(Continued from Part 1)

Gregory’s eyes looked back and forth quickly, digesting his fathers questions.

“The moon is in space, circling the Earth every twenty-seven point three (27.3) Earth-days. Think about it. The massive moon is going around and around in a circle. Something is causing this. It’s the gravitational pull between the Earth and the moon.”

Mr. Jackson stood. “Come on, let’s go outside and I’ll explain.”

Gregory laid his pen in the spine of the biology textbook on his desk. “Are you kidding? Since when? Football instead of homework?”

Greg followed the family rocket scientist down the stairs and into the back yard grabbing a cookie as they passed through the kitchen.

“Okay,” Mr. Jackson said, “down with the cookie so we can play catch. You stand over there about ten feet from me.”

“Ten feet? Come on dad, we’ve been throwing twenty yards for years.”

I can’t believe this,” Gregory whispered. “My dad never let’s me play until my homework is done.”

Mr. Jackson stood, facing Gregory, holding the football in the palm of his right hand while slapping it with his left. “Now, what will happen when I toss the football straight up in the air?”

“Well it won’t score any points, that’s for sure.”

Mr. Jackson stood still, holding the football steady, staring at his son.

“Okay, It will come straight down.”

“Now, what will happen when I toss the football up in the air and at the same time toward you?”

“Do it dad.”

Mr. Jackson threw the ball to his son who caught it without struggle. Gregory then threw it back.

“After each throw, take one big step backward.”

Mr. Jackson threw the ball a little harder, a little higher, and Gregory caught it and returned the ball.

“What does the ball do each time I throw it up?”

“It comes back down.”

“But why doesn’t it come straight down?”

“Don’t be silly; cause you are throwing it away from you, to me.”

“That’s right son. Each time I throw the ball vertically, at the same time I throw it horizontally, and the Earth pulls it back down.”

“Keep backing up.”

Mr. Jackson and his son repeated the exercise until  they could throw no farther. They then came together and sat at the back yard picnic bench.

“Now Gregory,” Mr. Jackson said, pointing at a distant hill, “suppose I was standing on top of that hill and had enough strength to throw the ball so hard that is went a hundred miles.”

Again, Gregory raised an eyebrow. “Then my dad wouldn’t be a scientist, or an engineer. You would be a legendary NFL quarterback.”

“Just pretend the football was mounted in a cannon that could accelerate the ball and make it go a hundred miles toward the horizon. What will eventually happen?”

“The ball will eventually fall back to the Earth.”

“Right.” Mr. Jackson stood and got excited. “Now lets imagine a larger cannon or rocket pushing the ball faster and faster, faster than that jet up there,…” Mr. Jackson pointed at a commercial jet passing over with a nice white condensation trail behind.

“But,” Gregory interrupted. “The air will slow the ball down. Even on that jet, without continual thrust, the drag would slow the plane down.”

“Okay.” Mr. Jackson pointed well above the hill. “Imagine the hill, now a mountain that is high enough to extend upward beyond the atmosphere; an imaginary mountain. From there we launch the ball horizontally at a thousand miles per hour. What will happen?”

“The ball will go a great distance until it curves downward and hits the Earth, or the ocean.” Gregory squinted, eyes moved back and forth suddenly. “What’s my dad getting at?”

“Exactly. Now, if we assume we are above the atmosphere of air, and if we launch the ball so fast that it falls toward the Earth at the same rate that the Earth curves downward, then the ball will be in continual free-fall, but it will always miss the Earth. This is called…”

(To be continued)