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modulus
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I might sound like an idiot asking this question, but, how does a body have zero weight in free fall??
It doesn't. The true weight--the gravitational force that the Earth exerts on the object--remains. What is zero is the apparent weight, which is the magnitude of the contact force supporting an object. That's what is meant by the term "weightless"--the apparent weight is zero, not the "true" weight.modulus said:I might sound like an idiot asking this question, but, how does a body have zero weight in free fall??
When a body sets in motion inside a fluid(like atmosphere, water) the viscous force of the fluid which retards its own motion starts retarding the motion of the body until all the force the body exerts on the fluid(like gravitational force) becomes zero so the body moves with a constant velocity called terminal velocity.It is commonly applied to falling under gravity but then it is not called"free fall under gravity" because the body does not accelerate under gravity.modulus said:I might sound like an idiot asking this question, but, how does a body have zero weight in free fall??
The apparent weight becomes equal to contact force by Newton's third law, and I had a great discussion on it yesterday.modulus said:I kind of get it... kind of...
I understand that the apparent weight becomes zero, but where is the contact force? And how does the apparent weight (which is a downward force) become equal to the contact force (which is acting in the upward direction)?
If the body is moving under free fall, we neglect air friction, right? So how will it ever reach a terminal velocity, when there is no force of friction to deccelerate the body?
Also, what do you mean by 'no strain in the body'? What relation does it have with the weight of the body. Does having 'no strain on your body' mean that the net of all the forces acting on you are equal to zero?
What we call "apparent weight" is just a measure of the support force. There's no separate downward force on the body, other than its true weight. The contact force is produced by whatever is supporting the body. It's this contact force which creates the stresses in your body that gives you the feeling of having weight--when you remove that support, and thus the stresses, you feel "weightless".modulus said:I kind of get it... kind of...
I understand that the apparent weight becomes zero, but where is the contact force? And how does the apparent weight (which is a downward force) become equal to the contact force (which is acting in the upward direction)?
We often ignore air resistance when talking about free fall, but obviously you cannot ignore it if you want to talk about terminal velocity.If the body is moving under free fall, we neglect air friction, right? So how will it ever reach a terminal velocity, when there is no force of friction to deccelerate the body?
As I said above (and others have explained) it is the contact force that produces the strain in the body (gravity alone acts uniformly and thus produces no stresses). You feel such stresses, for example, when you are sitting in your chair--but the net force on you is zero. When you are in free fall (the only force acting on you being gravity) you experience no stresses and the net force on you is your weight.Also, what do you mean by 'no strain in the body'? What relation does it have with the weight of the body. Does having 'no strain on your body' mean that the net of all the forces acting on you are equal to zero?
Doc Al said:We often ignore air resistance when talking about free fall, but obviously you cannot ignore it if you want to talk about terminal velocity.
Free-fall is defined as motion without any external force except weight. Therefore, free-fall on Earth is not technically possible.vin300 said:Yes, we ignore air resistance when talking about free fall because it does not make a difference, right?
Imagine you are standing on a bathroom scale whilst in free-fall. Both you are the scales are accelerating at the same rate, what would the reading be on the scales?modulus said:But, during free fall you say that the only force acting on the body is its weight, yet, its apparent weight is zero... how is that so?- there is no opposite force acting on it, because it feels no stresses...?
So it does make a difference and is ignored because it would not be the typical free fall. Then I must say skydiving is misinterpreted as free fall and statements like "free-fallers reach their terminal velocity when.." are wrong.Hootenanny said:Free-fall is defined as motion without any external force except weight. Therefore, free-fall on Earth is not technically possible.
I am unsure of what you mean by "does not make a difference".
That's all right.For relatively small objects undergoing low and slow falls, drag will not have a significant impact. However, if one say jumps out of an aeroplane, then drag certainly plays an important role.
The apparent weight is zero because there is no supporting force. As Hootenanny points out, your apparent weight is what a bathroom scale would read.modulus said:But, during free fall you say that the only force acting on the body is its weight, yet, its apparent weight is zero... how is that so?- there is no opposite force acting on it, because it feels no stresses...?
Yes, in physics the term "free fall" means (by definition, as Hoot says) that the only force acting is gravity. In everyday usage, "free fall" has a less strict meaning. If you wish to consider the effect of air resistance, then it's no longer "free fall".vin300 said:So it does make a difference and is ignored because it would not be the typical free fall. Then I must say skydiving is misinterpreted as free fall and statements like "free-fallers reach their terminal velocity when.." are wrong.
Doc Al said:Yes, in physics the term "free fall" means (by definition, as Hoot says) that the only force acting is gravity. In everyday usage, "free fall" has a less strict meaning. If you wish to consider the effect of air resistance, then it's no longer "free fall".
In free fall, the only force acting on a body is gravity. When a body is falling, it is in a state of weightlessness because the gravitational force is canceled out by the force of acceleration. This results in a net force of zero, and therefore the body experiences zero weight.
2.Weight and mass are often used interchangeably, but they have different meanings in physics. Mass is a measure of the amount of matter in an object, while weight is the force of gravity acting on that object. In free fall, the weight of an object is zero, but its mass remains the same.
3.In order for a body to have zero weight, it must be in a state of free fall where the only force acting on it is gravity. This can also occur in orbit, where the body is constantly falling towards the Earth but its horizontal velocity keeps it in a circular path.
4.Astronauts experience weightlessness in space because they are in a state of free fall. In orbit, the spacecraft and everything inside it are falling towards the Earth at the same rate, resulting in a net force of zero on the objects inside. This creates the sensation of weightlessness.
5.No, a body does not have zero weight at the bottom of a deep pool. In this situation, the body is still experiencing the force of gravity from the Earth and the force of buoyancy from the water. These forces are not equal, so the body will have a weight that is not zero.