Finding the force of the femur on the knee cap.

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In summary, the conversation discusses a simplified model of the leg, with the femur, tibia, and quadriceps muscle playing key roles. It then poses a question regarding the force of the femur on the kneecap, given the force applied by the muscle to the tendon. The solution involves calculating the x and y components of the force, resulting in a final answer of 191.4N for the x component and -1.67N for the y component. A larger image and corresponding equations can be viewed in the provided link.
  • #1
meaganl
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Homework Statement



The diagram of the leg shows the femur (1) and tibia (2). The quadriceps muscle (3) applies a force to the lower leg via a tendon (4) that is embedded with the kneecap (5). If the force applied by the muscle to the tendon is FM = 420 N, what is the force of the femur on the kneecap? A simplified model of the leg is shown next to the diagram. The leg bones are represented by two beams attached by a pin. The tendon is modeled by a rope and the kneecap acts like a pulley. The tendon above the kneecap makes an angle θ1 = 23° with respect to the vertical, and the portion of the tendon below the kneecap makes an angle of θ2 = 24° with respect to the vertical. Enter the x component, followed by the y component.

https://www.physicsforums.com/attachment.php?attachmentid=51494&thumb=1&d=1349314642

Homework Equations



fnet=ma



The Attempt at a Solution



I tried:

Fnetx=max
T1x + T2x + Ffemurx = 0
-240sin23 + -240sin24 + Ffemurx= 0
-93.78 -97.62 + Ffemurx=0
Ffemurx= 191.4N

Fnety=may
T1y + T2y + Ffemury=0
240cos23 -240cos24 + Ffemury=0
220.92-219.25 + Ffemury=0
Ffemury=-1.67N
 
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  • #2
I see only very small picture. Can not you show a bigger one? ehild
 
  • #3

FAQ: Finding the force of the femur on the knee cap.

1. What is the force of the femur on the knee cap?

The force of the femur on the knee cap is the amount of pressure or load that the femur exerts on the knee cap, specifically at the point where they meet.

2. How is the force of the femur on the knee cap calculated?

The force of the femur on the knee cap can be calculated using the formula F = ma, where F is the force, m is the mass of the femur, and a is the acceleration of the femur on the knee cap.

3. Why is it important to know the force of the femur on the knee cap?

Knowing the force of the femur on the knee cap is important for understanding the biomechanics of the knee joint and the potential impact of activities or injuries on this joint. It can also help in designing treatments or exercises to strengthen the muscles and ligaments surrounding the knee to better support this force and reduce the risk of injury.

4. How does the force of the femur on the knee cap change with different activities?

The force of the femur on the knee cap can vary depending on the activity being performed. For example, activities that involve jumping or running may result in a higher force on the knee cap compared to activities like walking or sitting. Additionally, the force may also change with different body positions or angles of the knee joint.

5. Are there any factors that can affect the force of the femur on the knee cap?

Yes, there are several factors that can affect the force of the femur on the knee cap, including body weight, muscle strength and control, joint alignment, and the presence of any injuries or conditions in the knee or surrounding structures. Additionally, external factors such as footwear, surface type, and type of activity can also impact this force.

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