Why we feel weightless in a lift which is going to the lower floor?
Great question. My old apartment building used to have a super fast elevator, so I'd jump when we'd reach the top trying to touch the ceiling.
Before we begin, it's important to distinguish between Acceleration and Velocity. Velocity is your speed in a direction. Acceleration is the rate of change of that speed. So slowing down or speeding up is an acceleration. It's also important to define what we mean when we say "weight." If we say that weight is the attractive force of Earth's gravity on our mass, then our weight isn't going to change, no matter how the elevator is moving.
What you're feeling in an elevator isn't weight, it's the force that the elevator is exerting on your feet. If you're in an elevator car, not moving (let's call this "at rest"), gravity is pulling you down. Your feet are pressing down on the floor, and the floor is pushing back up on your feet. The amount you're pushing down on the floor is ALWAYS equal to the amount that the floor is pushing back up on you. (Newton's Third Law) When the car is at rest, the amount the floor is pushing back up on you just so happens to be the same amount that the Earth is pulling down on you. At this point, we say that the forces on you are "balanced".
However, anytime the elevator is accelerating downward, you will feel less force from the elevator pressing up on your feet. (Basically, when the elevator is going downwards AND increasing it's speed, you can call that downward acceleration. It's the same thing when the elevator is moving upwards and slowing down. In both cases the speed is increasing in the down direction.) Newton's Second Law states that the acceleration of an mass is directly proportional to the force applied to the mass. So since the elevator is accelerating downward, the force that the elevator is applying to your feet decreases. Your weight (force of Earth's gravity pulling on your mass) is still the same, so you have unbalanced forces, and your body starts accelerating downward as well.
The bottom line is that if you add up all of the forces on an object and they all cancel each other out, then there is no acceleration. But if there is an unbalanced force, the object will accelerate, or if there is an acceleration, there must be an unbalanced force. So your weight is always the same, it's just that you feel less force from the elevator floor on your feet when you're accelerating downward.
I hope this helps!
Great question. My old apartment building used to have a super fast elevator, so I'd jump when we'd reach the top trying to touch the ceiling.
Before we begin, it's important to distinguish between Acceleration and Velocity. Velocity is your speed in a direction. Acceleration is the rate of change of that speed. So slowing down or speeding up is an acceleration. It's also important to define what we mean when we say "weight." If we say that weight is the attractive force of Earth's gravity on our mass, then our weight isn't going to change, no matter how the elevator is moving.
What you're feeling in an elevator isn't weight, it's the force that the elevator is exerting on your feet. If you're in an elevator car, not moving (let's call this "at rest"), gravity is pulling you down. Your feet are pressing down on the floor, and the floor is pushing back up on your feet. The amount you're pushing down on the floor is ALWAYS equal to the amount that the floor is pushing back up on you. (Newton's Third Law) When the car is at rest, the amount the floor is pushing back up on you just so happens to be the same amount that the Earth is pulling down on you. At this point, we say that the forces on you are "balanced".
However, anytime the elevator is accelerating downward, you will feel less force from the elevator pressing up on your feet. (Basically, when the elevator is going downwards AND increasing it's speed, you can call that downward acceleration. It's the same thing when the elevator is moving upwards and slowing down. In both cases the speed is increasing in the down direction.) Newton's Second Law states that the acceleration of an mass is directly proportional to the force applied to the mass. So since the elevator is accelerating downward, the force that the elevator is applying to your feet decreases. Your weight (force of Earth's gravity pulling on your mass) is still the same, so you have unbalanced forces, and your body starts accelerating downward as well.
The bottom line is that if you add up all of the forces on an object and they all cancel each other out, then there is no acceleration. But if there is an unbalanced force, the object will accelerate, or if there is an acceleration, there must be an unbalanced force. So your weight is always the same, it's just that you feel less force from the elevator floor on your feet when you're accelerating downward.
I hope this helps!
