How do you deal with the density of gold in TV shows and movies?
It felt like it went on for a couple of weeks. I kept getting the same promoted tweet on twitter (I can’t even find it now). It was an ad for the show Money Heist on Netflix.
I really don’t know much about the show, but the ad shows some people scuba diving inside of a flooded vault and picking up some gold bars. Like this.
It shouldn’t be a surprise, but they didn’t use real gold here. Oh, it looks like it’s really underwater — but there’s no way you could hold up gold like that. Even underwater, that gold would be legitimately heavy. The reason: gold is super dense. Like really, really dense.
What the heck is density? It’s a property of a substance (not an object). It is the ratio of the object’s mass divided by its volume (mass per unit volume). Some people use the symbol d for density, but in physics we usually use the Greek letter ρ (rho).
Gold has a density of 19.32 grams/centimeter³ (g/cm³) or 1.932 x 10⁴ kg/m³. Just compare this to some other substances:
- Water = 1 g/cm³.
- Aluminum = 2.7 g/cm³.
- Copper = 8.96 g/cm³.
- Cork = 0.2 g/cm³.
- Lead = 11.35 g/cm³.
But what does this feel like? How about an example. Suppose you grab a penny (one before 1984 that’s mostly copper). This has a mass of 2.5 grams — go ahead an actually pick it up so you know what 2.5 g feels like. Now, if you had a coin the exact same size but made of gold it would have a mass of 5.39 grams. It would be like holding two pennies in the space of one. If you had a gold penny, you could easily feel it (plus — it would be gold and that’s kind of awesome).
OK, but what if you have the object underwater? What would it feel like then? Let’s say you are underwater and holding a block in your hand. There will be three forces acting on that block (assuming that it sinks and doesn’t float).
- The downward pulling gravitational force due to the interaction with the Earth (m*g where g = 9.8 N/kg).