Elevators disrupt your sense of gravity in strange ways. You can feel it under your feet as the elevator rises. For a moment, the floor felt stronger than usual. As the elevator slows down, the pressure is relieved and your body becomes temporarily lighter.
When you step on the scale in the rising elevator, the number jumps. The value decreases when you slow down and stop. On the descent, the opposite happens.
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Simply put, an elevator can feel heaviest at two points: when it starts to ascend (accelerating upwards) and when it decelerates at the end of its descent (as it decelerates downwards). But the explanation depends on what “heaviness” actually means and what your body feels.
“The word ‘weight’ in physics has many different meanings,” Miguel Morales, a professor of physics at the University of Washington in Seattle, told Live Science. In physics, weight refers to at least three related concepts, Morales said. It’s the mass (how much matter it’s made of), the force of gravity pulling on the person, or how hard the scale below the person is pushing up.
“If you’re just standing still, they might all be the same thing,” Morales said. “But as soon as the elevator starts accelerating or decelerating, you get three different answers. It’s just physics.”
No matter what the elevator does, your mass never changes. Gravity near the Earth’s surface also remains essentially the same at the bottom and top of a building. What changes is the third definition: how strongly the scales are pushed upwards. This upward pressure is what the scale actually measures.
look at gravity
This distinction reveals something counterintuitive. “Humans can’t feel gravity; they never could,” Jason Burns, a physics professor at the University of Idaho, told Live Science.
Burns pointed to the astronauts aboard the International Space Station. “The actual gravity of Earth in the sky is about the same as it is here,” he said. “But they’re not feeling it.”
It’s not because gravity disappears in orbit. At the station’s altitude (about 250 miles or 400 kilometers above Earth), Earth’s gravity is still about 90% as strong as at the Earth’s surface. The difference is that the astronauts and space station are continuously free-falling towards Earth.
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The station is moving laterally at more than 17,000 miles per hour (27,300 km/h). As it falls, the Earth curves away beneath it. Instead of hitting the ground, it keeps coming off the ground. As a result, constant falls occur around the Earth.
The astronaut and the space station fall together at the same speed, so there is no need for the floor to push the astronaut up. And that upward pressure is what we actually feel as weight (also known as normal force).
On Earth, the ground constantly pushes you up to prevent you from falling. There is no such propulsion in orbit. The astronauts are still under the influence of gravity, but there is nothing to prevent them from falling. Without the floor pushing up, you feel weightless.
Why does it feel heavier or lighter when I ride an elevator?
Elevators temporarily change how hard the floor pushes you back. As the elevator begins to rise, you must also accelerate upwards. “When you start climbing, you feel heavy,” Burns says. “The elevator is pushed back harder than normal to accelerate you upwards.”
In a typical building elevator, the additional acceleration is approximately 1 meter per square meter. This is equivalent to about 1/10 of Earth’s gravity. For someone who normally weighs 150 pounds (68 kilograms), this would temporarily add about 10% to the reading on the scale. The scale may read approximately 165 pounds (75 kg) instead of 150 pounds.
Morales explained the same effect from a scale perspective. “Gravity hasn’t changed at all,” he says. “But now, for you to gain speed, something has to be pushing you up harder than gravity. And your weight on the scale increases.”
Once the elevator reaches a certain speed, it stops accelerating. Even though it is still moving, gravity and upward balance are pushed out again and the scale returns to its normal value.
The opposite happens when the elevator slows down and stops at the top. Even though it is still moving upwards, the elevator has to accelerate downwards slightly to slow down.
Gravity has not changed. But since the elevator is accelerating downward, it doesn’t have to push up on the floor as hard to control its movement. The less upward push (normal force), the lower the scale reading.
“I feel like I’m a little brighter,” Morales said.
The same pattern repeats on the way down. When the elevator accelerates down, the floor pushes up less than usual, making you feel lighter. But when you approach the bottom and slow down to a stop, the acceleration picks up again and you feel heavy again.
This everyday experience turns out to be related to one of the most important ideas in modern physics.
“This is an effect that Einstein first noticed when he was developing his theory of general relativity,” Burns said. This insight, known as the equivalence principle, helped Einstein understand gravity not as a force, but as a result of acceleration and the curvature of space-time itself.
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