Today’s Wonder of the Day was inspired by Mia. Mia Wonders, “How does Gravity keep us on the ground?” Thanks for WONDERing with us, Mia!
If you hold an egg between your fingers and then release it, what will happen? Will it float up to the ceiling? Of course not! It’ll fall to the ground and probably crack open. Why? That’s right. It’s all due to a little force we call gravity.
Thanks to gravity, we have our feet firmly on the ground. Without gravity, we might float right into outer space. Instead, Earth pulls us toward its center at all times, keeping us on the ground.
Every object with mass has a gravitational pull on everything around it. That force depends on the masses of the objects. Things with a lot of mass, such as Earth, exert a strong gravitational pull on the objects near them, such as people and animals.
In addition to pulling other things toward it, Earth also accelerates those objects as they get closer to the ground. In other words, items speed up as they approach Earth. More importantly, the laws of science tell us that all objects—regardless of their mass—gain velocity at the same rate as they fall.
Italian scientist Galileo Galilei calculated the rate at which objects fall. According to his calculations, an object that is dropped falls to the ground at a rate of 9.8 meters per second, squared.
But how can that be? It seems counterintuitive based on our experience with the world around us. For example, if you hold a feather in one hand and a brick in the other and drop them at the same time, they won’t hit the ground at the same time. Will they?
Which will hit first? If you said the brick, you’re right! But why is that? If gravity causes objects to fall toward Earth at the same rate, then why will the brick hit the ground long before the feather?
The answer lies in another scientific concept: air resistance. Air is all around us. Those air molecules push against each other and against other objects. They provide an upward force of friction against anything that is falling. Galileo also discovered that the more dense something is, the less it’s affected by air resistance. Objects that are less dense will be slowed down more by air resistance.
This explains why a feather will fall to the ground very slowly when dropped. On the other hand, a brick will fall quickly—as if there was no air around it. Scientists who have tested these theories will tell you that, if you drop a feather in a vacuum (a container with no air), it will fall at the same rate as the brick!
Isn’t that fascinating? Think about the last time you dropped something. Was it a piece of paper? A set of keys? A tennis ball? Air resistance would have a different effect on each of these items. Which one do you think would fall the fastest?
Standards: NGSS.PS2.A, NGSS.PS2.B, NGSS.PS3.C, CCRA.L.3, CCRA.L.6, CCRA.R.1, CCRA.R.2, CCRA.R.4, CCRA.R.10, CCRA.SL.1