Physical Science 8th grade (1).pdf

Because this acceleration is used so frequently in

• JusticeIce1840
• 395

This preview shows pages 309–311. Sign up to view the full content.

Because this acceleration is used so frequently in physics, the letter g is used to represent its value. When you see the letter g in a physics question, you can substitute the value 9.8 m/s 2 . Gravitational force, mass, and distance Gravitational force exists between all objects that have mass. Newton’s law of universal gravitation says the strength of the force depends on the mass of the objects and the distance between them. The greater the masses and the smaller the distance, the greater the force. You do not notice gravity between ordinary objects because it takes a huge amount of mass to create enough force to notice. You feel the force of gravity between you and Earth because the planet’s mass is huge. Weight Your weight is the force of gravity between you and Earth. It depends on your mass, Earth’s mass, and your distance from Earth’s center. You calculated weight with the formula W=mg . The g in the weight formula is the same g that describes the acceleration due to gravity. The value of g depends on Earth’s mass and the distance between its center and surface. If you travel to a planet or moon with a different mass and/or radius, the value of g and your weight would change.

This preview has intentionally blurred sections. Sign up to view the full version.

302 U NIT 5 M OTION AND F ORCE Orbital motion Gravitational force and acceleration Newton’s second law can be used to explain the motion of planets, moons, and satellites in orbit. For example, the moon moves in a 384,000 km orbit around Earth at nearly constant speed (Figure 14.16). While the moon’s speed is constant, its direction is not. Therefore the moon is accelerating. The gravitational force between the Moon and Earth causes the acceleration. Why the moon doesn’t fall to Earth The moon orbits or moves around Earth just as Earth and the other planets orbit the sun. But why doesn’t the force of gravity just pull the moon into Earth? To answer that question, imagine kicking a ball off the ground at an angle. If you kick it at a slow speed, it curves and falls back to the ground. The faster you kick the ball, the farther it goes before hitting the ground. If you kick it fast enough, the curve of the ball’s path matches the curvature of Earth. The ball goes into orbit instead of falling back to Earth. The moon falls around Earth The same idea applies to the motion of the moon. The orbiting moon falls around Earth. But as it falls, Earth curves away beneath it. What do you think would happen if the gravitational force between the moon and Earth were to disappear? The moon’s inertia would cause it to move in a straight line at a constant speed. The moon would fly off into space! Satellites Many human-made satellites orbit Earth providing weather data, communications services and scientific research. These satellites orbit much closer than the moon and must be launched at speeds high enough to reach orbit and not fall back to Earth.
This is the end of the preview. Sign up to access the rest of the document.
• Fall '10
• ALLISON

{[ snackBarMessage ]}

What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern