# Centre of Mass Wall Tricks

## Learning Objectives

Students will investigate the importance of centre of mass with respect to balance.

## Associated Curriculum Topic

Form and Function

## Materials

• a wall
• a few brave students!

## Introduction/Motivation

The centre of mass is a very important aspect to balancing on your own two feet. When your centre of mass is no longer directly above your support (your feet), you are more likely to fall over. This activity will demonstrate the importance of centre of mass to the students while they try to stand on their tippy toes with their nose to a wall or lift one foot while leaning up again a wall.
Your centre of mass is approximately located around your naval (belly button). When you are standing flat-footed on the floor, your centre of mass is directly above your feet, in the middle. In order to stand on your tiptoes and be stable, you need to get that centre of mass directly above your toes, which means that you need to tip forward slightly. If you have your toes and nose against a wall, however, it is impossible for you to lean forward without going through the wall. As a result, your centre of mass remains exactly where it would be if you were flat footed on the ground which means you can’t go up onto your tippy toes.

The same principles apply when you’re standing perpendicular to the wall, so that your ankle, hip and shoulder are all touching the wall. If you try to lift your left foot, you need to lean slightly to the right in order to shift your centre of mass to be above the support point. If your right side is firmly against the wall, you will not be able to shift your centre of mass and therefore can not stand on your right foot.

## Procedure

As a class together, get everyone to stand on their tiptoes for 5 seconds. Then get everyone to stand on their left leg for 5 seconds. This part is easy! Now ask for volunteers for a more difficult task …

### Nose to wall:

• Each student can try this activity as long as they have a spot along a flat wall.
• Place your toes and nose against the wall.
• Try to raise yourself up onto your tippy toes – it is impossible!

### Hip, ankle, and shoulder to wall:

• Each student can try this activity as long as they have a spot along a flat wall.
• Stand along the wall so that one side of your body is touching the wall. Ensure that you have your ankle, hip and shoulder all touching the wall at the same time.
• Try to lift the foot that is on the opposite side to the wall – it is also impossible!

## Investigating Questions

• What is centre of mass?
• Where is your centre of mass?
• Why can’t you go up onto your tippy toes when standing with your nose to the wall?
• Why can’t you raise your opposite foot when you are leaned up against the wall?