Even if not necessary it might be good to know and understand some of the basic elements in weightpulling. If you want to add something to this page or more specific information, please email info@ewpf.org.
When the weightpulling cart is loaded with weight there is a downward pointing force, we call it here the weight force. This weight force causes the force that resists to pull the cart. To exceed this resisting force dog has to pull the cart with a force that we call the pull force.
| Pull force = weight force x friction coefficient |
The needed force to pull the cart is calculated by multiplying
the weight force (total cart weight) with the the friction coefficient.The
friction coefficient is an unique coefficient for each track and cart. A typical
friction coefficient for a weightpulling track is 0.01.
Example: The cart weights 750 kg (1,650 lbs). The needed force to pull that
cart is 0.01 x 750 kg = 7.5 kg.
Good to know: The friction coefficient is always different on different tracks.
This makes it impossible to compare the results on different tracks and events.
On a poor track the coefficient varies even during the day, position and weights.
For a serious weightpuller it is very important to know that
there are two kind of frictions on the weightpulling track.
One is the starting friction (static
friction) and the other one is the dynamic friction
(kinetic friction).
The starting friction is in effect when the cart is not moving. The dynamic
friction is the one when the cart is moving. The starting friction is always
bigger than the dynamic friction. This means that it is always harder to get
the cart to move than keep it moving. This makes it essential to try keep
pull the cart in one smooth pull!
Example: One track had a dynamic friction coefficient of 0.02 and a starting
friction coefficient of 0.04. The cart weight is 600 kg. This means that the
dog has to pull in the beginning, when the cart is still not moving, with
a force of 24 kg. As soon as the cart is moving the needed force drops to
12 kg.
You can easily measure the coefficients for your own track. All you need is a scale. First weight how much the cart is weighting. Put enough weights on it. Use a fishing scale to measure how much force is needed to pull the cart. Divide the needed force with the weight of the whole cart.
A good weightpulling cart is one that always has the same friction coefficient, no matter how much weight, how much speed, what direction or part of the track.