Torque and Equilibrium Simulation Exercise

Torque and Equilibrium Simulation Exercise

By this point you should have read the chapters in the textbook on angular motion (chapters 10 and 11) and gone through the PowerPoint I recorded.

BACKGROUND:
So far, we’ve treated angular motion as an extension of the laws of physics. That’s true, but there’s another concept hiding in here: equilibrium. Equilibrium is how physics refers to the idea of balance. When two or more forces or two or more torques are perfectly balanced, we would say that the system is in mechanical equilibrium. You’ve probably experienced this when you were younger without even realizing it: think back to when you played with your friends and/or siblings on a see-saw and how you had to adjust where you were sitting to bring the see-saw into balance. In physics speak, as gravity pulled you down, you and your friend were exerting a torque on opposite-sides of the see-saw. If you weren’t close to the same weight, you had to adjust where you sat to bring the system into equilibrium.

OBJECTIVES:
– Understand how force relates to torque.
– Explore the concept of equilibrium.
– Predict when two separate torques will be in balance.

MATERIALS
* Personal computer with internet access capable of running HTML5.

PROCEDURE
Logon and Setup – Gain access to and set up the simulation software.
1. Go to:
https://phet.colorado.edu/sims/html/balancing-act/latest/balancing-act_en.html
You should see a screen similar to this:

2. Double click on “Balance Lab” to begin the simulation. You should then see a screen similar to this:

3. Familiarize yourself with the control panel.
a. You can select “Mass Labels” to display the mass of each weight stacked on the balance beam.
b. You can select “Forces from Objects” to display the gravitational force vectors from the objects on the beam.
c. You can select “Level” to display a visual reminder of when the beam is perfectly level.
d. The balance beam is marked at .25m intervals. You can use the “Position” control panel to display make that easier to keep track of.
e. Use the slider below the balance beam to remove the supports and let the mean rotate.
f. Multiple objects can be placed on the balance beam and you can use the purple arrows to find more options. You have a choice of bricks of four different masses (unfortunately, they can not be stacked on top of each other), four people with different masses, and eight mystery objects.
g. The orange button can reset the simulation.

 
Procedure – Use the simulation software to explore the following scenarios and answer the questions.

1. Imagine an object placed on one end of the beam. What forces are acting on that object?

2. Start by placing 5kg worth of bricks 1.5m away from the pivot point. What is the torque on the beam?

3. What would happen if the bricks were moved to .25m from the pivot point? Calculate the torque and explain what you think will happen.

4. Then test it and verify your predictions. Did they match? Why or why not?

Mass Location
5kg
20kg
5. Remove the first bricks, then place 10kg of bricks so that they’re 1.5m from the pivot. Calculate where you would have to place 5kg and 20kg of bricks to balance the torques on each side of the beam. Write the results in the table below.

6. Test your predictions from the previous step. Were they accurate? If not, what would you have to bring the two sides of the beam into equilibrium?

7. Calculate where you would have to place 15kg of bricks to balance the beam. (Hint: It’s not possible to actually do balance it in the simulation.)

Mystery Object Position of Brick Position of Mystery Object Mass of Mystery Object
A
B
C
D
8. Place a 5kg brick 2m from the pivot point, then place Mystery Object A on the other side. Reposition one or both of the objects until the beam is at equilibrium. Calculate the mass of the Mystery Object, then repeat for Mystery Objects B, C, and D. Write your results in the table below.

9. Design your own experiment using the options available in the simulation. Describe phenomenon what you want to test, a brief procedure, and the results you got.

 
CONCLUSIONS:

1. How could you ensure that the system represented by the beam was in equilibrium? What could you adjust to bring the system into equilibrium?

2. When do you think these concepts would be useful? That is, think of situations where you might need to make sure that the forces and/or torques on an object are in balance.