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Transcript
DSHS AP1 Physics Mathy Ch 4 Forces Lab #5 Atwood Demonstrator Do not write on this document Uniformly Accelerated Motion: The Atwood Machine Newton's first law of motion states that objects at rest remain at rest unless an unbalanced force is applied. The second law of motion describes what happens if the resultant force is different from zero. If the acceleration is constant, the body is said to be moving with uniformly accelerated motion. The purpose of this experiment is to measure the acceleration of a given mass produced by a given force and compare it with that calculated from Newton's second law of motion. The Atwood machine consists of two weights connected by a light, flexible string which passes over a light pulley. The pulley should be nearly frictionless. The machine is used to measure the acceleration produced by an arbitrarily chosen force acting on a given mass. Using F = ma, the acceleration can be determined. Materials Base stand Small Radius Pulley String Stopwatch Hooked masses Equations F applied = ma (m2-m1)g = (m1+ m2) a + f a= 2x / t2 y Procedures 1. Make sure you have at least 1.25m of string. Your masses must eventually touch the lab floor. 2. Using a total mass of 1000 g, put 500g on one side and put 500g ( 400g with five 20g masses) on the other side. Determine the force of friction in the machine by transferring masses from the ascending side to the descending side until the mass on the descending side moves downward with uniform velocity when given a very slight push. Record the mass on the descending side, the mass on the ascending side, and the force of friction. Don’t forget…. Arrange the masses so as to have five 20-gram masses on the ascending side when the machine is in the balanced condition. 3. Transfer one 20g mass from the ascending side to the descending, and thus determine the acceleration produced by the net force. Begin the observations when the ascending mass is on the floor, starting the stop watch at the instant when you let the weights go, and stopping it at the instant when the other mass strikes the floor. Record four independent observations. 4. Measure the traversed distance. 5. Repeat procedure (3) using accelerating forces of 40, 60, 80, and 100 grams by transferring additional masses each time. Make four independent observations for each accelerating force. Data Suggested Data Tables Descending mass Ascending mass m1+m2=_____________kg m2-m1(kg) 1 2 x=____________m Time 3 4 Average time Calculated Friction Force=____________ Applied Force (m1-m2)g (N) Experimental Acceleration (m/s2) Theoretical Acceleration (m/s2) % of error Calculations 1. Compute the average time taken with each accelerating force. 2. From the known distance and time taken in each case, compute the acceleration of the system caused by the mass differences for each Trial 3. Calculate the applied force (m2-m1)g for each mass difference and record in the data table. Use 9.81m/s 2 for g. 4. Compute the theoretical value for the acceleration from Newton's second law of motion (via Atwoods equation). Assuming this to be the correct value, compute the percent error of the observed value for each case. Questions for Discussion 1. Plot a graph of your experiments Applied Force vs acceleration . What does the slope represent? Describe the relationship between force and acceleration observed in this experiment. 2. According to Atwood’s equation, the applied force (m2-m1)g should be proportional to acceleration a with the total masses m1+m1 as the constant and frictional force f as the intercept. According to your graph’s linear regression equation : find the slope of your graph and discuss what it should have equalled and discuss the y intercept and what it should have been. 3. Derive the Atwood equation and show its application to this lab! Conclusion