force (force and motion) (teach)

Force and

MotionForce is a push or a pull

By Moira Whitehouse PhD

The strength of a force can be measured. How strong the push or pull is measured with a spring scale in units called newtons.

One newton is equal to about a quarter of a pound.

This is a newton scale. By hooking itonto an object and pulling it along, one can read the force that is required to move that object under those conditions.

There are four kinds of forces; some scientists also add the fifth, friction.

Weak nuclear force:

Strong nuclear force:

Electromagnetic force:

Gravitational force:

Short-range force responsible for binding atomic nuclei together. The strongest of the four fundamental forces of nature. Important force in certain decaying functions within the atom, but way beyond me.

a force between objects exerted by positively and negatively charged particles.

the force of attraction between all masses in the universe; especially the attraction of the earth's mass for bodies near it.

Electromagnetic force

We know that everything is made up of tiny particles called atoms.

Although atoms are much too small to be seen, scientists have figured out that they are made of even smaller particles that have electrical charges. They are called protons and electrons.

Let’s start with....

Protons and electronsEverything is made up of atoms and every atom is made up of protons in the nucleus with positive electrical charge (+) and electrons swirling around the nucleus each with a negative electrical charge (-). There are also neutrons in the nucleus but they have no electrical charge.

http://www.windows.ucar.edu/

Because atoms have the same number of positive (+) and negative (-) charges, most things are in electrical balance.

But when the atoms of an object get out of balance electrically, strange things happen.

They can get out of balance when the swirling negatively charged electrons are knocked loose from their atom. This can happen rather easily and helps explain static electricity.

Sometimes when two electrically balanced objects rub against each other, electrons from the one are rubbed off onto the other. The object that received the electrons would then have extra electrons and an overall negative charge.

The object that lost the electrons would no longer be balanced having too many protons for the remaining electrons and thus becoming positively charged.

Even though we say that “strange things” happen depending on the balance or unbalance status of the electrons, the reactions are actually very predictable.

If the both objects have excess negative charges:If the both objects have excess positive charges:

Like charges repel

If the objects are balanced:

Uncharged

If one object has positive and the other has negative excesses:

Opposite charges attract

Shoes and carpet, like most everything else, are made of atoms that are electrically balanced. But when shoes rub against the carpet, electrons are transferred from the carpet to the shoes and the shoes become negatively charged.The carpet which loses electrons to the shoes becomes positively charged.

As you proceed about your business with all those extra electrons, you do not notice anything until......you touch a metal doorknob?

Those electrons that moved up from your

shoes are now ready to

get “in balance” again.

The metal doorknob which is a good conductor

of electricity, is neither positively or negatively charged.

When your negatively charged finger approaches the metal doorknob the attraction becomes greater until...

ZAP!!!

You may have noticed that you do not build up static electricity when you walk across a concrete floor. That is because some atoms hold on to their electrons more tightly than others do.

Examples of materials that are more apt to give up electrons are: fur, glass, human hair, nylon, wool, silk.

Examples of materials that are more apt to capture electrons are: styrofoam, Saran Wrap, polyurethane polyethylene (like Scotch Tape) polypropylene vinyl (PVC).

Or, negative clothes are attracted to the positive clothes.

Often when you take clothes from the clothes dryer, they seem to stick together.This is because some of the clothes have gained electrons by rubbing against other clothing. The clothes losing electrons become positive and are then attracting those pieces of clothing that have gained extra electrons.

Objects with extra (+) charges push away away from each other.

Objects with extra (-) charges push away away from each other.

Objects with + and – charges attract one another.

The bottom line, once again:

It’s like the poles of a magnet, “likes repel and opposites attract.”

Now we will do an experiment to demonstrate what we have been discussing.

B

Here we have two pieces of tape with the ends wrapped around tooth picks.

These two pieces of tape are marked with a “B” to show that they are on the bottom and sticking to the surface.

B

Next we will stick two more pieces of tape on top of the first two. They are marked with a “T” for top.

T

B

T

B

Using your materials, set up the experiment by sticking (pressing) your “T” tape directly over the (on top of) the “B” tape while it is still sticking to the surface of your table.

Now peel the top tapes off. They both had electrons stripped away when they were peeled up.

So now the “T” tapes will have fewer electrons because of those they lost, but the same number of protons they started with, which makes them positively (+) charged.

T

B

T

B

Now you are going to “test” your two “T” pieces of tape by holding them close to each other to see if they repel or attract. Before you do, make a prediction. Next, peel up the “B” pieces of tape from your table and after making your prediction, test them in the same way.

Finally, test one of the “B” pieces of tape with one of the “T” pieces, but only after making a prediction whether they will repel or attract.

Another vivid demonstration of what happens when the electric balance of an object is upset is the Van de Graff generator.

The Van De Graff generator is a device that demonstrates the effects of unbalanced charges as can be clearly seenhere.

Van de Graff generators have several parts: a motor, a belt, two rollers, two "combs," and a metal sphere.

The bottom roller is made out of a material that loses electrons easily, and the upper out of a substances that readily captures electrons.A comb pulls electrons from the material on the bottom roller (which loses electrons easily) and transfers them to the rubber belt.

As the motor turns, the rubber belt first goes over the bottom roller.

The belt then travels to the top roller. The second comb

near the top roller collects the electrons from the belt and stores them on the metal sphere. The motor turns very fast, so the sphere quickly collects a lot of electrons and becomes negatively charged and so do you when you touch the dome.

Touching a charged sphere is truly a "shocking" experience!

When a person places their hand on the ball and the machine is turned on, electrons are transferred to and collected on the person touching the silver ball.

Why do you think this machine affects the hair of the children in the picture?

Magnetism and electricity are related.

If you run electricity through a wire, a magnetic field is set up around the wire-- the wire becomes a magnet as long as electrons flow through it.

Activity with circuit and compass.

An electromagnet is a magnet that runs on electricity.An electromagnet works because an electric current produces a magnetic field. Unlike a permanent magnet, the strength of an electromagnet can easily be changed by changing the amount of electric current that flows through it. The poles of an electromagnet can be reversed by reversing the flow of electricity. If a wire carrying an electric current is formed into a series of loops, the magnetic field can be concentrated within the loops. The magnetic field can be strengthened even more by wrapping the wire around a core of soft iron.

This business of an electric current running through a coil of wire and making a magnet opens all sorts of possibilities, like electric motors and electric generators.

Any electric motor is all about magnets and magnetism. A motor uses magnets to create motion.

We will use this simple Beakman motor for study. The armature or rotor (in this case the coil of copper wire) is an electromagnet.

The ends of the copper wire in the coil make contact with the pieces connected to the battery terminals.Current flows through the coil, making it into an electromagnet.

Inertia causes the coil to continue around and when the coil nearly completes a spin, the process repeats itself.

Since magnets attract, the coil is attracted to one pole of the ceramic magnet.

Activity with electric motors

We have just seen how electricity is used to make motion, now we’ll see how motion is used to make electricity.

It uses motion to generate electricity.

This is a generator.

www.energyquest.ca.gov

A generator has a long, coiled wire on a shaft surrounded by a giant magnet.

When the turbine turns, the shaft and rotor also turn.

As the shaft inside the generator turns, an electric current is produced in the wire. An electric generator converts mechanical, moving energy into electrical energy.

The generator is based on the principle of "electromagnetic induction" discovered by Michael Faraday, a British scientist in 1831 Mr. Faraday discovered that if an electric conductor, like a copper wire, is moved through a magnetic field, an electric current will flow in the conductors.

Consider the many things that we depend on daily that are powered by electricity, and then realize our debt to its discoverer. His name is Michael Faraday.

Activity with generator