Is he saying that gravitational force is exactly the same as a force of acceleration?
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No. Nothing immediately to do with force. Also, there is no "force of acceleration". Acceleration is itself NOT a force. Acceleration is the RESULT of the net force.
Consider an object, any object.
It has TWO important properties, solely due to the fact that it is an object.
What are they?
Property 1: it has an intrinsic hindrance to a change in state of motion. We call this its inertial mass. I.e. the m in Newton's second law.
Property 2: it participates in the force of gravity, both as a source and recipient of this force. We call this its gravitational mass...i.e. the m's in Newton's law of gravitation.
Ever since Galileo, it has been a known fact that these two properties of matter are actually the same property of matter. We just call it mass for a shorthand.
Einstein's equivalence principle considers two SITUATIONS whereby which we can MEASURE and OBSERVE the properties of matter we call mass. And claims that no matter what situation you choose, as long as they are equivalent situations...there is NO EXPERIMENT you can do (without looking outside) to discover which situation your immediate environment is undergoing.
The two situations are:
1. your environment is stationary in a background uniform gravitational field.
2. your environment is accelerating through deep space, with an acceleration equal to the g-field in situation 1.
Can you, as an occupant of this environment DO ANY EXPERIMENT to discover which is the case? Remember, you cannot observe anything outside your immediate environment (reference frame). Also, another restriction is that you need to assume the acceleration (hypothetically) never changes no matter what happens.
Einstein's equivalence principle is that you cannot.
Consider an object, any object.
It has TWO important properties, solely due to the fact that it is an object.
What are they?
Property 1: it has an intrinsic hindrance to a change in state of motion. We call this its inertial mass. I.e. the m in Newton's second law.
Property 2: it participates in the force of gravity, both as a source and recipient of this force. We call this its gravitational mass...i.e. the m's in Newton's law of gravitation.
Ever since Galileo, it has been a known fact that these two properties of matter are actually the same property of matter. We just call it mass for a shorthand.
Einstein's equivalence principle considers two SITUATIONS whereby which we can MEASURE and OBSERVE the properties of matter we call mass. And claims that no matter what situation you choose, as long as they are equivalent situations...there is NO EXPERIMENT you can do (without looking outside) to discover which situation your immediate environment is undergoing.
The two situations are:
1. your environment is stationary in a background uniform gravitational field.
2. your environment is accelerating through deep space, with an acceleration equal to the g-field in situation 1.
Can you, as an occupant of this environment DO ANY EXPERIMENT to discover which is the case? Remember, you cannot observe anything outside your immediate environment (reference frame). Also, another restriction is that you need to assume the acceleration (hypothetically) never changes no matter what happens.
Einstein's equivalence principle is that you cannot.