Final answer:
Bending your knees when jumping down from a table to the ground is helpful because it increases the time over which the force acts, reducing the risk of injury and fractures.
Step-by-step explanation:
When jumping down from a table to the ground, it is helpful to bend your knees when you hit the ground because it increases the time over which the force acts. This means that the force on your legs is spread out over a longer period, reducing the impact and decreasing the risk of injury. Rolling on the ground or landing with a parachute also extends the time of impact, further cushioning the shock. When you land stiff-legged, the force on your legs can be immense, potentially causing fractures in your bones.