Thursday

Raven lays the NASA Planetary Fact Sheet beside yesterday's Field Log. "Same toss, different world," she says.

Rocket finds the gravity row. "Earth, 9.8. The Moon, 1.6. That is way less pull."

"So what happens to the arc?" Raven asks. "What do you notice about the fall?"

"Gravity pulls less, so the ball falls slower. It stays up longer. It goes farther!" Rocket says, almost shouting.

Nova hovers over the Jupiter column. "And here?"

Rocket reads 23.1 and winces. "The ball would drop fast. Short little arcs."

Raven smiles. "A physics text says an astronaut once hit a ball a long way on the Moon. Now you know why."

NASA publishes a Planetary Fact Sheet with each world's mass and surface gravity. Surface gravity is how fast a dropped object speeds up.

It is given in metres per second squared. A bigger number means a stronger pull and a faster fall.

NASA's flight page gives 9.8 metres per second squared on Earth, and says the value differs on the Moon and Mars.

The standards say gravitational interactions are attractive and depend on the masses of the interacting objects.

The Moon has far less mass than Earth, so its pull at the surface is far weaker: 1.6 compared with 9.8.

A physics text says the range of a projectile also depends on the strength of gravity. Weaker gravity, longer range.

That is why an astronaut on the Moon was able to send a ball a great distance. Gravity is weaker there.

Your own Field data is the Earth row. Everything you measured yesterday happened under a pull of 9.8.

Excellent data reading. Tomorrow you take arcs to the pitch, the court and the long jump pit.