1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to: compute Watts and Calories for for a bicycle, up a hill

  1. Aug 23, 2009 #1
    At 6'5", 300 lbs. and old as dirt, I am a walking and rolling testimate to F=ma. This part of my project is difficult for me, because I have never taken a physics class. All the examples I have in books and PF, deal mostly with force moving down a hill. I am trying to compute Watts and Calories, while riding at any measured angle.

    I am using a BS2p basic stamp reading an 2 axis accelerometer, 2 hall sensors and a gear tooth sensor. A math coprocessor handles the math. With my current set-up the BS2p determines what gear I am in, at any time, or if I am coasting. Every calculation is started after the front wheel completes a rotation, but I have no idea if it is accurate.

    Watts = ma*gr*pcl*s*sin(theta) + Rr (so long as theta is never zero) If theta = 0, then Watts = ma*gr*pcl + Rr

    Calories = watts*0.2388459


    m = Mass = 145kg
    a = Pedal Speed = 22pi/9 rad/sec
    gr = Gear Ratio = 44 : 18 (2.44 to 1) (This is gear ratio I use the most)
    pcl = Pedal Crank Length = .175m
    s = Front tire circumference = 2.2m
    Rr = Rolling Resistance ??

    I left gravity out, because I felt it would be part of Rolling resistance. Once the initial equation is working I figured on gathering Rr by comparing computed and measured data

    thanks

    Bill M.
     
    Last edited: Aug 23, 2009
  2. jcsd
  3. Aug 23, 2009 #2

    Born2bwire

    User Avatar
    Science Advisor
    Gold Member

    There isn't a conversion between Calories and watts. Watts is power, Calories are energy. You want to know a rough estimate of how many Calories you burn going up a hill? Just find the potential energy from the change in height: m*g*h. This will be in joules though so you will have to convert to Calories which is 4184 J/Cal. So:

    145 kg * 9.806 m/s^2 * h (m) / 4184 J/Cal = 0.34 Cal/m * h (m)

    This value is going to be less than your actual work done due to the losses in the system, but it could be used as a sanity check for the equations that you have been trying to work with.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How to: compute Watts and Calories for for a bicycle, up a hill
  1. Bicycle down hill (Replies: 2)

  2. Watt is it? (Replies: 1)

Loading...