Why can’t you calculate Work (only Torque) when pushing down on your bicycle pedals as your bicycle moves forward?
In: 7
It just has to do with how we name things in physics.
Work is a measurement of force and motion in a straight line while torque is the measurement of force around a point of rotation. Work also requires that the mass is actually moving while torque only requires that a force is being applied perpendicular to a point of rotation.
If for some odd reason you had a bike in which the pedals only moved up and down and not around a point of rotation then you could measure work rather than torque.
You can calculate the work that is done.
Work = torque * angualr displacement, just like work = force * distance for linear motion.
Let’s look at a torque of 50 Nm during 40 rotations. The angular displacement needs to be in radians so it is 40*2*pi
The work is 50 * 40 * 2 * pi =12567 joules.
This assumes the force you press with is constant, in practice it is not when you pedal a bike. You can use average force if you do integer rotation. Even for not integers, it will be close for multiple rotations
You can just use the force you press down on the pedal too. The circumference of a circle is 2 * pi. You can also say the move distance is angular displacement * radius
Torque is force * radius so if you have the torque the radius is already multiple to the force.
So torque is a way to have the radius you apply the force.
Work is only done if it is moving so if you push down and the bike does not move there is no work done. The same is the case for linear motion, push a heavy box and if it does not move no work is done.
There are pedals that are power meters. Dedicated amateurs and some pros use them.
https://www.bikeradar.com/advice/buyers-guides/best-power-meters/
You can.
Bicycle power meters do this; they have strain gauges in the crank arms, the pedals, or the rear hub. The measure the torque throughout the rotation, they know how much rotation there is, and from that they can figure out the work. They normally report in in kJ
Latest Answers