How Much Does a Shadow Weigh?

TL;DR

Shadows can't be weighed, but the objects they fall on are affected by light's energy, and the speed of light is slower in materials than in a vacuum.

Transcript

Hey, Vsauce. Michael here. And I'm sure that we all love to have fun with hand shadows, but how much does a shadow weigh? It might sound like a silly question, because it is. I mean, a shadow cannot be put on a scale and weighed. But the material that it falls on top of can be weighed. And we know that light has energy. In fact, when light encounte... Read More

Key Insights

• 🏋️ Shadows themselves cannot be weighed, but the objects on which they fall can be.
• 🙂 Sunlight exerts a force on objects on Earth, causing them to be pushed slightly.
• 🙂 Light travels slower in materials than in a vacuum, and objects can outpace light in a material without breaking the speed of light.
• 🙂 Photonic booms occur when charged particles move faster than light in a material, causing photons to give off radiation.
• 🚄 Astronauts have reported seeing flashes of light, possibly caused by high-speed particles causing photonic booms inside their bodies.
• 🐎 Pushing a rigid object transmits information through compression waves at the speed of sound in the object's material, not the speed of light.
• 🐎 The speed of push is not instant and is slower than the speed of light.

Questions & Answers

Q: Can shadows be weighed?

Shadows themselves cannot be weighed, as they are the absence of light. However, the objects on which shadows fall can be weighed.

Q: How does sunlight affect objects on Earth?

Sunlight exerts a force on objects on Earth, pushing them slightly. Over a larger surface area, such as a city, sunlight can cause a measurable increase in weight.

Q: What is the third astronomical body that can cast shadows on Earth?

The third astronomical body that can cast shadows on Earth is Venus. Venusian shadows have been observed by using a cutout in the shape of Venus and pointing it at the sky.

Q: Can objects move faster than the speed of light in a medium?

No, objects cannot move faster than the speed of light in any medium. The speed of light in a vacuum is the universal speed limit, but objects can outpace light in a material.

Summary & Key Takeaways

• Shadows themselves cannot be weighed, but the objects they fall on can be.

• Sunlight exerts a force on objects on Earth, causing them to be pushed slightly, with larger effects over larger surface areas.

• Light can push objects and travel slower in materials, resulting in phenomena such as photonic booms and Cherenkov radiation.