- #1

parshyaa

- 307

- 19

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter parshyaa
- Start date

- #1

parshyaa

- 307

- 19

- #2

A.T.

Science Advisor

- 11,657

- 2,951

Per definition.so tell me how real forces are frame independent?

- #3

parshyaa

- 307

- 19

Ok I agree, but can you give me a reason or explanation which made scientist or anyone to frame it as a definition. how can you say that this definition is correct.Per definition.

- #4

A.T.

Science Advisor

- 11,657

- 2,951

Definitions are neither correct nor false.how can you say that this definition is correct.

- #5

- 13,291

- 5,698

This can be proved from the Newton second law

$$F=m\frac{d^2x}{dt^2}.$$

The transformation from one inertial frame to another is given by the Galilean transformation

$$x'=x+vt ,$$

where ##v## is a constant velocity of the frame relative to the other frame. Since this transformation is linear in ##t##, we have

$$\frac{d^2x'}{dt^2}=\frac{d^2x}{dt^2} .$$

Therefore, ##d^2x/dt^2## is frame independent. Assuming that mass ##m## is also frame independent, from the Newton second law above it follows that the force ##F## is frame independent. Q.E.D.

- #6

A.T.

Science Advisor

- 11,657

- 2,951

so tell me how real forces are frame independent?

Real forces are frame independent even across non-inertial frames, so I assumed this is what the OP asks about. As for the main question, Newtons 3rd Law holds only in inertial frames.The transformation from one inertial frame to another

- #7

parshyaa

- 307

- 19

Yes you are right that Newtons third law is frame dependent, because fictitious force can't be felt, its a imaginary force, then how it can have a reaction pair , thanks.Real forces are frame independent even across non-inertial frames, so I assumed this is what the OP asks about. As for the main question, Newtons 3rd Law holds only in inertial frames.

- #8

parshyaa

- 307

- 19

Yoo right , we can also prove it without using galilean transformation,let S and S' be inertial frame of reference, let 'P' be a particle in S', therefore aPS' = aPS - aS'S, since S' is moving uniform to S , aS'S = 0 , therefore aPS' = aPS , as accelaration of particle is same in both frames and mass is same(here) , force will also be same.This can be proved from the Newton second law

$$F=m\frac{d^2x}{dt^2}.$$

The transformation from one inertial frame to another is given by the Galilean transformation

$$x'=x+vt ,$$

where ##v## is a constant velocity of the frame relative to the other frame. Since this transformation is linear in ##t##, we have

$$\frac{d^2x'}{dt^2}=\frac{d^2x}{dt^2} .$$

Therefore, ##d^2x/dt^2## is frame independent. Assuming that mass ##m## is also frame independent, from the Newton second law above it follows that the force ##F## is frame independent. Q.E.D.

- #9

David Lewis

- 842

- 251

For the same reason time moves from past to future....my question was only why gravitational force is attractive?

- #10

jbriggs444

Science Advisor

Homework Helper

- 11,573

- 6,221

Before asking how a fictitious force can have third-law partner, you must ask whether it has a third-law partner.Yes you are right that Newtons third law is frame dependent, because fictitious force can't be felt, its a imaginary force, then how it can have a reaction pair , thanks.

Since it does not have a third law partner, the first question does not arise.

Share:

- Last Post

- Replies
- 28

- Views
- 2K

- Replies
- 127

- Views
- 4K

- Replies
- 6

- Views
- 948

- Replies
- 21

- Views
- 1K

- Last Post

- Replies
- 14

- Views
- 6K

- Last Post

- Replies
- 17

- Views
- 829

- Last Post

- Replies
- 8

- Views
- 1K

- Last Post

- Replies
- 4

- Views
- 904

- Replies
- 16

- Views
- 657

- Replies
- 2

- Views
- 402