How does gravity convert potential energy to kinetic?

In summary, potential energy is a shared quantity between two bodies, such as the Earth and a ball held above the ground. When the ball is dropped, work is done by gravity, converting potential energy to kinetic energy in the ball. The potential energy of the Earth-ball system also changes, but is often neglected due to the huge difference in mass between the two bodies. This simplified view can lead to a misunderstanding of energy transfers between kinetic and potential terms.
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sayetsu
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If I hold a ball above the ground, it has potential energy. Once gravity pulls on it, it becomes kinetic. What is gravity and how does it convert one kind of energy to another?
 
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Energy is converted or transferred by work. This is a force (gravity) applied over a distance (falling).
 
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sayetsu said:
If I hold a ball above the ground, it has potential energy.
That's a common misconception often asserted in textbooks and websites. Here is the correct way to see it.
Potential energy is a shared quantity and it takes two to "have" it. When you hold a ball above ground, the two-body Earth-ball system has gravitational potential energy. Now you can choose your system any way you please. Specifically, if you choose just the ball as your system and you drop it, then the Earth does work on the ball which acquires kinetic energy. Because the position of the ball changes relative to the Earth, the potential energy of the Earth-ball system will also change. Mechanical energy conservation requires that the sum of energy changes be zero:$$\Delta K_{\text{ball}}+\Delta K_{\text{Earth}}+\Delta U_{\text{grav.}}=0.$$Now if you drop the ball, the Earth's gain in kinetic energy is very small relative to the ball's because the Earth's mass is so huge that its acceleration is about 10-24 times the acceleration of the ball. Thus, people omit the ##\Delta K_{\text{Earth}}## term from the equation and simplify the picture by saying that the ball "has" all the mechanical energy there is and shares nothing with the Earth. It's a simpler picture but distorts how people think of energy transfers between kinetic and potential terms.
 
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FAQ: How does gravity convert potential energy to kinetic?

1. How does gravity convert potential energy to kinetic?

Gravity converts potential energy to kinetic energy by pulling objects towards the center of the Earth. As an object falls, its potential energy decreases and its kinetic energy increases. This is due to the force of gravity accelerating the object towards the Earth's surface.

2. What is potential energy?

Potential energy is the energy an object has due to its position or state. In the case of gravity, potential energy is the energy an object has due to its height above the ground.

3. What is kinetic energy?

Kinetic energy is the energy an object has due to its motion. In the case of gravity, kinetic energy is the energy an object has as it falls towards the Earth's surface.

4. How is potential energy calculated in relation to gravity?

Potential energy due to gravity is calculated using the formula PE = mgh, where m is the mass of the object, g is the acceleration due to gravity, and h is the height of the object above the ground.

5. How does the conversion of potential energy to kinetic energy affect an object?

The conversion of potential energy to kinetic energy causes an object to accelerate towards the Earth's surface. As the object falls, its potential energy decreases and its kinetic energy increases, resulting in a faster descent.

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