# How to Use Physics to Tell If That Steph Curry Video Is Real

A few weeks before, sports illustrated tweeted this video from Golden State Warriors point guard Steph Curry it went viral immediately. It shows him shooting at the basket – from the other side of the field. The ball goes in. OK, I can believe that. He is a notoriously great marksman. But then he turns and grabs another ball and shoots again… and does it. And then again. And again. And a fifth time.

So is it real or fake? Let’s use statistics and physics to find out.

Basic Probability

Physicists don’t usually jump straight into the most complicated version of a problem. Instead, they make a rough guess, often referred to as a “back calculation.” So let’s make some approximations about the probability of making five shots in a row across the entire field.

We can start with a simple experiment to try at home – all you need is a coin. Make a prediction: will it end up heads or tails? If you don’t have psychic powers, you have a 50 percent chance of guessing correctly. It’s best to think of this as a fraction of 1, so that would be a probability of success with a value of 0.5.

What if you want to predict the outcome of two coin tosses in a row? In this case you would have a probability of 0.5 for the first flip and another 0.5 for the second. The total probability is the product of these two: 0.5 × 0.5 = 0.25. That’s a one in four chance of getting it right. This makes sense because there are four possible flipping outcomes: HH, HT, TH, TT.

But if you wanted to predict five flips in a row? That would be (0.5)5 = 0.031. You only have a 3 percent chance of correctly predicting all outcomes.

Do you see where this is going? We can apply the same idea to basketball. Assuming Steph Curry’s skills are such that he has a 50/50 chance of making a full shot (which would be amazing). If that were true, his chance of getting five in a row would be 3 in 100. That’s actually not too bad. If you wanted to make a viral video, you could just keep throwing balls until you get five in a row. It may take all day, but it should be possible.

It gets much worse, however, if you assume a shot with lower chances of success. What if you could only hit 1 in 20 of those full court shots? (That would be 0.05.) In this case, the probability of sinking five times in a row would be 0.00003 percent. Good luck with it.

Or how about this? Curry takes five shots. What if he has a 50 percent chance of making it? all five in a row? He would need a hit probability of 0.87 per shot to get (0.87)5 = 0.5. Just compare that to the probability of making a free throw – which is a lot easier because the player is much closer to the basket – somewhere between 0.7 and 0.8.

https://www.wired.com/story/how-to-use-physics-to-tell-if-that-steph-curry-video-is-real/ How to Use Physics to Tell If That Steph Curry Video Is Real

### Zack Zwiezen

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