The femur is the long bone in your upper leg that connects your hip to your knee. It's the longest, strongest, and heaviest bone in the human body. When you run, jump, or even just stand up, your femur supports your body weight and transfers force between your hip and knee.

The femur is incredibly strong because it needs to be. Scientists have found that a healthy femur can withstand pressure of up to 1,800 pounds before breaking. That's roughly the weight of a small car! This strength comes from the bone's dense, thick structure and its slightly curved shape, which helps distribute weight efficiently.

You can't see your femur because it's buried deep inside your thigh, surrounded by some of the body's largest muscles. The top of the femur has a ball-shaped end that fits into a socket in your hip bone, forming the hip joint. The bottom connects to your knee. When doctors need to examine a broken femur, they use X-rays to see through the muscle and skin.

Paleontologists studying dinosaur fossils often identify species by examining their femurs, since these bones reveal important information about how large an animal was and how it moved.