It is the force of attraction that causes physical things to move towards each other and to fall towards the Earth. Gravity keeps Earth and all the planets in our solar system in orbit around the Sun. Gravity also keeps the Moon in orbit around the Earth. Without gravity, we would be floating around like astronauts in space!
All objects in our universe containing mass are exerting a gravitational force on other mass. If an object is small, the gravitational pull is smaller. If an object is large (like the Earth and Moon), the gravitational pull is enormous. So how is the Moon staying up there in the sky?
Since there is a force of attraction toward the Earth, it’s as if the moon “falls” into an orbit around the Earth and revolves around us. The gravity of the Earth that is holding us down is also keeping the Moon in orbit. Otherwise the Moon would just travel in a straight line.
A common playground game that children play is called tether ball. A volleyball is attached to a rope, or tether. That rope is attached to a metal pole and a stationary base. Each player’s objective is to hit the ball one way. The winner of the game is the player who winds the ball all the way around the pole down to the rope. What does this have to do with gravity, you ask? Well, if the volleyball becomes detached from the rope, the ball would sail through the air in a straight line, losing gravity. However, while the ball is attached, the string is being pulled towards the player’s hand much like the gravitational pull of the Earth.
Connections content provided by April Cox, 5th grade teacher at Jo Byrns Elementary School in Robertson County, Tennessee
G-force?
- G-force is the measurement of acceleration (speeding up) forces.
- 1-g is the force of Earth’s gravity and determines how much we weigh.
- At 5-gs, a race car driver experiences a force equal to five times his weight.
- Race car drivers can experience over 100-gs if they have a crash that causes them to decelerate (slow down) quickly over a short distance.
- Some roller coasters have been known to include G-forces of around 4 to 6-g.
- People can experience increasing G-forces also, such as those who participate in airplane acrobatics and space training.
- John Stapp was called a G-force pioneer because he experienced the highest known acceleration by a human at 46.2-g. As part of a test program, he rode a rocket sled that was designed to measure the effects of deceleration on the human body. Why did he do this? He wanted to help improve the aircraft design by better protecting passengers and pilots.
What Are Tides?
Tides are the regular upward and downward movement of the level of the ocean that is caused by the pull of the Sun and the Moon on the Earth. Because the gravity of the Moon pulls on the Earth, the tides rise and fall daily. The sea level swells in waves when the Moon passes over the ocean. There are low tides and high tides daily, with constant movement. If you’ve ever been to the ocean, you may have seen flags that are used to explain conditions of the
water. The red flag describes when the tidal current (horizontal or sideways flow of water) is the strongest and when there are the most serious conditions in the water because of the up-and-down tidal movement. When the tide is rising, it is called flooding current. When the tide is falling, it is called ebbing current. There are times when there is no ebbing or flooding. This is called slack water.
Did You Know…
Isaac Newton’s theory of gravity was inspired by seeing an apple fall from a tree.
Albert Einstein’s general theory of relativity is used to describe gravity.
Sources: www.physics4kids.com/files/motion_gravity.html, www.sciencekids.co.nz/sciencefacts/gravity.html,
www.boatsafe.com/kids/tides.htm, www.merriam-webster.com/dictionary/gravity, www.rocketcityspacepioneers.com/space/rocket-sled
