Lab 04 - Second Law of Motion

Lab 4: Second Law of Motion Name: _______________________________ _ In this lab we are going to explore the second law of motion using a system of two masses: one resting on top of a horizontal table and a hanging mass connected to the first through a pulley. Second Law of Motion 1. Please click on the following link to access the browser-based simulation we need to do this lab activity: http://www.thephysicsaviary.com/Physics/Programs/Labs/NewtonsLawPhotogateLab/ 2. Click on “Begin”. Click on “Masses” button on the upper right of the screen. Make sure that the mass of the hover puck, m p , is 900 g; if it is not, change it until it is 900 g. Change the hanging mass, m h , to 20 g. Click on the “Return” button. 3. Click on the green button at the center of the screen. Click the “Start” button on the upper right of the screen. After the hover puck reaches the right side of the table and comes to a stop, click on the red button at the center of the screen. Your screen should now look like this: In this lab we will refer to the times in the data table that appears on the screen by the number of the row. For example, in the figure above, t 1 = 38.4928 s, t 2 = 39.2326 s, and so on. AGB_DallasCollege

Lab 4: Second Law of Motion 4. Calculate the interval of time Δt 1 it took the hover puck to pass through gate 1 by subtracting t 2 – t 1 , which in the figure above is: Δt 1 = 39.2326 s – 38.4928 s = 0.7398 s. Write Δt 1 in Table 1. Calculate the average velocity of the puck at gate 1 (v 1 ) by dividing the length of the card on top of the hover puck, L (0.234 m in the previous figure), by the interval of time Δt 1 : v 1 = L/Δt 1 . Write v 1 in Table 1. 5. Calculate the interval of time Δt 2 it took the hover puck to pass through gate 2 by subtracting t 4 – t 3 , which in the figure above is: Δt 2 = 40.4392 s – 40.0494 s = 0.3898 s. Write Δt 2 in Table 1. Calculate the average velocity of the puck at gate 2 (v 2 ) by dividing the length of the card on top of the hover puck (L) by the interval of time Δt 2 : v 2 = L/Δt 2 . Write v 2 in Table 1. 6. Calculate the average experimental acceleration a e for this hanging mass using the formula: a e = (v 2 – v 1 )/(t 4 – t 2 ), and write it in Table 1. Please do NOT be confused with the subscripts of the times and the subscripts of the time intervals and velocities. As described in the preceding steps, the subscripts on the time intervals and velocities refer to the gates, and the subscripts on the times refer to the rows in the data table on the screen. 7. Calculate the theoretical acceleration of the system by using the formula a t = m h g /( m p + m h ), where g = 9.81 m/s 2 . Write a t in Table 1. Calculate the percent of error of a e relative to a t using the formula % error = (|a e – a t |/a t ) x 100 and write it in Table 1. 8. Click on the “Reset” button. Click on the “Masses” button. Increase the hanging mass to the next available value. Click on the “Return” button. 9. Click on the green button at the center of the screen. Click the “Start” button on the upper right of the screen. After the hover puck reaches the right side of the table and comes to a stop, click on the red button at the center of the screen. 10. Calculate the interval of time Δt 1 it took the hover puck to pass through gate and write this value in Table 1. Calculate the average velocity of the puck at gate 1 (v 1 ) by dividing the length of the card on top of the hover puck by the interval of time Δt 1 : v 1 = L/Δt 1 . Write v 1 in Table 1. 11. Calculate the interval of time Δt 2 it took the hover puck to pass through gate 2 and write this value in Table 1. Calculate the average velocity of the puck at gate 2 (v 2 ) by dividing the length of the card on top of the hover puck by the interval of time Δt 2 : v 2 = L/Δt 2 . Write v 2 in Table 1. 12. Calculate the average experimental acceleration a e for this hanging mass using the formula: a = (v 2 – v 1 )/(t 4 – t 2 ), and write it in Table 1. Calculate the theoretical acceleration a t for the system and write it in Table 1. Calculate the percent of error of a e relative to a t and write it in Table 1. 13. Repeat steps 8 to 12 until Table 1 is completed. AGB_DallasCollege

Lab 4: Second Law of Motion Questions 1 . The formula for the theoretical acceleration, a t = m h g /( m p + m h ), is the result of the application of the second law of motion to the system composed of the hover puck and the hanging mass: Σ F = m h g = (m p + m h ) a t . Why is the weight of the hanging mass the only force responsible for accelerating the system? 2 . Let’s assume that the acceleration of the 900-g hover puck, when pulled by a 150-g hanging mass, is 1.40 m/s 2 without friction. If there was a kinetic friction force of magnitude 0.120 N acting on the hover puck, (a) Calculate the net force acting on the system while it is moving. Include the steps . (b) Calculate the acceleration of the system. Include the steps . (c) what is the coefficient of kinetic friction µ k between the hover puck and the table? Include the steps . AGB_DallasCollege

Lab 4: Second Law of Motion AGB_DallasCollege