# How does gravity convert potential energy to kinetic?

• sayetsu
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.

#### sayetsu

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?

Delta2
Energy is converted or transferred by work. This is a force (gravity) applied over a distance (falling).

russ_watters
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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Lnewqban and anorlunda

## 1. How does gravity convert potential energy to kinetic?

Gravity converts potential energy to kinetic energy by pulling objects towards the Earth's surface, causing them to accelerate. As an object falls, its potential energy decreases and its kinetic energy increases.

## 2. What is potential energy in relation to gravity?

Potential energy is the energy an object has due to its position or state. In relation to gravity, potential energy is the energy an object has due to its position in a gravitational field.

## 3. How is kinetic energy affected by gravity?

Kinetic energy is affected by gravity because it is the force of gravity that causes objects to accelerate and gain kinetic energy. The greater the force of gravity, the more potential energy an object has, and the faster it will accelerate and gain kinetic energy.

## 4. What is the formula for calculating the conversion of potential energy to kinetic energy?

The formula for calculating the conversion of potential energy to kinetic energy is:

Kinetic Energy = Mass x Acceleration due to gravity x Height

## 5. How does gravity affect the speed of an object as it falls?

Gravity affects the speed of an object as it falls by increasing its velocity as it falls towards the Earth's surface. As the object gets closer to the ground, the force of gravity becomes stronger and the object's speed increases.