Conserving momentum is when no momentum is created or destoryed.
The first step is to put on the rubber band on one of the sleds and then weigh the sleds and measure the length of the sleds. The next step is to hook up the vaccum cleaner to the air track and put the 2 photo gates underneath the air track and put the 2 sleds on the air track. The third step is to turn on the vaccum and crash the sleds together. The next step is to measure how fast each sled was going by using the 2 photo gates. The last step is to record the results.