Rolling friction and work done

[lezard1]

Homework Statement

I preformed a experiment to find the joules of work taken for my elastic band car to travel a distance of 18.1 meters

Does my result seem correct?

 

[denverdoc]

Your pic isn't displaying.

 

[lezard1]

noticed that the second i posted, fixed now

 

[lezard1]

This is my method

Objective:
To find the coefficient of friction for a rubber band car.

Equipment:
• Rubber band car
• Ramp
• 2 rulers
• Measuring tape
• 2 Digital Cameras capable of 30 fpsExperimental procedure:

1. Create a ramp and where it hits the ground mark off 10 cm distance straight ahead.
2. At the end of the 10 cm mark, mark 1 meter then another 10 cm.

3. Set the cameras up so each one records a 10 cm marked segment at 30 fps
4. Release the car from various heights (adjust the ramp)
5. Analyze the video to determine the average speed of the car at the beginning of the horizontal motion and at the end of the horizontal motion.
6. Record data in chart as below for each run.

Observations
Calculations
1. Using the equation V2^2 = V1^2 + 2ad; solve for the acceleration of the car.
2. Since F = ma = umg, the mass is not a factor and u = a/g.

 

[denverdoc]

This looks pretty reasonable--the math is sound,what are the rubberbands for?

 

[lezard1]

you mean the strength? they are staples #33 , the small normal ones or maybe slightly thinner.
I used a light flywheel design car that went 18.1 meters but moved slowly, the rubber band was wrapped around the axle

 

[lezard1]

what worried me was the varying values for the coefficient of friction, this was all with the same car and that value shouldn't change, I couldn't find where i went wrong in the math and repeated tests came out at close to the same exact values

 

[denverdoc]

No i wondered whether the rubber bands contribute to propulsion. If so it may explain some of the variation in the data. The rubber band would need to be slack at both measurement intervals, otherwise you are complicating this problem needlessly.

 

[lezard1]

oh, yes of course for the 18.1 m run it used elastic propulsion but for the lab trials it used a ramp(and the elastic unattached)

 

[denverdoc]

Ok good. Hey welcome to real science. If you have more than 20% variation in the data, that would be odd. I help with the pinewood derby races at the scouts--basically what you are talking about. The results can be very close and astonishingly repeatable on a good track--so let's revise that number to 5% or less.I think you have rounded your calcs off but otherwise seem reasonable--two at 0.01, and one at .00 (which can't be!).

 

[lezard1]

yes i used excel to round

 

[lezard1]

which means that although the values show rounded they are calculated to many many decimal points, so only the results are rounded, no rounding during the calculations

 

[lezard1]

thank you for the reassurance and guidance

 

[ideasrule]

Can you collect more data for different ramp heights? It seems that the higher the ramp, the greater the deceleration. This may be due to air resistance or other forms of friction which are greater for higher speeds.

Also, when analyzing the video, did you count the number of frames from the time the front of the car entered to the time that it left? If you count the total number of frames the car was visible, you have to take into account the car's length.

 

[lezard1]

i made the mistake with the length of the car the first time but i deleted that data, my car is broken but ill try to get it fixed for after christmas