Gravity

Physics 1: Gravity

Time needed for this session: about 20 minutes.
Things needed: small objects of different sizes to illustrate your point, but use them only if a concept is not being understood.  Most boys are very visual, so an object often has the upside of teaching a concept better. But boys get distracted very easily, so taking an object out is a guaranteed distraction. Thus, it is best that you handle the objects and put them away and out of sight when not using them.

I used two small magnets of the same strength, two balls of different sizes, tiny "dot" stickers, and legos. I pre-sorted the legos into two colors, about two 1x1 bricks of each color, and one 4x2 bricks of three different colors, including two of the same color that you used for the 1x1s.

Parents' note: 

Let's teach our sons about physics at an age appropriate level. Let him ask questions and really understand the topic. You might have to explain the same topic, but using different examples.  In this blog, I retouch on the same topics, which to an adult is redundant. But once you do this and you see the concept sink in and the delight spread across your son's face - this will all be worth it. And later, you will have to review previous topics because he will forget the concepts; these topics are all related to each other so, this takes time.  I took the time to do this and it turned my son onto science, where he quickly went then went through the Science belt loop, Science pin, Nova, and SuperNova award.

So let's learn about gravity by learning about mass.  We will then learn about Density, which is related to mass and volume, which leads to Galileo's experiment, which involves mass and inertia, which leads to aerodynamics and friction.  This module should last about 20 minutes. Obviously, you can do more modules if your son has the patience. Or if your son is like mine, it ends up in an hour long cascade of questions where, before you know it, you discussing how autotune works or why France makes good cheese.

I will put an asterisk behind things that I know are generalizations and simplifications. We're not teaching University level stuff here. These are 6-10 year old boys who are just learning this stuff.

For your son:

Science is the study and knowledge of how things work. At school, you learn science. So you learn science to learn how and why things work.

There is a science for everything. The science of numbers and how they work together is math. The science of motion is "physics". So we are going to learn a bit about physics to learn about how motion works to make your Pinewood Derby car go faster.

Gravity

What is gravity?

You know that every time you jump, you come back down. But what is "down"? The earth is round. People on the other side of the earth also come back to earth and they are upside down compared to you.  Gravity pulls us all toward Earth. So how come we all jump in different directions and all come back toward the earth and not up and into outer space?

Force

Gravity is the "force" in nature having to do with "mass". What's force? A force is like unit of motion*. You use your muscles to generate force - like when you jump, you have upward force motion. Magnets push and pull toward each other with a specific force. You can feel that force. Some have more magnetic force than others and you can feel the strength of them as they pull and push each other. (Give magnets for a short period and then take back)

Mass

Gravity is a force in nature where all things are pulled toward each other depending on their "mass".  So what is mass? Mass is a measure of how much stuff is in something.

Basic Chemistry

(Parents' note: this may be a bit complicated for some kids, so you can skip over Chemistry section if you think your son isn't ready for this yet).

Everything is made out of basic building blocks of the universe called neutrons, protons, and electrons. Protons and electrons are literally tiny magnets. Protons have a positive charge and electrons have a negative charge. The protons and electrons pull toward each other and click together.  (Use the magnets to illustrate). The neutrons have no charge, but they often get sandwiched in between the protons and electrons. Once the protons, electrons, and neutrons click together, the magnetic forces cancel each other out and they stick together*.

Each one of these tiny sandwiches is an "atom".  (This is where I take out the legos and sticker dot to illustrate the point.)

A proton (1x1 brick of color A) has a positive charge. An electron (a sticker dot) has a negative charge. These electrons are really tiny compared to the proton*.  The proton and electron are attracted to each other and form an atom (stick the sticker on top of the brick). They are stuck to each other and it is now an atom. This is atom with one proton, one electron, and no neutrons.  It is a hydrogen atom. (Make another 1x1 brick and sticker that is identical to the first).  Here is another hydrogen atom.  This is what the sun is mostly made of.

(Take out the 2x4 bricks). Here is a group of eight protons (count the nobs on the top and/or compared to the 1x1 brick).  It gets attracted to eight electrons (hold up the stickers). But a group of eight neutrons gets sandwiched in between.  (Put the "neutron" 2x4 bricks on top of the "proton" 2x4 brick, then stick the eight stickers on top of the neutrons).  This atom is oxygen. It is a different atom than hydrogen.

So far, we have found 115 different types of these atoms*.  There is one atom with one proton, which you already know as hydrogen. There is one with two protons. There is one with three and so forth all the way up to 115*. And everything in the universe is made up of these 115 different atoms*.

Sometimes atoms interact with each other in different ways and combine to form new materials. When you combine these two hydrogen atoms with the oxygen. This is is water. This is why it is also called "H20". Two Hs. One O.

Mass is measures how much stuff is in it.  And by stuff, we mean protons, neutrons, and electrons. Protons and neutrons are about the same mass.  They are measured in atomic weight.  Look at this water molecule. See the hydrogen atom? It has one proton. The electron is so tiny compared to the proton that it has almost nothing*.  This hydrogen atom has an atomic mass of 1*.  So does the other hydrogen molecule.  It has an atomic mass of one.  The oxygen atom has eight protons and eight neutrons. (count out the protons and neutrons together).  The oxygen has an atomic mass of 16.  The 16 mass and the two single atomic masses from the hydrogen means that water molecule has an atomic mass of 18*.    

Weight

Mass is not the same as weight, but they are directly related to each other. Weight is how we measure mass, but weight depends upon where you are.  Remember how gravity is the force that pulls things together depending on how much mass there is?  (Take out the large ball and small ball).  This larger ball has more mass than this one because it has more stuff/atoms in it. You have mass and you are bigger than the ball, so you have a tiny gravitational force pulling them toward you. Now the earth is HUGE compared to us, so it has a gravitational pull that is really big. That is why we get pulled toward it no matter if we are jumping on this side of the planet or the opposite side.


You weigh something on Earth, but you weigh about one-sixth as much on the moon because the moon is made of less stuff.  The moon has less mass than the Earth so you get attracted to it less. Meanwhile, Jupiter has a lot more mass, so it would weigh more on Jupiter because its gravity is so much stronger.

Let's have some fun calculating how much you weigh on other planets in our solar system.
http://www.exploratorium.edu/ronh/weight/


We are doing the Pinewood Derby on earth, so we will be using different materials. We will use wood body, steel axles, plastic wheels, a tiny bit of paint, and weights made of  (insert weight type here).

Your Pinewood Derby car (if your rules are standard) can only weigh up to 5 ounces total.  And since we will remain on planet earth, it will remain 5 ounces.

This is very important thing about designing your car. Your car should weigh EXACTLY 5 ounces. If it is less than 5 ounces, you have a big disadvantage because gravity is the only thing  powering your car. All Pinewood cars will be 5 ounces, so having less is a very big disadvantage.

Parents: Have an accurate scale or bring it to the post office if you don't have a scale. I bought a very accurate scale and I use it in the kitchen all the time.

In the next two lessons we will talk about how having less weight is a disadvantage.

Next up: Weight