Normally I try to provide some activities which are fairly easy to do. Not this week. This week, we have a couple of balance activities which are impossible to do.
Warning: Take care - you will overbalance when trying these activities.
You will need
A wall
A chair. Try to use one that's the right size for your height.
What to do
Activity 1: lifting a chair
Place the chair facing the wall, so that when you sit in the chair you can just reach the wall.
Stand with your back to the wall, facing the chair.
Stand against the wall so your knees are straight and your feet and backside are up against the wall.
Keeping your knees straight and your feet and backside against the wall, try to lean forward and pick up the chair.
Activity 2: lifting your foot
Stand with the wall to your right.
Move up against the wall, so your right foot is against the wall and your right cheek is against the wall. (You may need to turn your upper body so your right arm is behind you)
Slowly, try to lift your left foot.
What's happening?
Every object has a point called the centre of mass, which is sometimes called the centre of balance or centre of gravity. An object's centre of mass is the point it would balance on. Gravity pulls down on an object as though all of that object's mass were concentrated at one spot: The centre of mass. Your centre of mass is somewhere near your belly-button, although the exact point changes depending on what position you are in.
If your centre of mass is above one of your feet, or above a point somewhere between your feet, then you can balance easily. If your centre of mass moves so it isn't supported, gravity will pull down on your centre of mass and you will start to topple over.
Normally, to pick up the chair you would move some of your weight backwards, behind your feet, to balance the extra weight of the chair in front. This would let you keep the combined centre of mass of you and the chair above your feet. With the wall behind you, you can't move any of your mass behind your feet, so when you lean forward and grab the chair, the combined centre of mass of you and the chair goes beyond the tips of your toes. If you could have lifted the chair off the ground, you would have instantly started to fall forwards until the chair hit the ground again.
Similarly, when we balance on one leg, we normally put some of our weight on either side of the foot, so the mass on one side balances the mass on the other side. This places your centre of mass above your foot. When you were leaning against the wall, you couldn't move your centre of mass above your right foot, because the wall was in the way. If you had lifted your left foot, your centre of mass would be unsupported and you would start to fall to the left. When you try to lift your foot slowly, you can feel your cheek coming away from the wall, so you stop.
Place the chair so you can sit in it and touch the wall.
With your feet and backside against the wall, try to bend forward and lift the chair.
Lean against the wall, with your right foot and cheek touching the wall. You may need to twist your arm behind you.
