Gravity's Role in the Universe: Tutorial

The mass of an object is 45 kilograms. Its weight on Earth is __newtons, and its weight on the Moon is __newtons.

441 and 72

What would happen to the Moon and Earth if the Sun did not exist?

As far as the Earth goes, we wouldn't be able to stay alive because the sun helps us produce food like crops for farming, and we would be living in the dark. As far as the moon goes, there isn't any life and its already naturally dark and there is no atmosphere. So for Earth no life would survive without the sun.

When you step on a bathroom scale, it tells you how much you weigh. How is the word weight defined? If you're not sure, take a guess. A)the amount of matter in an object B)a measure of the pull of gravity on an object C)the speed at which an object strikes Earth D)the distance between an object and Earth

B)a measure of the pull of gravity on an object

Scientists have explored only a small portion of space. What evidence is there that gravity exists outside of what they have explored?

Gravity is the force that holds our Solar System together. It allows planets and moons to keep their elliptical orbits around the Sun. Even though humans have explored only a small portion of space, we know that our Solar System orbits the center of the much larger Milky Way galaxy. Without gravity, our Solar System would not be able to maintain this orbit.

Pluto, the dwarf planet, is 5.9 billion kilometers from the Sun. Explain how a model showing the gravitational pull on Pluto would differ from your model of Earth's orbit.

The distance between the Sun and Earth is 149,600,000 kilometers, and the distance between the Sun and Pluto is 5.9 billion kilometers. The gravitational pull decreases with an increase in distance. So, the gravitational pull of the Sun on Pluto is much less than its pull on Earth. So, in the model, Pluto's orbit would have a much larger radius than Earth's orbit.

In your model, how does mass affect the gravitational pull of the Sun, Earth, and the Moon? How do their masses explain their orbits?

There's a gravitational pull between each pair of celestial bodies. The pull increases with the mass of the objects. The Sun's mass is 1.989 × 1030 kilograms, and Earth's mass is 5.9726 × 1024 kilograms. The Sun has more mass than Earth, so the force between them draws the smaller Earth toward the Sun. This makes Earth go around the Sun. The mass of Earth is 5.9726 × 1024 kilograms, and the mass of the Moon is 7.3477 × 1022 kilograms. Earth has more mass than the Moon, so the force between them draws the smaller Moon toward Earth. This makes the Moon go around Earth. The Sun keeps Earth in orbit, and Earth keeps the Moon in orbit.

Explain how this simulation relates to Earth's gravity as it orbits the Sun.

We can compare Earth and the Sun to the two balls in the simulation. Earth has a lot of mass, but the Sun has much more. The gravitational pull between them is very strong. Earth is in constant motion, but the heavier Sun pulls Earth toward it. This tug-of-war between the two spheres helps Earth remain in its near-circular orbit. If the Sun did not exert this pull, Earth would veer away from its orbit.

Keeping the mass of the balls equal, decrease the distance between them. What happens to the force arrows?

When the distance between the balls decreases, the size of the arrows increases. This shows that the gravitational pull between the balls also increases.

Now, set the mass of both balls to be equal. Increase the distance between them by pulling one of the balls away from the other. To pull a ball away, click on the ball and drag it. What happens to the force arrows between the two balls? What does this mean in terms of gravity?

When the distance between the balls increases, the size of the arrows decreases. This shows that the gravitational pull between the balls also decreases.

What happens to the force arrows when you decrease the mass of the balls? What does this mean?

When the mass of the balls decreases, the size of the arrows decreases. This shows that the gravitational pull between the balls also decreases.

Increase the mass of each ball either by using the pointers or the slider in the Mass 1 and Mass 2 boxes. Now, look at the arrows. What happens to the force arrows above each ball when you increase the mass of the balls? What does this mean in terms of gravity?

When the mass of the balls increases, the size of the force arrows increases. This shows that the gravitational pull between these objects also increases.

Three-year-old Ben and his father are playing with a ball at the park. Ben's father throws a ball high up into the air. Ben thinks the ball will never come back. His father assures him that the ball will always come back. What made Ben's father so sure that the ball would fall back to Earth?

When you throw a ball into the air, it always comes down if nothing gets in its way. Earth's gravity pulls on objects that are near Earth's surface. The only way objects can break from Earth's gravity is if they are pulled away by a stronger force.

Why is the gravitational slingshot important to space exploration? to allow spacecraft to refuel without stopping to help spacecraft increase velocity without using additional fuel to make spacecraft weightless to make spacecraft safer

to help spacecraft increase velocity without using additional fuel

Based on your observations in parts A through D, explain why Earth's gravity pulls you toward the ground.

The gravitational pull between two objects increases as the distance between them decreases. The gravitational pull also increases with an increase in the mass of the objects. Earth has a large mass. So, when our bodies are close to Earth, the gravitational pull between us and the Earth is strong. This force pulls us down, so we stand firmly on the ground without floating in the air. Without the gravitational force, we would drift away from Earth.

Consider this statement: Earth is the only source of gravity in the solar system. Do you agree? Give your reasons.

The statement is false. The Sun, Moon, planets, and other objects in the solar system also have a gravitational pull.