You will need:
- 3 jars of the same size (1 empty, 1 filled with jam, 1 filled with water)
- Inverted wooden table
- Carpeted area or cushions
Bet your friends to figure out which jar would win.
INSTRUCTIONS
- Set up your ‘race track’. Invert a wooden or plastic table and place it at an angle from the ground so that your jars may roll downwards.
- Make sure to have either a carpet or some cushions at the end of the table so that the jars may not break or crack as they reach the bottom.
- Now, ask your friend to judge which jar wins.
- First place the empty jar and the jar filled with jam at the top of the inverted table and release both jars together so that they may roll to the bottom.
- Next place the empty jar and jar filled with water at the top of the inverted table; release both jars at the same time.
- Lastly, place the jar filled with jam and jar filled with water at the top of the inverted table and release both at the same time.
RESULT
Unlike dropping the jars, where gravity does its work and pulls a heavier object faster towards the ground, when we roll an object, its centre varies based on the distribution of weight. The more the weight is centred in the jar, the smoother it rolls. If the weight is distributed outwards, the rolling object will take a more curved path downwards making it slower. As a result, the jam jar being filled has equal distribution of weight and rolls smoothly. The empty jar, however, has no weight inside and all its weight is made up by the glass of the jar, giving it a curved path as it rolls. Water being a liquid does not rotate with the jar, resulting in all the weight of the jar being focused in the centre and making it roll the fastest.
