As you hold your leg in this position, the upper leg exerts a force on the lower leg at the knee joint. What is the magnitude of this force?
If you stand on one foot while holding your other leg up behind you, your muscles apply a force to hold your leg in this raised position. We can model this situation as in (Figure 1). The leg pivots at the knee joint, and the force that holds the leg up is provided by a tendon attached to the lower leg as shown. Assume that the lower leg and the foot have a combined mass of 3.2kg, and that their combined center of gravity is at the center of the lower leg.
What is the direction of the force exerted by the upper leg on the lower leg at the knee joint?
- JeffLv 52 years ago
Torque is 'twist' whomever made the diagram needs schooled.
- Roger the MoleLv 72 years ago
You've got a third-class lever with the fulcrum at the knee joint, an upward force to be found 5.0 cm away from the fulcrum, and a downward force of 3.2 kg at 25 cm from the fulcrum.
(3.2 kg x 25 cm) / 5 cm = 16 kg
vertically upward (If there was any question, biologists can tell you muscles exert no force except by contraction.)