physics lab

PHY 1401 Name____________________ LAB: Torque and the Balancing Act Objectives 1. 2. 3. 4. Describe the factors that determine whether two objects will balance each other Predict how changing the position of a mass on the balance will affect the motion of the balance Use a balance to the find the masses of unknown objects Calculate torque Materials  Computer  https://phet.colorado.edu/en/simulation/balancing-act Theory If masses are hanging on a meter-stick on both sides of the pivot-point, these masses simply act like torques. They try to rotate the meter stick. For example, in the figure above mass 1 is trying to rotate meter-stick in CCW direction and masses 2 and 3 are trying to rotate the meter-stick in the CW direction. Mass 1, 2, 3 are applying a force (torque) equal to their weight (recall F = ma or w = mg). If the meter-stick is balanced, in other words not rotating then we can say it is in rotational equilibrium. i.e. 𝛴𝜏 = 0 ⇒ 𝜏+ + 𝜏− = 0 ⇒ 𝑟1 𝐹1 sin 𝜃 = 𝑟2 𝐹2 sin 𝜃 + 𝑟3 𝐹3 sin 𝜃 (Here r is the lever arm aka moment arm or position vector, and θ is the angle between r and F. θ is 90o for all the forces in the figure above). ⇒ 𝑟1 𝑚1 = 𝑟2 𝑚2 + 𝑟3 𝑚3 is the desired equation for rotational equilibrium (since F = mg, and g gets canceled from all the terms) Procedure Develop your understanding: Explore the Intro screen, then explore to develop your own ideas about what determines how objects balance each other. Torque and Balancing Act 1 Explain your understanding: Use your own words and captured images from the simulation to show you can: 1. Make two same mass objects balance in at least two different ways (A and B). a. Explain why it makes sense that there is more than one way to make the objects balance. 2. Make two different mass objects balance in at least two different ways. a. Explain why it makes sense that there is more than one way to make the objects balance. Complete data table below for # 1A, 1B, 2A, and 2B. Test your understanding: Open the Balance Lab screen, use some different objects and masses to apply your ideas. Torque and Balancing Act 2 3. Make two same mass objects balance in at least two different ways. 4. Make two different mass objects balance in at least two different ways. Complete data table below for # 3A, 3B, 4A, and 4B. Quantify your understanding: For the above situations, calculate the counterclockwise torque, the clockwise torque, and the percentage difference between these. Step & Way Counterclockwise Torque (Nm) Clockwise Torque (Nm) Percent Difference (%) 1A 1B 2A 2B 3A 3B 4A 4B Show your work (two sets of data rows): Torque and Balancing Act 3