The goal of “gotchas” is to help you avoid common errors. (Not that your teacher’s tests would ever try to make you commit any of these errors!)

Confusing weight and mass. You do not weigh 70 kilograms, or 80, or 60. However, those values could very well be your mass, which is an unchanging value that reflects your resistance to a change in motion.

Converting units with factors incorrectly oriented. There could probably be an essay written on this topic. Make sure the units cancel! is probably the best advice we can give. For example, if you are converting meters per second to miles per hour, begin by multiplying by a conversion fraction of 3600 seconds over one hour. This will cause the seconds to cancel and hours to be in the right place. (If this is not clear, write it down and strike out units. If it is still unclear, do some practice problems.) In any physics calculation, checking that the units on each side are consistent is a good technique.

Carelessly adding or subtracting numbers in scientific notation that have different exponents. The exponents must be the same before you can add or subtract the leading values.