# Eight minutes, an ordinary topic

#### neila9876

In Woody's leaning tower experiment, there are two kinds of interaction:
1. The interaction of gravity between the iron ball and the Earth. It is there long long ago;
2. The interaction of tension between Woody and the iron ball.
As soon as Woody let go of the bungee chord, the interaction of tension between Woody and the iron ball disappears. The interaction of gravity between the iron ball and the Earth demonstrates itself immediately.

#### benit13

In Woody's leaning tower experiment, there are two kinds of interaction:
1. The interaction of gravity between the iron ball and the Earth. It is there long long ago;
2. The interaction of tension between Woody and the iron ball.
As soon as Woody let go of the bungee chord, the interaction of tension between Woody and the iron ball disappears. The interaction of gravity between the iron ball and the Earth demonstrates itself immediately.
The time taken for a gravitational wave to propagate from the Earth to the iron ball is very, very small (let's call it $$\displaystyle \Delta t$$), so I don't know what you mean when you say that the interaction with gravity was from long, long ago. However, the interaction of gravity is continuously happening, so as soon as Woody let's go of the cord, the gravitational wave emitted at the time equal to the present time $$\displaystyle - \Delta t$$ will interact with the ball, causing it to drop.

Think of it like this... when a light bulb is turned on, the light is continuously shining. However, at any given moment, the light hitting you is light that was emitted from the light bulb at some very small time $$\displaystyle \Delta t$$ before it hit you. Since this light is the light you are using to understand what the light bulb looks like, the light bulb appears as if it were $$\displaystyle \Delta t$$ younger than the present time. If the light bulb changed colour, it would take $$\displaystyle \Delta t$$ seconds before you notice it. The same is true with all of the interaction mechanisms (gravity, electromagnetic, strong nuclear and weak nuclear).