Workshop 7 Web Highlights "Magnetism" As early as 800 A.D., people knew that certain naturally occurring rocks, which they called lodestones, attracted pieces of iron. They knew that needles could be made into magnets by stroking them against lodestones, and that the needle would point North-South. There was not much scientific study of magnetism until about 400 years later. After scientists learned how to tap sources of electricity, other scientists realized that electricity and magnetism were related. Both the permanent magnets the students used in Workshop 6 and the electromagnets created here in Workshop 7 behave the way they do as a result of moving electric charges. In permanent magnets, the charge comes from the spin of electrons in small regions of the magnet called domains, while in electromagnets the electrons move through the wires wrapped around an iron core (in this case a nail). Both types of magnets can provide a force to attract objects, but the force can be "turned off" in the electromagnet by breaking the electrical circuit. "All Objects Fall at the Same Rate" Mass is a physical property: the amount of matter in an object. We measure mass on a balance in units of grams or kilograms. Unlike all other physical units of measure, the kilogram is based on an actual object, a small cylinder of a platinum-iridium alloy kept at the International Bureau of Weights and Measures in France. Inertia is a concept. It is the tendency of an object to remain at rest or to keep moving at constant speed in a straight line. Newton stated: "Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon." This maxim, Newton's First Law of Motion, is sometimes called the Law of Inertia. Mass is a measure of the object's inertia: the greater the mass, the greater the object's tendency to resist change in motion. "Automobile Physics" As our hosts Sallie and Katy pointed out, we experience the effects of Newton's Laws whenever we drive, or ride as in a passenger, in a car. Even blindfolded we could tell when the car is speeding up, slowing down or making a turn. On a bike, if we are moving quickly, we can feel the force of the air pushing against our body. When traveling much faster in a car or plane, the passenger compartment protects us from that force, and it is sometimes hard to tell if it is moving at all. Without any acceleration, it is really difficult for us to sense motion. We should always protect ourselves with a helmet when riding a bike or motorcycle. Today, the vehicles we drive have several devices to keep us safe in a crash. The crumple zone, the seat belts and air bags all work together to increase the time to bring us to rest and spread the forces involved over a larger area of our bodies. For more on airbags: