Gravity's Acceleration and its Effect

In summary: But if someone was inside a small elevator that was travelling upwards at the same rate as the surface of the Earth, they would not feel the upwards normal force, since the force of gravity pulling them down would be cancelling out the upwards force.
  • #1
Greatness
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So, one of Newton's Laws of Motion is -F(sub)1 = F(sub)2.

Gravity is (generally) pulling us down with an acceleration of -9.8 m/s^2 where negative is downwards. Because of the above law, it has been said that this is felt upwards in objects. Why do I only feel gravity downwards?
 
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  • #2
Those forces act on different objects. Gravity pulls you down with some force; you pull the Earth up with the same force.
 
  • #3
It is not felt upwards because of Newton's 3rd Law. When you are standing on level ground, there is a normal force from the ground on you which points upwards and tends to cancel the gravitational force, due to the Earth, pointing downwards from your center of mass. When you are walking on the surface of the earth, the ground pushes up on you and you will of course feel this; the normal force in such a scenario just happens to cancel out the force of gravity pulling you down, allowing you to stay on the level ground. This normal force however is not a reaction force due to the gravitational force exerted by the Earth on you! The reaction force of the Earth's gravity pulling on you is simply your gravitational force pulling back on the Earth.

As stated above, it is true that what you feel is the upwards pointing normal force from the ground on you. In fact, what Einstein said is that if you were completely sealed in a small elevator, you would have no way of telling if you and the elevator were at rest in a downwards pointing uniform gravitational field of magnitude ##g## or you and the elevator were accelerating upwards with magnitude ##g## in free space. This upwards acceleration of magnitude ##g## is what you feel. In the case of a person standing on the surface of the Earth, you feel the upwards normal force, since the ground is pushing up on you.
 

1. What is gravity's acceleration?

Gravity's acceleration is a constant force that pulls objects towards the center of the Earth. It is measured as 9.8 meters per second squared.

2. How does gravity's acceleration affect objects?

Gravity's acceleration causes objects to fall towards the ground with increasing speed. The force of gravity also affects the weight of an object, making it feel heavier.

3. Does gravity's acceleration change on different planets?

Yes, gravity's acceleration is different on different planets. It is dependent on the mass and size of the planet. For example, the gravity's acceleration on Mars is about one-third of that on Earth.

4. Can gravity's acceleration be measured?

Yes, gravity's acceleration can be measured using a device called an accelerometer. This device measures the rate of change of an object's velocity and can calculate the acceleration due to gravity.

5. How does air resistance affect gravity's acceleration?

Air resistance can affect the acceleration of an object due to gravity. As an object falls, air resistance creates an opposing force, which can slow down the object's acceleration. This is why objects with a larger surface area, such as a feather, fall slower than objects with a smaller surface area, such as a rock.

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