A common creationist objection to the theory of evolution is the orbital recession of the Moon. It is well known that the distance between the Earth and Moon is gradually getting larger. Every year, the Moon is roughly 3.8 cm farther away than it was the year before. What creationists claim is that if you run the clock backwards, and let the Moon approach the Earth at that rate, it ends up colliding with the Earth long before the supposed age of the Earth-Moon system, thus showing that the world couldn’t be that old.
The usual objection is over the past 4.6 billion years (the age of the Moon), the rate that it’s been moving away at hasn’t been constant. The mechanics of lunar recession is complicated, having to do with the distribution of oceans and landmasses on the Earth (different distributions produce different gravitational “tugs” on the Moon as it orbits). Today’s rate is actually quite a bit higher than it has been in the past. So directly extrapolating today’s rate into the past won’t actually give you the correct answer.
And then…there’s this:
The Moon is currently 385,000 km away (on average. The Moon’s orbit is actually somewhat eccentric).
385,000 km / 3.8 cm per year = 10.1 billion years. Far older than the accepted age of the Earth.
So even if you do blindly extrapolate backwards, the Moon doesn’t actually end up colliding with the Earth. So not only do creationists not do their research, they also suck at math!