Lab 4 Kinematics in One-Dimension

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Dec 6, 2023

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Title: Lab #9: Atwood’s Machine Data Acquisition Date: 26/10/2023 Laboratory Report No.: 9 Author: Report Submission Date: Camosun College Physics 104 Laboratory Report Objective: To verify Newton’s Second Law using the Atwood Pulley System Theory: Atwood's Machine The Atwood's Machine is an apparatus consisting of two masses, m 1 and m 2, connected by a lightweight string passing over a pulley with negligible inertia. Applying Newton's Second Law: 1. The net force on m 1 is: − ft + m 1 g = m 1 a 2. The net force on m 2 is: − ft + m 2 g = − m 2 a Where: ft represents the tension in the string. g denotes the acceleration due to gravity. a is the acceleration of the masses. From these equations, we derive: The system's acceleration is: a 1 = g ( m 1- m 2) / ( m 1 + m 2) The relationship between the accelerations of the masses is: a 2 = − a 1 Plotting a 1 against ( m 1− m 2) yields a straight line, where the slope is related to gravity as: g = slope ( m 1+ m 2) 1
Apparatus/Equipment: Pista aérea lineal, planeador, cinta de chispa, temporizador de chispa. Procedure: 1. Raise one end of the air track about 5 cm off the ground. Set the timer to go off every 0.1 seconds. 2. Attach a 2-meter long strip of paper to the air track. 3. Release the cart and start the spark timer. The sparks will leave a series of dots on the tape. After that, remove the tape for later analysis. 4. Find a dot near the beginning of the tape where the dots are about 0.5 cm apart. Label this dot as your starting point, t =0.0 s 5. Move along the tape, marking every fifth dot. Label these as t 1=0.50 s , t 2=1.00 s , t 3=1.50 s , and so on. 6. Measure the distance between the dot before and the dot after each fifth dot. Note these as Δ x 1, Δ x 2, etc. 7. Calculate the cart's average velocity for each fifth dot using the formula v =Δx/2Δt, where 2Δt =0.20s. Write down these velocities and times in a data table. 8. Create a Velocity vs. Time graph. 9. Figure out the cart's acceleration from the graph. Make sure to estimate how certain you are about this value. 10. Write down the equation that describes how velocity changes with time. Don't forget to include units for each variable. 11. Use the graph to find the cart's displacement between t =1.5s and t =3.5s. Calculate the "area" under the curve for this time interval and provide an estimate of how certain you are about this value. 12. Measure the actual distance the cart traveled in that same time frame (from t =1.5s to t =3.5s) using the tape. Compare this to what you got in step 11. 2
Data Tables: Tabla 1. Data Table Dot Time (s) Displacement (cm) Displacement Δx (m) Sparker time interval 2Δt (s) Velocity (m/s) Acceleration m/s² 1 0,50 5 0,05 0,20 0,250 2 1,00 6,4 0,064 0,20 0,320 0,14 3 1,50 8,2 0,082 0,20 0,410 0,18 4 2,00 10,3 0,103 0,20 0,515 0,21 5 2,50 12,3 0,123 0,20 0,615 0,20 6 3,00 13,9 0,139 0,20 0,695 0,16 7 3,50 15,6 0,156 0,20 0,780 0,17 8 4,00 17,3 0,173 0,20 0,865 0,17 9 4,50 18,9 0,189 0,20 0,945 0,16 10 5,00 20,5 0,205 0,20 1,025 0,16 Calculations: Δ t is constant and equal to 0.1 s for each interval, the calculation for each time interval will involve dividing the change in displacement Δ x between each pair of consecutive points by 2 Δ t = 2 * 0.1 s . = 0.20 s Velocity : Now we calculate the average velocity for each interval by dividing For t = 0.5 s, v = 0.050 / 0.20 = 0.250 m/s For t = 1.0 s, v = 0.064 / 0.20 = 0.320 m/s 3
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8. Graph 1. The velocity vs Time 9. Acceleration: Plot and Determine Acceleration: The slope is calculated as Δv/Δt. We calculate the slope using two points from the table: Initial point: (0.50 s , 0.250 m / s ) Final point: (5.00 s , 1.025 m / s ) Slope a = Δ v / Δ t = (1.025 m / s − 0.250 m / s) / (5.00 s – 0.50 s) = 0.1722 m / s ² 10. The equation for velocity as a function of time for constant acceleration is: v ( t ) = v o + at With a = 0.1722 m / and v o =0.250 m / s , the equation becomes: v ( t ) = 0.250 m / s + 0.1722 m / s ² × t 4 0.00 1.00 2.00 3.00 4.00 5.00 6.00 0.000 0.200 0.400 0.600 0.800 1.000 1.200 The Time (s) vs Velocity (m/s) Time (s) Velocity (m/s)
11. Find Displacement from the Graph The formula for acceleration a in terms of velocity v and time t is: 5
If the velocity at t = 0.5 s is v = 0.25 m / s and the velocity at t = 1.0 s is v = 0.32 m / s , then the acceleration over that time interval: a = ( 0.32 m/s – 0.25 m/s) / ( 1.0 s – 0.5 s ) = 0.07 m/s / 0.5 s = 0.14 m/s² Discussion: The experiment conducted in Laboratory #4 focused on studying the motion of a cart moving on an air track. From the gathered data, a Velocity vs. Time Graph (Graph 1) was generated, displaying a clear linear trend. This behavior is characteristic of uniformly accelerated motion, aligning with the theoretical principles discussed in the lectures. From the slope of Graph 1 , an average acceleration of 0.17 m/s² was determined. This acceleration aligns with the data presented in Table 1 . However, variations in acceleration values were noted, fluctuating between 0.14 m/s² and 0.21 m/s² throughout the experiment. Such fluctuations could be attributed to factors such as potential imperfections on the air track, misalignments of the cart, or variations in the operation of the spark timer. A significant point of interest was the displacement of the cart between t=1.5s and t=3.5s. Using the trapezoid formula to compute the displacement, a value of 1.361 m was derived. However, when directly measuring from the spark tape, a displacement of 1.36 m was recorded. Despite the minimal difference of 0.001 m between these values, it underscores the precision of the technique and the importance of employing diverse methods for result verification. The velocity relationship was described by the equation v ( t ) = 0.250 m / s + 0.1722 m / × t , emphasizing how velocity varies over time under constant acceleration. In kinematic theory, it is said that an object should start from rest, but in reality, this rarely happens. In Table 1 , an initial velocity of 0.250 m/s is observed for the cart, 6
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suggesting that it already had some momentum before measurements began, possibly due to an initial push or another source of motion Conclusion: 1. The velocity versus time graph provided a clear visualization of the object's dynamic behavior over time. 2. By deriving the acceleration from the graph, we were able to accurately quantify how the object's velocity changed over time. 3. Determining the displacement using the trapezoid rule allowed us to understand the total distance the object traveled during the experiment. 7
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