- #1

- 104

- 0

direction, it weighs 10kg. Suppose I'm moving upwards in

a uniform velocity 5m/s , how much would object weigh

now ??

- Thread starter Trojan666ru
- Start date

- #1

- 104

- 0

direction, it weighs 10kg. Suppose I'm moving upwards in

a uniform velocity 5m/s , how much would object weigh

now ??

- #2

arildno

Science Advisor

Homework Helper

Gold Member

Dearly Missed

- 9,970

- 132

If we call r the initial distance from the center of the Earth, r+vt (where v is the velocity you move away with), you should be able to calculate for yourself that ratio of weights, as a function of time.

- #3

- 104

- 0

- #4

arildno

Science Advisor

Homework Helper

Gold Member

Dearly Missed

- 9,970

- 132

Do you think it would increase or decrease when you move away from the Earth?

- #5

- 104

- 0

- #6

- 15,393

- 685

Since you used the colloquial definition of weight, a synonym for mass, the answer is simple: It "weighs" 10 kg, anywhere and everywhere.

That colloquial meaning is not what physicists and engineers mean they talk about "weight". Physicists use the word "mass" to denote mass. Why use the word "weight" when there is already a perfectly good word for mass? Weight in physics has units of force in physics. There are two widely used definitions: The force due to gravitation on the object (mass times gravitational acceleration), and the total of all forces acting on the object except for gravitation.

What arildno is hinting at is mass times acceleration, or Newton's universal law of gravitation. What does that have to say about the force due to gravitation as altitude increases?

- #7

Nugatory

Mentor

- 13,118

- 5,896

Using "weight" in the precise sense of being what a spring scale underfoot would read....

Aside from a tiny effect from inverse square law as you may move away from the center of the earth, the weight will not change if you're climbing at a constant velocity. It will change if you're accelerating or decelerating, so not climbing at a constant velocity.

Have you ever taken a fast elevator in a tall building? As the elevator first starts moving upwards you feel a slight increase in weight; you're accelerating upwards. As the elevator settles down to a steady upwards climb your weight returns to normal (no acceleration) and then as it slows to a stop at the top of the climb you feel momentarily lighter.

Of course the force of gravity on your body is the same throughout, as is your mass; what's changing is the force between you and the floor of the elevator, what we strictly mean by "weight".

- #8

- 104

- 0

- #9

Nugatory

Mentor

- 13,118

- 5,896

If you are moving at a

- #10

- 104

- 0

- #11

- 15,393

- 685

Then why did you persist in saying the weight is 10 kg? Kilograms are a unit of mass, not force.here I'm strictly talking about weight, not mass, consider the mass does not vary because I'm moving with the mass.

That is not the definition of weight used in general relativity (your next post, below). In general relativity, "weight" is what an ideal (spring) scale measures. That's all real forces except gravitation (Newtonian interpretation), or all real forces, period (general relativistic interpretation). Gravitation is not a real force in general relativity.Weight is the product of mass and g.

Where did you get this idea?

- #12

Nugatory

Mentor

- 13,118

- 5,896

That's not what GR says gravity is, but this doesn't matter because GR itself is basically irrelevant in a situation in which the effects of the Newtonian inverse-square law are small enough to ignore.

This is really just an ##F=ma## problem. We're climbing at a constant velocity, so ##a=0##. Therefore ##F## is zero, which can only happen if the downwards force of gravity on our body is exactly balanced by the upwards force on our feet from the scale we're standing on.

- #13

- 887

- 98

10kg. You must accelerate or de-accelerate for the scale reading to change. You can test this in an elevator. Scale reading will change at the beginning and end of the ride.

direction, it weighs 10kg. Suppose I'm moving upwards in

a uniform velocity 5m/s , how much would object weigh

now ??

- Replies
- 1

- Views
- 2K

- Last Post

- Replies
- 6

- Views
- 3K

- Replies
- 6

- Views
- 818

- Last Post

- Replies
- 3

- Views
- 3K

- Replies
- 8

- Views
- 29K

- Replies
- 0

- Views
- 2K

- Replies
- 4

- Views
- 943

- Replies
- 54

- Views
- 4K

- Replies
- 22

- Views
- 1K

- Last Post

- Replies
- 2

- Views
- 1K