Not racing cars! It’s racing Jars!!

  1. Two cylinder shaped jars with lids
  2. Water
  3. Two planks of wood which will make the ramp (You can also use plastic instead of wood)
  4. Some phone books or encyclopedias or something that can be used to prop one end of the ramp up.

  1. At first, fill up one jar with water.
  2. Now screw the lids of both jars as tightly as possible.
  3. Make two ramps with stacks of books and the plank of wood.
  4. Hold both of the jars at the top of two different ramps at the same time.
  5. Now release the jars.
  6. Record which jar reaches the bottom of the ramp first.

  1. At first you will see that the jar full of water rolls faster.
  2. As the race continues you will see that the water jar is slowing down and the other jar wins the race.
Before the start of the race most people would assume that the jar filled with water should win because of its weight. Even when the two jars first start rolling, the water jar rolls faster than the jar with nothing inside. However, the jar filled with water rolls faster not because it’s heavier but because it has evenly distributed weight. The empty jar is actually not empty but it is full of air. So the air filled jar is heaviest at its edges and therefore has a non-uniform weight distribution. It’s harder to accelerate the empty jar than the full jar at first.

As the race continues, the jar filled with water slows down. This happens because it’s heavier than the empty or air filled jar. Because it is heavier, the water filed jar experiences more friction between the jar and the ramp than the empty or air filled jar. This friction hinders an objects speed. The heavier the object is the more friction it will experience and the slower it will get.

So the empty or air filled jar is less hindered and the water filled jar is more hindered by friction. So as the race continues, the water filled jar will get slower and slower at every passing moment but the empty or air filled jar will get less slower. So eventually the water filled jar gets slower than the empty or air filed jar. Thus the empty jar wins the race!


When two adjacent objects or surfaces move or try to move in contact with each other, an opposition is created against their moving velocity. This opposition can be called friction. The force which is created by this opposing force is called friction force.

  1. Try reducing the friction between the jars and the ramp by using a more slippery material or maybe using lubricant on the ramp like oil will do the trick.
  2. Raise the ramp to see the effects.
  3. Lower the ramp to see the effects.


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