1. Stand with your back and feet against a wall. Have someone place something on the floor at your feet. Try to pick it up.
Why? When leaning over to pick up object we use our keep our centre of gravity between our feet by moving our buttocks back as we lean over. When you are standing against a wall you can't make these adjustments.
2. Stand against a wall sideways with your arm and leg touching the wall, with nothing to hold onto. Lift your other leg straight out away from the wall.
Why? You are using the outside leg to balance. Lifting it would cause the centre of gravity to be outside your feet.
3. The “girls always win” chair lifting challenge. Place dining chair against a wall. Bend over the chair so that your head touches the wall and your upper body is parallel to the floor. Lift the chair to your chest and then stand up.
How does it work? Men and women have their centre of mass in different places. Men tend to have broad shoulders and narrow waists, giving them a higher centre of mass. Adding the weight of the chair causes the centre of mass to be over the chair. To stay balanced men have to use the wall. When he tries to stand, he falls.
Girls and women have their centre of mass closer to their hips. Even with the added weight of the chair, the overall centre of mass is over the feet that the body is able to right itself.