You must be thinking, "physics posts, biology post, now tips to lose weight? Wonderful!!" Well, no tips to lose weight in this post, ( sorry for that, maybe later ) but I'm going to help you understand a new concept called weightlessness. That is, how to feel 'like' you've lost all your weight, when you very much haven't. And where could we see examples of this concept?
To start with the basics, what is weight? Colloquially we use the terms 'mass' and 'weight' interchangeably. The amount of matter in an object. But, actually mass is the amount of matter in an object and weight is the amount of force with which an object is attracted towards the centre of the Earth ( could be any planet/moon, Earth in our discussion) , and is measured using a spring balance. That said, when we walk, or run or jog for that matter, do you feel any force pulling you down? No. Gravity force cannot be felt. Isn't it? If that's the case, why do you experience soreness when you sit for a long time? What is that pressure that is felt?
The force that acts in the upward direction when you sit is the contact force offered by the chair. Contact force is the force that occurs when two objects are in contact. Gravity on the other hand is not a contact force. Two objects needn't be in contact for Gravity to act. When we sit in our chair, the net force acting on us is zero, so the gravity force must equal the upward contact force. Gravity is not felt, so the force we feel is the contact force equal to our weight. Similar is the case when we stand on the weighing machine. The weighing machine measures the contact force, which is equal to our weight.
Think about this, what if the contact force turns out to be zero. The weighing machine would actually read zero!!?! And we might not feel our weight. Right? Maybe we get the floating-in-the-air feeling? That's good. Now how to make the contact force read zero? Maybe if the chair was falling? Free falling? Then it won't be stable enough to give the contact force. Contact force zero. The person sitting on it will feel weightless!! Ooh la la.
To understand this further, take a paper cup. Punch two holes towards the bottom. One on either side. Fill it with water. Notice water leaking out from either sides. Now drop the glass. How does the water behave? Watch the video from here to learn. Water was momentarily weightless.
Same is the case with a free falling elevator. Elevator whose cable has just snapped and while it's free falling, the unfortunate person or object inside would experience floating and weightlessness.
One another instance is skydiving. When the skydiver jumps from the plane, nothing to give him his contact force. Hence, he feels like he/she is floating. The familiar stomach in your mouth feeling. After a while, the drag force keeps increasing and the skydiver reaches the terminal velocity. In which case, the net force on him being zero, he feels his weight. Just like he were lying down on his bed or sitting in his chair. Then the parachute, sudden increase in drag force, the skydiver feels heavy, momentarily. Finally he reaches a lower terminal velocity and glides down safe.
Have you seen astronauts floating in their spaceship? In movies? That's because of weightlessness video. Explains it wonderfully too. Not because there is no gravity there. There definitely is some amount of gravity there, coz if not for gravity, the spaceship wouldn't orbit the Earth, but fly off into space.( the same as why moon orbits the Earth ) The astronauts feel weightless inside the ship because the ship is falling towards the earth due to gravity and so are the astronauts inside. No contact force. See this
Been to a roller coaster ride? The butterflies in your stomach feeling, which occurs when you've just begun a big descent is also the same weightlessness concept. When the roller coaster takes the descent with you, if fails to offer you your contact force, and you feel like you are lifting off from your seat.
Wonderful! To add on to your excitement, imagine getting into a lift with a weighing machine. And as the lift goes up and down, see if the weighing machine shows you different weights !! Sounds impossible isn't it. Just try it! The weighing machine will actually show weights corresponding to you feeling light or heavy when the lift moves down or up.
Wow! we've learnt a lot of things today. A new force called contact force. The concept of weightlessness. Why we feel light on a roller coaster just at the start of a big drop. Why astronauts float in space, and that it's not because there is no gravity there. And we know how a skydiver feels when he jumps off a plane. Have I inspired you to become a skydiver today? Have I inspired you to become an astronaut today? Do you feel like taking the lift till the highest floor of a tall building just to correlate your experience with what we just learnt? Too much to ask for!! I agree. Have I inspired you to ask thought provoking questions about the simple things that we see in our everyday life? Did you say 'yes'? I say 'mission accomplished'. I can see myself next to Tom Cruise, with a gun in my hand, wearing all black and mission impossible music in the background! Oh gosh, that is mission impossible isn't it! And this is mission accomplished. I think I went too far!! (Sheepish grin) Never mind. Forget that! But remember the lift, the roller coaster, the astronauts and the skydiver and more importantly, the zero reading on the weighing scale!
To start with the basics, what is weight? Colloquially we use the terms 'mass' and 'weight' interchangeably. The amount of matter in an object. But, actually mass is the amount of matter in an object and weight is the amount of force with which an object is attracted towards the centre of the Earth ( could be any planet/moon, Earth in our discussion) , and is measured using a spring balance. That said, when we walk, or run or jog for that matter, do you feel any force pulling you down? No. Gravity force cannot be felt. Isn't it? If that's the case, why do you experience soreness when you sit for a long time? What is that pressure that is felt?The force that acts in the upward direction when you sit is the contact force offered by the chair. Contact force is the force that occurs when two objects are in contact. Gravity on the other hand is not a contact force. Two objects needn't be in contact for Gravity to act. When we sit in our chair, the net force acting on us is zero, so the gravity force must equal the upward contact force. Gravity is not felt, so the force we feel is the contact force equal to our weight. Similar is the case when we stand on the weighing machine. The weighing machine measures the contact force, which is equal to our weight.
Think about this, what if the contact force turns out to be zero. The weighing machine would actually read zero!!?! And we might not feel our weight. Right? Maybe we get the floating-in-the-air feeling? That's good. Now how to make the contact force read zero? Maybe if the chair was falling? Free falling? Then it won't be stable enough to give the contact force. Contact force zero. The person sitting on it will feel weightless!! Ooh la la.
Same is the case with a free falling elevator. Elevator whose cable has just snapped and while it's free falling, the unfortunate person or object inside would experience floating and weightlessness.
One another instance is skydiving. When the skydiver jumps from the plane, nothing to give him his contact force. Hence, he feels like he/she is floating. The familiar stomach in your mouth feeling. After a while, the drag force keeps increasing and the skydiver reaches the terminal velocity. In which case, the net force on him being zero, he feels his weight. Just like he were lying down on his bed or sitting in his chair. Then the parachute, sudden increase in drag force, the skydiver feels heavy, momentarily. Finally he reaches a lower terminal velocity and glides down safe.
Have you seen astronauts floating in their spaceship? In movies? That's because of weightlessness video. Explains it wonderfully too. Not because there is no gravity there. There definitely is some amount of gravity there, coz if not for gravity, the spaceship wouldn't orbit the Earth, but fly off into space.( the same as why moon orbits the Earth ) The astronauts feel weightless inside the ship because the ship is falling towards the earth due to gravity and so are the astronauts inside. No contact force. See this
Been to a roller coaster ride? The butterflies in your stomach feeling, which occurs when you've just begun a big descent is also the same weightlessness concept. When the roller coaster takes the descent with you, if fails to offer you your contact force, and you feel like you are lifting off from your seat.
Wonderful! To add on to your excitement, imagine getting into a lift with a weighing machine. And as the lift goes up and down, see if the weighing machine shows you different weights !! Sounds impossible isn't it. Just try it! The weighing machine will actually show weights corresponding to you feeling light or heavy when the lift moves down or up.
Wow! we've learnt a lot of things today. A new force called contact force. The concept of weightlessness. Why we feel light on a roller coaster just at the start of a big drop. Why astronauts float in space, and that it's not because there is no gravity there. And we know how a skydiver feels when he jumps off a plane. Have I inspired you to become a skydiver today? Have I inspired you to become an astronaut today? Do you feel like taking the lift till the highest floor of a tall building just to correlate your experience with what we just learnt? Too much to ask for!! I agree. Have I inspired you to ask thought provoking questions about the simple things that we see in our everyday life? Did you say 'yes'? I say 'mission accomplished'. I can see myself next to Tom Cruise, with a gun in my hand, wearing all black and mission impossible music in the background! Oh gosh, that is mission impossible isn't it! And this is mission accomplished. I think I went too far!! (Sheepish grin) Never mind. Forget that! But remember the lift, the roller coaster, the astronauts and the skydiver and more importantly, the zero reading on the weighing scale!
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