often quite easy to calculate but, from my experience, is not something that many students fully understand.  The implications of torque are enormous in engineering but also have real world applications for our students.  Many of our students have been on a ‘teeter-totter’ and experienced the effects of leaning back to go down faster.  I would present students with the problem of a loaded bench press (4-45lbs plates a side) and ask their thoughts on how many plates I can take off one side before the bar flips.  The intention of using this example is it would relate to my students and would have them think about torque in their daily lives.

I would use the following question to guide the inquiry process:

How can we explain the gym using physics? What is the safest design of a bench press to prevent weight tipping?

The question is intentionally broad as there is no single answer to it.  We will approach it through the lens of torque (and can revisit from other angles as we see fit – pulleys etc).

 Phase of Instruction Teaching Method Student Activity Generate Relationship Show students a picture of a loaded bar with 405lbs and ask how many 45lbs plates can be removed from one side before the bar flips.  This is a complex question as the pivot point is very close to the heavier side.  Ask students what they think will happen if a smaller bench press is used and the anchor points are closer together (the pivot point would be further from the weight). Students hypothesize what is going to happen, explore bench press design, design a bench press to minimize weight tipping yet is still usable and compare their results with others in the class. Evaluate the relationship Take the class to the weight room and recreate the situation and see what happens (teacher led – be careful!) Have students complete the PhET simluation (https://phet.colorado.edu/en/simulation/balancing-act) on tourque and balance. Students test their theory with what actually happens and are given time to work with an unloaded bar (Safely!!) and see how position and pivot point effect when the bar will tip.  Students capture their experiment using their devices and explain their findings in a video journal. Modify the relationship Other implications and extensions of where these theories of physics apply are covered (structural engineering, mechanical engineering) Students modify the design of their own bench press with detailed explanations of their design choice and answer the driving question.

Any thoughts or suggestions on the design process or the guiding questions?

Baljeet

Khan, S. (2007). Model-based inquiries in chemistry. Science Education, 91(6), 877-905.

Khan, S. (2010). New pedagogies for teaching with computer simulations. Journal of Science Education and Technology, 20(3), 215-232.

1. AndrewYeung says:

Hi Baljeet,

I like the connection to using Bench Presses for experiencing torque, keeping safety in mind. I wonder whether there are virtual simulations where you can mimic the same observations to avoid the hassle of coordinating with gym class schedules, etc. To be sure, high school-ers are generally into doing gym so the application is relevant. We wouldn’t want students to purposes change the torque to throw people off balance now =)

Andrew

2. MichaelHengeveld says:

Hey Baljeet,

I like how you don’t just present the students with data, like the examples given in our readings. Your modification of T-GEM to include real data gathering allows the students to engage in that authentic, complex processes. The safety aspect is also an important motivator, especially for those students in the class who may not care about bench-pressing.

Although this extends beyond the mandate of our T-GEM assignment, do you follow your projects with any activities to highlight transfer tasks? We have been trying to do this as an informal test of how well they understand the domain. I find that students struggle to see the governing conceptual structure as pertaining to anything other than the literal example given. After a project on bridges, for example, I’ve needed to point out that a bicycle frame is governed by the same laws and ideas.

Mike

3. Jocelynn Mortlock says:

I agree with Andrew and Michael, I think this a fantastic way to have students collect data and experience Torque for themselves! Although a simulation would be nice, it would be ideal to have both the real physical application as well as the simulation to help solidify the understanding. While the physical and safety aspects help students understand the general feeling of torque, a simulation can also push the torque to extremes to allow students to safely understand the effects. Great lesson model!

Jocelynn

1. baljeet gill says:

I agree with you all about the use of simulations and I wonder if this could be something that is used to extend understanding. Similar to what Michael said about extending knowledge to other examples, in my case trusses or turbines, I think a simulation on these topics could help determine if students are able to test their knowledge in other contexts.

Baljeet

4. ChristopherRozitis says:

Hi Baljeet

I like the fact that you brought in a real world problem. It brought me back to when I worked in a local gym — over 30 years ago.

I wonder if you could take the class into the school gym and try it out. Maybe use a smaller barbell and smaller weights.

A good next step might be…I noticed you had references at the bottom of your post, however, I do not see them in the above text.

Christopher