Every object on Earth is held together by at least one of the four fundamental forces of nature: the strong force, the weak force, the electromagnetic force, and gravitation. These four forces are found within all atoms, and they dictate the interactions between individual particles and the large-scale behavior of all matter throughout the universe. Since the first two forces (strong and weak) require the use of a nuclear power plant, we’ll focus on the other two forces (electromagnetic and gravitation).

Gravitation is the force that is always attractive (never repels or pushes away). This is the force that pulls matter together and keeps your feet stuck to the sidewalk. Gravitation causes comets to be slung through our solar system, binds the moon in its orbit around the Earth, and is the sworn enemy of major league baseball pitchers everywhere.

The reason you get a shock by scuffing along the carpet can be explained in the realm of the electromagnetic force. This force determines how electrically charged particles interact and is either attractive or repulsive. Identical charges repel each other (two positive or two negative charges). Electromagnetic force is the source of power used in blenders, dishwashers, aircraft engines, solar flares, and lasers—and is a culprit in bad hair days worldwide.

The conservation of energy is the idea that “you get out what you put in.” When you fuel your vehicle with gas or electricity, that energy is converted into work you can see (e.g., the car cruising down the road), as well as things you may not notice (heat from the engine, headlights, sound energy, recharging your electrical battery, and so on).

We use complicated machines such as a car’s engine to convert energy from gasoline into work, but there are many simpler ways we can see energy at work. Machines don’t need to be as complex as the internal combustion engine—chances are you use several simple machines every day in your home.

Simple machines make our lives easier. They make it easier to lift, move, and build things. You probably use them more often than you think. If you have ever screwed in a light bulb, put the lid on a jam jar, put keys on a keychain, pierced food with a fork, walked up a ramp, or propped open a door, you’ve made good use of simple machines.

Simple machines use mechanical advantage to do certain things more easily (or do things that you would not be able to do at all). Mechanical advantage is like using brains instead of brawn (like using your mind instead of just muscular strength). With pulleys and levers, you use your “mechanical advantage” to leverage your strength and lift more than you normally could handle, but it comes at a price: you trade force for distance. When you use our pulley system (described later), you can thread it up to lift ten people with one hand, but here’s the trade-off: you will have to pull 10 feet of rope for every 1 foot they rise. To figure out the mechanical advantage in a pulley system, count the number of strings in your system. If there are seven strings, you can pull with seven times your normal strength.

With levers, it’s a little easier to figure out the advantage, mostly because there are no strings to count or get tangled up because you are using fulcrums (picture the pivot point in a see-saw). By moving the fulcrum of a lever around, you can dramatically change the amount of weight you can lift. Let’s put these ideas to work and start doing science activities!

Science Activity: Exponential Friction

Find a smooth, cylindrical support column, such as those used to support open-air roofs for breezeways and outdoor hallways. Wind a length of rope one time around the column and pull on one end while three siblings or friends pull on the other end in a tug-of-war fashion. Experiment with the number of friends and the number of winds around the column.