Newton S 2Nd Law Lab

Name ______Lab Partner______

Newton’s 2nd Law of Motion Lab

Purpose - To verify that Newton’s 2nd Law of Motion, F=ma, is valid through two methods by:

 graphing net force (Fhanging) versus acceleration (afrom tape) for a constant mass and comparing the slope to the total mass used.

 comparing the acceleration found on the tape to the acceleration calculated using Fhanging=mtotala

Testable Question: What is the relationship between Force and Acceleration when mass is held constant?

Discussion - Explain what Newton’s 2nd Law of Motion says below. ______What variable would the slope of a force F (y-axis) versus acceleration a (x-axis) graph give you? ______If the quantity you mention above is held constant, what shape should your line-of-best-fit slope have? ______Why?______

Hypothsis: If: ______Then: ______

Materials – 7 meters of ticker tape, meter stick, ticker timer, pulley wheel, 2 C-clamps, tape, cart, 1 meter or string, set of masses (50g, 100g, two 200g, 500g)

Procedure: . Set up equipment as shown in diagram on the next page. . Find the mass of the cart and convert mass in grams to kilograms . Record the total mass of the weights you will be using in and out of the cart . Place weights in cart, then remove one of the weights (at least 200g) and hang it from pulley string to act as the accelerating force. . Why can we say that the total mass never changes for this experiment? ______. Remove various combinations of weights from the cart and hang them from the pulley to act as the accelerating force (F), leaving the rest of the weights in the car to keep the total mass (m) constant. . Run 7 ticker tapes through the timer with 7 different combinations of weights hanging from the pulley, starting with the 200 grams and increasing the hanging mass by 50 grams each time up to 500 grams . Label each tape with the accelerating (hanging) mass amount, and circle the start and end dots . Measure the total distance between the first and last clear dots on each tape that still show increasing spacing between them . count the spaces between the dots on each tape to find the total time for the run . What amount of time does each space on the ticker tape represent? ______2 . Use the time measurements and the equation d = vot + ½ at to find the accelerations for each tape. . Plot a graph of force F (y-axis) versus acceleration a (x-axis) . IMPORTANT! One lab partner should display all the group’s labeled tapes fastened neatly on a sheet of paper so that they are easily viewable.

ticker timer remaining weights to hang pulley wheel

Ticker tape cart Hanging mass taken from cart

Data: 7 tapes should be labeled with hanging mass used, start and finish dots circled, and fastened in an easily viewable display manner on a sheet of paper attached to that member’s lab. ALL group members get that data tape grade.

Calculations:

Quantity Formula used Substitution Answer w/Units

mg m kg grams/1000

Accelerating F F = mhanging g Total time #spaces x 1/60sec

dcm dm Centimeters/100 2 Acceleration a d = vo t + ½ at From tape

Acceleration from Fhanging =mtotal a hanging weight and total mass

Slope of graph slope = (F2-F1) (a2-a1) % Difference of a from tape and a from Fhanging =mtotal a % Difference of slope and total mass Graph: . The graph of Force (y-axis) versus acceleration (x-axis) should be done on graph paper only, and fastened securely and neatly to your lab writeup. . Points should be clearly plotted and a line of best fit drawn (don’t connect the dots) . The points used for calculating the slope should be clearly indicated on the line of best fit by circling them and marking them with the notations of (a1, F1) and (a2, F2). These points will not necessarily be ones that were actually plotted, as they need to be found on your line of best fit . The points you choose on your line of best fit will be the ones you show in your sample calculation table.

Analysis: List three possible reasons why the acceleration from your ticker tape differed from the acceleration you found by using the actual accelerating force divided by total mass.

1. ______2. ______3. ______

Pick one of the reasons you give above and show how changing it by a reasonable amount to compensate for the error would affect your percent difference. Show your comparison of before and after calculations below.

Source of error chosen for analysis: ______

Calculations of a Before Calculations of a After Questions:

1. In general, how did your values for acceleration found using the tape compare to the values for acceleration found by dividing the hanging mass weight by the total mass in and out of the cart?

2. What possible reason/s might there be for the discrepancy between the value for the mass you found using the graph slope and the actual total mass? ______

Demonstrate the effect of this error source on your % difference for the total mass value.

3. How might you go about finding out how much friction is present between the table top and the wheels of the cart?

4. Discuss two ways that this lab proved the validity of Newton’s 2nd law of motion.