Why does the speed of a planet decrease as it moves away from the sun?
The speed of a planet decreases as it moves away from the sun due to the conservation of angular momentum. Angular momentum is the product of an object's mass, velocity, and its distance from the axis of rotation. In the case of a planet orbiting the sun, it experiences a gravitational force that causes it to follow a curved path.
As a planet moves away from the sun, its distance from the axis of rotation increases. To maintain conservation of angular momentum, the planet's velocity must decrease because the product of its mass and distance from the axis must remain constant.
This means that as a planet moves further away from the sun, the gravitational force acting on it decreases, causing its velocity to decrease. The decrease in velocity leads to a slower orbital speed, resulting in a longer orbital period.
The speed of a planet decreases as it moves away from the sun due to the principle of conservation of angular momentum. This principle states that the angular momentum of an object remains constant if no external torques act upon it.
To understand this concept, we need to consider the gravitational force acting between the planet and the sun. The force of gravity between two objects depends on their masses and the distance between them. According to Newton's law of universal gravitation, this force is inversely proportional to the square of the distance between the two objects.
As a planet moves away from the sun, the distance between them increases. Consequently, the gravitational force between the planet and the sun decreases. Since there are no external torques acting on the planet, the conservation of angular momentum dictates that its angular momentum must remain constant.
Angular momentum is the product of an object's moment of inertia and its angular velocity. As the moment of inertia of a planet remains constant (assuming its shape does not change significantly), a decrease in the gravitational force acting on the planet causes a corresponding decrease in its angular velocity (or rotational speed). The planet's speed decreases as it moves away from the sun.
In essence, the decrease in gravitational force as the distance increases results in a decrease in the planet's speed due to the conservation of angular momentum.