What is the difference between mass and weight? Why do we speak of the astronauts in orbit as weightless?

Question

Another physics paper!!!

Answer 1

Mass is the amount of matter in an object. The more matter has on it, the greater the mass. For example, in an ice cube and a cube of lead, lead exhibits more mass eventhough their volume is the same because it has more compact "matter" (which is the element lead) on it as compared to ice. It is measured in kilograms in MKS system.

Weight is the force exerted by gravity to an object. It differs in different locations in earth (from mountain to lowlands, equator to poles). The moon has 1/6 of the earths gravity, therefore an astronaut has more weigth here in earth. (if he weights 100 pounds, he will weight 20 pounds on moon). It is measured in Newtons.

When a person is in space, he weight zero because there is no Gravity. (gravity is exerted by two matter, maybe the person and a planet, and so on..) He weight zero cause he is at an empty space and has no other object to attract towards him to cause gravity, an therefore no force at all.

Answer 2

Mass is a constant value that measures the amount of matter in an object. Weight is a measure of the force exerted when a mass is accelerated. Weight is usually referred to as the acceleration caused by the earths gravity upon a given object.

Weightless is a bit of a misnomer. Nothing exhibits no weight due to the universal law of gravitation. The universal law of gravitation states that the attraction between two masses is directly proportional to the mass and inversely proportional to the distance. So an astronaut in space exhibiting a relatively small mass at an extended distance from the earth exhibits a low weight caused by gravitational pull of the earth.

Additionally you have a rotational velocity producing a level of centripetal force acting to counteract the gravitational pull of the earth, which is why they orbit the earth rather than crashing into it. When you see video of a space walk the participant looks like they are not moving much because the camera is orbiting the earth at the same rate as the astronaut (relative motion). In actuality they are streaking across the sky at a pretty fantastic rate.

So to summarize nothing ever exhibits no weight. But the sum of the forces can add up to zero. So a space walkers (reduced) weight acting toward the earth is offset by the centripetal force of the obit trying to hurl them into outer space, and they feel weightless. This can actually be quite a confusing sensation and often lead to adverse physical symptoms, since we act under our normal laws of gravity most of our lives.

Answer 3

Gravity is a property of mass. That's basic physics. The amount of mass determines the amount of gravity that a body of mass will pull with. Humans have mass. Humans act as they're own gravitational body. Albeit, very small, that is why astronauts are refered to as having 'micro-gravity'. All bodies in space, (humans, ships, the Sun, the Earth, the Galaxy itself) exert gravitational influences on each other. (The gravitaional pull of the planet Jupiter is exerting a pull against you as I type, even though the Earth's gravitational pull is stronger because your closer to it.) Now, the astronauts are not 'weightless'. To be weightless, there would have to be no mass, and you can't have no mass and still be here. The comparative sizes of a man to the Earth is about equal to the size of a man to an ameoba. Now does a man have just as strong of a relative pull on the ameoba as the Earth does on a man due to the mass of the man? A human body is about 78% water. The Earth's composition is a lot denser than water. So even though the size comparasin's are about equal, the force of gravity is not. Water is a lot less dense than the materials comprised of in the Earth, (the liquid/solid core of iron/nickel, the mantle, rocks, etc.) So the relative pull will be greater for Earth/Man vs. Man/Ameoba. Gravity is really dependant on the amount of mass divided by the amount of area the mass is distributed over. Whatever unit of measure you want to use, as the distance doubles, the force divides by 4. It's called the 'inverse-square' law. The farther two bodies of matter separate, say 1 meter, then when they get to 2meters, the gravitational attraction between the two bodies will be reduced to one-quarter of what it was at 1 meter.
On the inverse, if you decrease the distance by half, the pull of gravity will be increased 4 times. So if you were to decrease the size of the Earth without decreasing it's mass (an important point of note) to say, the size of a beach ball, the gravitational pull of gravity will exceed that of the velocity of light, i.e. become a black hole.

Astronauts are actually in a state of free-fall. EVERTHING around them is going the EXACT same speed. Just like going on an amusement park ride where you rocket straight up, stop and decend back down, when your at the top, just after accelerating to the top, and just before free-fall back down, you would be 'weightless'. Try doing that and take a rubber ball with you, and when you get to the top, release it. It will momentarily hover above your hand like things do for the astronauts in 'weightlessness'. At the altitude they're at, the Earth is still pulling on them, but because of the distance, the gravitational pull of the Earth is however many times less (inverse-square' law) than it would be if they were on it's surface.
I realize this is long, but I hope it answers your question (are you thoroughly confused yet?)

Answer 4

Actually, in orbit around the earth, the acceleration due to gravity is only 3% less than at the ground. Consider that it is gravity that keeps the spaceship in orbit!

The effect of weightlessness in orbit is more like the weightlessness experienced by a body in free-fall off a building or cliff. There is nothing to act against to give the sensation of "weight" (like the firm ground). This is subtle, but correct. Weightlessness in orbit is NOT about far distance from the earth or escaping earth's gravity.

Here is a good description:
http://en.wikipedia.org/wiki/Weightlessness

Answer 5

Mass is an 'intrinsic characteristic' of matter. But what we call 'weight' is the force exerted on mass by a gravitational acceleration. (That's right. Gravity is *not* a force, it is an acceleration ☺)

Astronauts in orbit are *not* outside of the Earths gravity. If they were, the Earths gravity wouldn't be able to hold the Moon in orbit What's really happening in orbit is that the 'centrifugal force' (more properly, centrifugal acceleration) acting on the orbiter is exactly counterbalanced by the acceleration of gravity so that the *total* acceleration acting on the orbiter, astronauts, and anything else 'in orbit' is zero. Since the net acceleration is zero, the net force produced on any mass is zero and they are 'weightless', But they still have mass (and so does everything else ☺)

One of the more dangerous things they have to do is to maneuver relatively large (massive) pieces of equipment. You have to remember that it takes as much force to start something moving as it does to stop it. Several near disasters have occurred because someone forgot that simple truth ☺

Hope that helps.


Doug

Answer 6

mass id measured in grams and kilograms
weight is measured in Newtons and is measured in
kg x gravitational pull.

Since in orbit there is very little gravitational pull compared to on earth, their weight is next to 0, which is termed "weightless". (There is actually a pull, which is why they can orbit around the earth, but the space craft and the astronauts are experiencing the same pull, so relative to the spacecraft, there is no gravitational pull.)

When they would be out of our solar system would they truly be weightless. Even the planetoids Pluto feels a gravitational pull towards our sun.

OR

If the astronauts find that "sweet spot" where the gravitational pull of the earth is equal to the gravitational pull of the moon, it would be more accurate that they are weightless.

Answer 7

Mass is like, our substance, and weight is a very specific force that relates to gravity. The two should not be confused, because on the moon an object would be a different weight but would still have the same mass. Have fun with the paper, I'm studying this in physics too now :)

Answer 8

Mass of any object is same,but the weight of the same object will be different on earth, moon or any other planet. This is because the gravitational force acting on the object is different on different planets. So mass will be the same but weight is w= f = m x g where is the weight equivalent to f which is gravitational force, m is the mass and g is the gravitational acceleration

Answer 9

mass is actually the amount of matter in a substance whereas weight is actually = mg (mass multiplied by g or gravitational force)
the value of mass remains the same whether in equator or the poles but weight of an object varies as value of g is different in diff places . In space value of g =0 hence weight =0 .so astronauts r weightless in space

Answer 10

Mass is the amount of matter in a body. While weight is the gravitational pull of Earth on that body. Thats why astronauts on the moon 'jump' when they walk on the lunar surface. Lunar gravity is only 1/6th of Earth's. So when you have a mass of 50 kg on Earth, your weight on Earth will be 50kg but on moon will be 8 kg.

Astronauts in orbit dont have gravitational forces acting on them, hence they feel 'weightlessness'


The following is a list of the weights of a mass on some of the bodies in the solar system, relative to its weight on Earth:

Mercury 0.378
Venus 0.907
Earth 1
Moon 0.165
Mars 0.377
Jupiter 2.364
Saturn 1.064
Uranus 0.889
Neptune 1.125

Hope this helps