01.04 Forces in Action

Distance

Distance: The greater the distance between the objects, the weaker the gravitational force between them. The strength of a gravitational force decreases with an increase in distance. We know that the Sun has a stronger gravitational force than the Earth because it has a lot more mass than the Earth. However, because we are so much closer to the Earth, its gravity has a stronger affect on us than does the Sun's gravity.

Weak Forces

Don't let the name fool you! Weak Nuclear Force is a very powerful force; it is given its name because there is another nuclear force that is even stronger. The weak nuclear force is responsible for different types of particle decay and radioactivity, including beta decay. Beta decay can occur in two ways. beta decay © 2009 FLVS dLink-processing data A neutron changes into a proton by emitting a negatively charged beta particle. In the second form of beta decay, a proton changes into a neutron by emitting a positively charged beta particle. Both types of decay produce radioactive beta particles, and the change in the number of protons and neutrons in the atom's nucleus results in a new element being formed. Radioactivity occurs when the nucleus of an unstable atom breaks down, releasing charged particles and energy. Beta decay can occur when an atom's nucleus has too many protons or too many neutrons. Unlike gravity and electromagnetism, weak nuclear force has a very short range. You must be near the unstable atoms to be affected.

electromagnetic forces

Electromagnetic forces are the second strongest of the four fundamental forces, second only to strong nuclear forces. Electromagnetic forces are the only forces that can both attract or repel each other, depending on the charges. Electricity, magnetism, static, light, the electromagnetic spectrum, and the bonds and attractions between atoms, ions, and molecules are all examples of electromagnetic forces. Magnets on your refrigerator are attracted to the refrigerator by electromagnetic forces. Electromagnetic interactions in your computer screen generate light that allows you to read the screen. The electromagnetic force attracts negative electrons to the positive nucleus of an atom and underlies the interactions between atoms and molecules. Text Version This force also has a very long range. Its attraction and repulsion cannot reach over as long a distance as gravity's attraction, but its range is still much greater than the short ranges of strong and weak nuclear forces.

Gravity

Gravity is a force of attraction between two objects that depends on two things: mass and distance.

Mass

Mass: The greater the mass of two objects, the greater the gravitational force between the objects. Humans do not feel the Sun's gravity pulling on them but the Sun's strong gravitational force keeps the Earth in its orbit! Because the Earth has a much greater mass than a human being, it feels a stronger gravitational force from the Sun than we do.

Understanding Gravity

Newton discovered the Law of Universal Gravitation prior to discovering the Laws of Motion. The Law of Universal Gravitation tells us that every object in the universe is attracted to one another by a force. How much they are attracted to each other depends on the object's mass and the distance between them. Einstein's Theory of General Relativity added a new perspective on gravity by introducing the concept of a four dimensional universe. He theorized that the mass of an object distorts space time. Although Einstein's description of gravity is very different from Newton's, they both describe the weak gravitational forces in the same way. However, Einstein's theory does a more accurate job of describing strong gravitational forces. Both Newton and Einstein have contributed to our understanding of gravitational force.

Is the Moon affected by the Earth's gravity? If it is, why has it not crashed into the Earth?

The Moon is in orbit around the Sun as well as around the Earth. As the Moon orbits around the Earth, they are both orbiting around the Sun together. The Sun's strong gravity is pulling on the Moon and the Earth, so they stay together without the Moon crashing into the Earth.

Strong Forces

The Strong Nuclear Force is an attractive force that holds the nucleus of an atom together. It is associated with holding the protons and other subatomic particles together inside the nucleus. As you saw in electromagnetic forces, like charges naturally push against, or repel, each other. The protons in an atom's nucleus all have a positive charge, so they naturally repel each other. The strong nuclear force overrides the electromagnetic repulsion and is able to hold the positive protons and neutral neutrons packed tightly together in an atom's nucleus. As its name suggests, strong nuclear force is the strongest of the four fundamental forces, but it has a very short range that does not reach far beyond an atom's nucleus.

When a spaceship is in orbit around the Earth, the astronauts are able to float weightlessly inside. Why are they weightless in space even though they have weight on Earth?

The reason that astronauts feel weightless actually has to do with their position compared to their spaceship. We feel weight on Earth because gravity is pulling us down toward the center of the Earth, but we press against the floor or ground as it stops us from falling. Any ship in orbit around the Earth is falling slowly to Earth. Since the ship and the astronauts are falling at the same speed, the astronauts do not press against anything, so they feel weightless inside the spaceship.

When a spaceship is outside the Earth's orbit, does it experience any gravity?

Yes, there is gravity everywhere in the universe. It is a force of attraction between objects that gives shape to planets, solar systems, and even galaxies. Gravity from our Sun reaches throughout our solar system, keeping the planets in their orbits.