Would You Weigh Less in a Descending Elevator?

TL;DR

Yes, you would weigh less in a descending elevator because the scale measures the normal force, which decreases as the elevator accelerates downward. Jumping inside the elevator won't stop its fall, and your position relative to the elevator will remain unchanged unless you can jump high enough to reach the ceiling.

Transcript

Transcriber: tom carter Reviewer: Bedirhan Cinar You step into an elevator. It starts going down, fast. What would happen if you jumped right when it started going down? Would the ceiling hit your head? Ouch! Do you stay suspended in the air while the elevator plummets down? Let's examine the elevator problem one step at a time. First, consider a s... Read More

Key Insights

• 🫷 A scale pushes up on us with a force equal to our weight to counteract the force of gravity pulling us down.
• ⚖️ When the elevator accelerates downward, the force pushing up on the scale decreases, causing a smaller reading on the scale.
• ✋ Jumping in the elevator won't alter its movement or stop its fall unless you can reach the ceiling.
• 🧘 The relative position of individuals inside the elevator remains the same as gravity affects both the person and the elevator.

Questions & Answers

Q: Why does the scale push up on us when we stand on it?

The scale pushes up on us to counteract the force of gravity pulling us down. This upward push is called the normal force and is necessary for us to remain stationary on the scale.

Q: Why does the scale read a smaller number when the elevator starts falling?

The scale reads a smaller number because the acceleration of the elevator downward reduces the force pushing up on the scale. The scale's reading is proportional to the force it exerts, which decreases as the elevator accelerates.

Q: Can jumping in the elevator stop its fall?

No, jumping in the elevator won't stop its fall. The relative position of an individual inside the elevator remains the same as gravity acts on both the person and the elevator. Jumping can only change your position relative to the elevator if you can reach the ceiling.

Q: What would happen if the elevator accelerated upward and the cable holding it was cut?

If the elevator accelerated upward and the cable holding it was cut, the elevator would continue to move upward due to its inertia. However, once the upward acceleration stops, gravity would eventually cause the elevator to fall back down.

Summary & Key Takeaways

• When standing on a scale in a stationary elevator, the scale pushes up on you with a force equal to your weight to counteract gravity.

• As the elevator accelerates downward, the force pushing up on the scale decreases, causing the scale to read a smaller number.

• Jumping in the elevator won't stop the fall, and the elevator's movement won't change your relative position inside unless you can jump up to the ceiling.