Name: Objective: Does F = ma work for circular motion? Seriously, does it work in real-life??? We will use. 2, and. v R

Transcription

1 Centripetal Force Lab Objective: Does F = ma work for circular motion? Seriously, does it work in real-life??? We will use F ma, C C Name: HONOS v a C, and v to find out in this lab. Partners: Equipment: Centripetal force Apparatus including smooth tube, string, rubber stopper, multiple washers, scale, meter stick, and stopwatch. Procedure: Hang washers on the paper clip under the tube. Measure the radius of the circular motion. Measure the mass the paper clip and the washers. Swing the stopper around in a horizontal circle, keeping the radius constant. he radius of your circle should be approximately cm long. Make sure that the paper clip does not touch the bottom of the tube, and also that it does not fall during the run. (Use your shoulder, not your wrist, to swing the stopper). After you have gotten the stopper circling your head, find the period by timing 10 revolutions. Make sure to start your timing on ZEO, NO ONE, and end at ten. Add more washers, find your new mass, and then repeat. Do runs for,,,,,, & washers. Data: Data able: F C m Force pulling in on the object during Circular M otion Massof the object in Circular M otion adius of the Circular M otion Period of the Circular M otion # of Washers Mass of clips & washers (kg) FC (N) Mass of stopper, m (kg) adius (m) (sec) (1/s )

2 Pre-Analysis: mv In the space below, take FC and and combine them together tohave a formula for FC that v contains only thevariables m,,and (as well as a constant and ). Makesure to show your work. Analysis: 1. On the grid below, make a graph with FC on the y-axis (vertical) and 1/ on the x-axis (horizontal). FC. 1/

3 4m. emember that FC is really just F = ma in disguise. In order to prove that this equation 1 works for circular motion in the real world, we will need to use our data to show that F. 1 From the plotted data on the previous page, is FC? emember, the symbol means proportional to. Explain how you know (yes or no)? 4m 1 3. We can re-write the equation FC as F 4 0 C m. It is now in the form of a line, or y = mx + b. Notice that the slope of the line should be 4m and the y-intercept should be zero. a) Is your y-intercept close to zero? Yes or no? If not, an explanation is needed. b) Calculate the slope of your graph. (we will call this slopeactual ) c) Compute the value of 4m. (we will call this slopetheoretical ) d) Is the slope of your graph close to 4m? Yes or no? If not, an explanation is needed. 4m 4. Again, if your data truly validates FC, then the slope of your graph should be close to 4m. Find your percent error using the equation below. Percent Error = slope actual slope theoretical slope theoretical 100% = = %

4 Conclusions 5. Explain 4 different ways that error could have crept into your lab. Be both specific and insightful. A lack of thoughtfulness will result in a loss of credit. DO NO include the fact that the problem was actually a CONICAL PENDULUM. his will be discussed in the next part of the lab. a) b) c) d) 6. What were you trying to prove in this lab? Was your lab successful? Explain. 7. If the answer to question #6 above was no, explain what happened and what you could do better if you repeated this lab. If your answer to question #6 above was yes, you may skip this part

5 PA II NOW, let s assume that your percent error in part I of this lab was due entirely to the fact that the string wasn t flat. In other words, since the swinging mass on a string was really a conical pendulum, treating it like a flat, horizontal circle problem was a simplification of the real problem that led to a percent error. herefore, in this part of the lab, we will calculate what the swinging angle was for each of the 4 trials we did in part 1 of the lab. In the space provided, show how the equations,, and v= can be combined to form a single equation that uses, g,, and fully simplified, and write it on the line below. to solve for. Make sure the equation is = Complete the table below for each of your 4 trials. rial # of washers Average Period (sec) String length (m) Conical Pendulum angle (deg) Questions and Calculations Do you see a trend with the conical pendulum angles for the 4 trials? You should. Why does this trend make sense? Explain.

6 Explain what should happen to the angle as the mass at the end of the string continues to increase by completing the sentence below. If the hanging mass increases and approaches infinity, then the angle (between the string and the vertical) approaches. In a physics classroom not so far away, a student performs the same lab that you just completed. He thinks he is pretty hot stuff and ends up with zero percent error, claiming that he was spinning the mass so fast that the string (attached to the stopper) was perfectly parallel, and that his lab was NO a conical pendulum. Explain why he cannot be correct, using the concept of EQUILIBIUM.