Every object exerts gravitational force on every other object. The force depends on how much mass the objects have and on how far apart they are. The force is hard to detect unless at least one of the objects has a lot of mass.
Learning Goal 2
The sun's gravitational pull holds the earth and other planets in their orbits, just as the planets' gravitational pull keeps their moons in orbit around them
Learning Goal 3
Electric currents and magnets can exert a force on each other.
Learning Goal 4
Electrical circuits require a complete loop through which an electrical current can pass.
Learning Goal 5
A charged object can be charged in one of two ways, which we call either positively charged or negatively charged. Two objects that are charged in the same manner exert a force of repulsion on each other, while oppositely charged objects exert a force of attraction on each other.
For Grades: 9-12
Learning Goal 1
Gravitational force is an attraction between masses. The strength of the force is proportional to the masses and weakens rapidly with increasing distance between them.
Learning Goal 2a
Electric forces acting within and between atoms are vastly stronger than the gravitational forces acting between the atoms. At larger scales, gravitational forces accumulate to produce a large and noticeable effect, whereas electric forces tend to cancel each other out.
Learning Goal 2b
At the atomic level, electric forces between electrons and protons in atoms hold molecules together and thus are involved in all chemical reactions.
Learning Goal 2c
Electric forces hold solid and liquid materials together and act between objects when they are in contact—as in sticking or sliding friction.
Learning Goal 3
Most materials have equal numbers of protons and electrons and are therefore electrically neutral. In most cases, a material acquires a negative charge by gaining electrons and acquires a positive charge by losing electrons. Even a tiny imbalance in the number of protons and electrons in an object can produce noticeable electric forces on other objects.
Learning Goal 4ab
In many conducting materials, such as metals, some of the electrons are not firmly held by the nuclei of the atoms that make up the material. In these materials, applied electric forces can cause the electrons to move through the material, producing an electric current. In insulating materials, such as glass, the electrons are held more firmly, making it nearly impossible to produce an electric current in those materials.
Learning Goal 4c
At very low temperatures, some materials become superconductors and offer no resistance to the flow of electrons.
Learning Goal 4d
Semiconducting materials differ greatly in how well they conduct electrons, depending on the exact composition of the material.
Learning Goal 5ab
Magnetic forces are very closely related to electric forces and are thought of as different aspects of a single electromagnetic force. Moving electrically charged objects produces magnetic forces and moving magnets produces electric forces.
Learning Goal 5c
The interplay of electric and magnetic forces is the basis for many modern technologies, including electric motors, generators, and devices that produce or receive electromagnetic waves.
Learning Goal 6
The nuclear forces that hold the protons and neutrons in the nucleus of an atom together are much stronger than the electric forces between the protons and electrons of the atom. That is why much greater amounts of energy are released from nuclear reactions than from chemical reactions.
Learning Goal 7
Electric currents in the earth's interior give the earth an extensive magnetic field, which we detect from the orientation of compass needles.
Learning Goal 8
The motion of electrons is far more affected by electrical forces than protons are because electrons are much less massive and are outside of the nucleus.