# Simple Question on Earth Rotation involving Newton III

• Jaygo333
In summary: The net force on the pendulum is zero and it will continue swinging back and forth at the same rate.If an object is moving in a straight line at a constant velocity, what's the force that keeps it balanced? Momentum is what keeps an object moving in a straight line at a constant velocity.

#### Jaygo333

Simple question with a simple answer, just want a little more description.

Newton III states: For every action there is an equal and opposite reaction.

As the Earth rotates one way, what's the opposite force that keeps it "balanced"? Inertia?

Arrived at the question when was thinking about a pendulum in SHM but could not
figure out why if, in a perfect system, why it kept coming back to the same position with the Earth rotating only one way? Rationally thought there would be an over swing in the direction the Earth was rotating. But Newton III states there must be a force acting on opposite end and after much thought, still stumped.

No force is needed to keep the Earth rotating (remember Newton's 1st law) if you wanted to change the rotation then you would need something for the force to act against

If an object is moving in a straight line at a constant velocity, what's the force that keeps it balanced?

It takes a force to change an object's motion. Regardless of whether it's moving in a straight line or rotating, momentum keeps it moving at the same rate, while a force changes that motion.

Just as you have conservation of linear momentum, you also have conservation of angular momentum.

Assume the Earth is rotating left. Now, when watching a pendulum, swing left and right, shouldn't it swing farther left because the sum of all its forces, including the Earth's rotation would be greater that way than the sum of all its forces in the right direction because the Earth's rotation is missing in the equation?Thanks for that response BobG. You posted when I was in the middle of writing this.

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Jaygo333 said:
Newton III states: For every action there is an equal and opposite reaction.
Newton III applies to forces.

As the Earth rotates one way, what's the opposite force that keeps it "balanced"? Inertia?
Rotation is not a force.

Arrived at the question when was thinking about a pendulum in SHM but could not
figure out why if, in a perfect system, why it kept coming back to the same position with the Earth rotating only one way? Rationally thought there would be an over swing in the direction the Earth was rotating. But Newton III states there must be a force acting on opposite end and after much thought, still stumped.
For a pendulum swinging back and forth, there are forces involved and thus Newton III applies. The result is that as the pendulum bob moves to the left of equilibrium, the support (and attached earth) moves ever so slightly to the right of equilibrium.

## 1. What is Newton's Third Law of Motion?

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object will exert an equal force in the opposite direction on the first object.

## 2. How does Newton's Third Law apply to Earth's rotation?

Newton's Third Law applies to Earth's rotation because the rotation of the Earth is caused by the gravitational force between the Earth and the sun. According to Newton's Third Law, the Earth exerts an equal and opposite force on the sun, causing the Earth to rotate around its axis.

## 3. Why does the Earth rotate from west to east?

The Earth rotates from west to east because of its initial angular momentum. When the solar system was formed, the gravitational pull of the sun caused the planets to rotate in the same direction as the sun's rotation, which is from west to east.

## 4. How does the conservation of angular momentum relate to Earth's rotation?

The conservation of angular momentum explains why the Earth continues to rotate at a constant speed. This law states that the total angular momentum of a system remains constant unless acted upon by an external torque. Since there is no external torque acting on the Earth, its rotation remains constant.

## 5. Does Earth's rotation affect the tides?

Yes, Earth's rotation does affect the tides. As the Earth rotates, the water on the surface is pulled towards the equator due to centrifugal force. This causes a bulge of water, creating high tide. As the Earth rotates away from the moon, the bulge of water moves towards the poles, creating low tide. This effect is known as the Coriolis effect.