In learning this unit, students will explore Newton’s law of gravitation, which explains how objects attract each other. They will understand that gravitational forces follow Newton’s third law, meaning every action has an equal reaction. Students will discover gravitational fields, which illustrate how gravity affects objects in space, and they will define weight as the force due to gravity. They will learn to calculate the mass of Earth, solve problems related to gravitation, and see how the strength of gravity decreases with altitude. Finally, students will understand the importance of Newton’s law in explaining satellite motion. Overall, this unit will provide a clear understanding of gravity and its effects on our world.
THE FORCE OF GRAVITATION
Based on his observations, Newton concluded that the force that makes an apple fall to the ground is the same force that keeps the moon in its orbit around the Earth. He realized that every object in the universe attracts every other object, and he called this force “gravitation.”
According to Newton’s law of universal gravitation, every object attracts another object with a force that depends on two things: the masses of the objects and the distance between them. Specifically, the gravitational force increases if the masses are larger and decreases if the distance between them is greater. This means that if you double the mass of one object, the attraction between the two increases, and if you double the distance between them, the attraction decreases by a factor of four. This law helps us understand how objects interact in space, from falling apples to orbiting planets.
LAW OF GRAVITATION AND NEWTON’S THIRD LAW
OF MOTION
When one mass m1 attracts another mass m2, they exert forces on each other. Specifically, m1 pulls m2 towards itself with a force F. At the same time, m2 pulls m1 towards itself with the same force F, but in the opposite direction. If we consider the force exerted by m1 on m2 as the action, then the force exerted by m2 on m1 is the reaction. This means that both forces are equal in strength but act in opposite directions. This relationship aligns perfectly with Newton’s third law of motion, which states that for every action, there is always an equal and opposite reaction. In summary, the gravitational attraction between two masses illustrates this fundamental principle of physics.
ARTIFICIAL SATELLITES
An object that orbits a planet is called a satellite. For example, the moon is a natural satellite of the Earth because it revolves around our planet. In addition to natural satellites, scientists have launched many artificial satellites into space. Most of these artificial satellites orbit the Earth and are commonly used for communication. They carry instruments or even passengers to conduct experiments in space.
There are many artificial satellites in different orbits around the Earth, and they take varying amounts of time to complete one full revolution, depending on their distance from the Earth. Communication satellites, for instance, take 24 hours to orbit the Earth. Since the Earth also rotates on its axis in 24 hours, these satellites appear to stay in the same position relative to the ground, which is why their orbit is called a geostationary orbit. Dish antennas on Earth send and receive signals from these satellites and are fixed in a specific direction based on their location.
