A string around the Earth’s equator


Place a string around the Earth’s equator and pull it snug. Add a length of one meter to the string and push it away from the equator an equidistant amount. What is the largest animal, from the list below, that would now be able to walk under the string?

Flea Mouse Dachshund Calf Horse Elephant
Continue reading


A geostationary satellite

Geostationaryjava3DsideviewA geostationary satellite is a satellite in geostationary orbit, with an orbital period the same as the Earth’s rotation period. The geostationary orbit is a circular orbit directly above the Earth’s equator.

How high above the Earth’s surface must the geostationary satellite be placed into orbit?

Continue reading

How long would it take to fall through the center of the Earth?

We have a hole that leads straight through the center of the Earth. We neglect air resistance and assume that the Earth has uniform density ρ. How long would it take to fall through the center of the Earth and reach the other side of the planet?

Continue reading

If the solar system were reduced

Solar System (artist's impression) If all the linear dimensions of the solar system were reduced in some proportion, then what will be the length of Earth’s year?


Continue reading

How long does it take for the Earth to reach the Sun?

If we stopped the Earth in orbit then how long does it take for the Earth to reach the Sun?

Continue reading

Why is the Earth Round?

EarthNasaThe Earth, the Moon, the Sun, the stars and the planets round or spherical, because they have a very large mass. Their own gravitational force aims to give them the shape of a sphere.

Continue reading

 Where does a bullet fall if someone shoots it straight up?

rifleAt the North or South pole a bullet will land at the same spot, but at the equator …
Continue reading