Lab: Newton s Second Law

Transcription

1 Ph4_ConstMass2ndLawLab Page 1 of 9 Lab: Newton s Second Law Constant Mass Equipment Needed Qty Equipment Needed Qty 1 Mass and Hanger Set (ME-8967) 1 Motion Sensor (CI-6742) 1 String (SE-8050) 1 m Balance (SE-8723) 1 Super Pulley w/ Clamp (ME-9448A) 1 Dynamics Cart (inc. w/ Track) m Track System (ME-9435A) 1 What Do You Think? The purpose of this activity is to study Newton s Second Law. Using Newton s Second Law, what happens to an object s acceleration if the force applied to the object is increased but the object s mass remains constant? Background Newton described the relationship between acceleration, force, and mass as follows: The acceleration of an object is directly proportional to and in the same direction as the net force, and inversely proportional to the mass of the object: a F net m a is acceleration, Fnet is net force, and m is mass. Equation 1 Applying Newton s Second Law to the static setup used in this activity for an object accelerated by the weight of a hanging mass, neglecting friction, the acceleration of the object and hanging mass can be written as: a F net m m hangi ng g m object m hangi ng Equation 2 SAFETY REMINDER Do not let the cart run away from the user. Catch the cart before the cart crashes into the bumper or travels off the table. Follow directions for using equipment.

2 Ph4_ConstMass2ndLawLab Page 2 of 9 For You To Do For this activity, use a Motion Sensor to measure the motion of a cart that is pulled by string attached to a hanging mass that is suspended over a pulley. Next, use Capstone to plot and analyze the data. Motion Sensor PART I: Computer Setup 1. Connect the sparklink interface to the computer, turn on the interface, and turn on the computer. 2. Connect the Motion Sensor s plugs to Digital Channels 1 on the interface. 3. Launch the Capstone application on your computer. 4. Select Create an Experiment from the initialization menu. 5. Scroll down the list of alphabetized sensors until you find the Motion Sensor and double click on it. 6. Double check the actual motion sensor connections to the interface box and make sure they match the yellow and black connections on the computer screen. 7. Drag the velocity icon from the Data window in the upper left side of the screen to a graph under the Displays window. PART II: Sensor Calibration and Equipment Setup You do not need to calibrate the Motion Sensor. 1) Place the Dynamics Track on a horizontal surface. Level the Dynamics Track by placing the Dynamics Cart on the Dynamics Track. If the cart rolls one way or the other, use the Adjustable Feet at one end of the Dynamics Track to raise or lower that end until the Dynamics Track is level and the cart does not roll one way or the other. 2) Attach a pulley to the right end of the Dynamics Track. Place the Motion Sensor at the left end of the track.

3 Ph4_ConstMass2ndLawLab Page 3 of 9 3) Select three 20g masses and one 10g mass and place them in the tray of the cart being careful to not allow them to interfere with the string attached to the cart. 4) Carefully measure and record the total mass of the cart in the Lab Report section. 5) Place the cart on the Dynamics Track. The cart will be pulled away from the sensor. The cart must remain a minimum distance of 20 cm away from the motion sensor during all trials. 20 cm min 6) Use a string that is 5 cm longer than the length needed to reach the floor when the cart is next to the pulley. Attach one end to the cart. 7) Attach the mass hanger to the end of the string and record the mass of the empty hanger on the data table. 8) Conduct your first trial run with the empty hanger on the end of the string a) Pull the cart toward the left end of the Dynamics Track but keep the cart at least the minimum distance from the Motion Sensor. Do not let the mass hanger bump into the pulley. b) Start recording data and then release the cart. c) Stop data recording before the cart reaches the pulley. d) Stop the cart before it collides with the pulley. e) Repeat steps 1-5 for three repeat trials. 9) Analyze the Data using the graph a) Click and drag the cursor to draw a rectangle around the region of the velocity vs. time plot that shows the movement of the cart. Result: The area will be highlighted.

4 Ph4_ConstMass2ndLawLab Page 4 of 9 b) Select the Linear curve fit by clicking the Fit menu button ( ). Select Linear. The slope of the velocity vs. time plot is the average acceleration of the cart. c) Record the slope of the linear fit as acceleration in the Data Table in the Lab Report section. d) Using the measured mass values, calculate and record the theoretical acceleration of the system in the Lab Report section. 10) Take a 10 g mass from the tray of the cart and place it on the mass hanger at the end of the string and repeat the steps of the data recording section. 11) Continue to increase the mass on the hanger by 10 grams at a time and repeat the data recording steps until all of the masses in the cart are at the end of the string.

5 Ph4_ConstMass2ndLawLab Page 5 of 9 PART III: Data Recording Record your results in the Lab Report section. Lab Report - Activity P08: Newton's Second Law Constant Mass What Do You Think? Using Newton s Second Law, what happens to an object s acceleration if the force applied to the object is increased but the object s mass remains constant? Data Table Total System Mass Cart + all masses (kg) Hanging from Mass (kg) v-t graph slope ************* Trial 1 Trial 2 Trial 3

6 Ph4_ConstMass2ndLawLab Page 6 of 9 Hanging Mass (kg) Average (Exp. slope of v-t graph) Theoretical (Equation 2) Theoretical Force (Fg = m g) Hanging Mass Percent Difference

7 Ph4_ConstMass2ndLawLab Page 7 of 9 Questions 1. What is the percentage difference between the measured and calculated values of acceleration? Show work for one calculation. Remember, % difference measured theoretical theoretical 100% 3. What are some possible reasons for any differences between the measured and calculated or theoretical values? 4. Plot a graph of Force vs. and plot the best fit line of the graph. Calculate the slope of the best fit line. Show work for slope calculation. 5. What is the physical significance of the slope of the graph in #4

8 Ph4_ConstMass2ndLawLab Page 8 of 9 6. Discuss how well the value of the slope agrees with what you would expect and discuss some possible reasons why it may not agree.

9 Ph4_ConstMass2ndLawLab Page 9 of 9 Extra Credit Extension: In this lab you varied the force acting on a cart system while keeping the mass constant. Repeat the experiment you performed using a constant force and varying the mass. Do this for 3 different values of mass and compare the differences between theoretical and experimental acceleration values. Total system mass = Cart + all masses Total hanging mass Theoretical force from Total Hanging Mass (Fg = m g) Total System Mass from v-t graph slope ************* Trial 1 Trial 2 Trial 3 Hanging Mass Average (Exp. slope of v-t graph) Theoretical (Equation 2) Theoretical Force (Fg = m g) Total System Mass Percent Difference