131 Lab Centripetal Force Mario DeLaPaz Kui Chen Phys 111A Objective : To understand that there is centripetal force acting on an object in circular motion and the acceleration is always directed radially inward. Theoretical background : 1. U=mgh 2. K = mv2 3. W=Fd 4. W=U 5. F= m(g+v2/r) Tension force at the lowest point 6. The velocity vector tangent to the circle is always perpendicular to the circle radius. Newton's law for x and y components are : in x direction, Tsin()=max ; in y direction : -mg+tcos(). The lowest point ay is just the radial acceleration v 2/r . Solving for T gives you the fifth equation. Tension T and weight mg are the only two forces visible in FBD. Mg is conservative but T is not.Aby work done by tension would change the energy of pendulum. Tension is perpendicular to velocity and Work done by the Tension force is zero. 7. Equipment L ist : 8. PC with UL I ; Force Probe ; Clamp to hold force probe ; Pendulum with different masses 9. P rocedure : 10. Connect force probe to UL I port DIN1. Open Logger Pro file. A UL I Force Probe attached to DIN1 must be calibrated before collecting data. Follow the calibration
inst ruct ions. Weigh the pendulum. Measure the pendulum length L. Hang the pendulum on the force probe. Li ft the pendulum to the horizontal posit ion. Click the Collect but ton, wait 2 seconds then drop t he pendulum and let it oscillate. The force Vs t ime is plotted. Click the Stop button and read the value of the f irst maxim um force. The force value is at maxim um when the oscillat ing weight is vert ically below the suspension point. The Newton's applied Law at t he point allows one to calculate the Tension force.Calculate the % difference between the maxim um Force from the plot and Tension calculated from equat ion 5. Measure the pendulum period. The t ime distance between the adjacent maxima is half of period. Record the data. 11. 12. 13. Data and Calculations : See page attached 14. Discussion : 1. The amplitude of force becomes smaller. What is the reason for that? 15. The reason the amplitude becomes smaller because the velocity decreases because of gravity and force goes downward. 2. When you use the conservation of energy you assume that the energy of system doesn't change but it does. Can you evaluate how much evergy was lost (%) before theh pendulum reached the first minimum.? 16. Mgh+fFD=1/2 mv
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3. What element in the equation 5 is responsible for the maximum of force getting smaller with t ime? What energy does i t represent? 17. Velocity, it represents Kenetic Energy 4. How would the plot of the Force look if the experiment were made in a vacuum? 18. There would be no gravity thus, the velocity would be constant. 5. What is a vacuum?
19. A vacuum is where t here is no gravity or air resistance. 6. What way does the air affect the pendulum mot ion? 20. The air resistance affects the mot ion by slowing it down. 21. Conclusion : 22. In this lab I learned how the force of the pendulum stayed the stayed the same as long as the mass stayed constant. I also learned to use the conservation of energy to solve for the tension. I have a full understanding of the formulas by visualizing what's happening. 23.