Gravitation Lindy Lou Yamilo Cyren Andit Rochel Agbayani Earl Jan Tampus III-Galileo

Gravity is a fundamental force in the sense that it cannot be explained in terms of any other force. Four Fundamental Forces 1. Gravitational 2. Electromagnetic 3. Weak nuclear 4. Strong nuclear force

If there is no gravity…….. Gravity is that force that holds you in your seat. If I pull the chair out from under you, what will happen? If we could turn gravity off, we would all float around like the astronauts in the space shuttle do while the shuttle is in orbit around the earth.

Example: How much force holds a 220-pound man in his seat in newton? Answer: 220 pounds x 1 kg/2.2 pounds = 100 kg Applying the equation for weight w = mg = 100 kg (9.8 m/s2 ) = 980 N The force is 980 N directed upward, as opposed to his weight is directed downward.

How can your weight change? Your weight on Earth, or the force that pulls you toward the ground, is the pull of Earth’s gravity on you. If you want to calculate how many newtons of force hold you in your seat Weight = mass x acceleration due to gravity or w = mg Where weight is in newtons, mass in kg, and acceleration due to gravity on earth is 9.8m/s2.

Example: From the previous example, how much does he weigh on the moon if the gravity is 1/6th that of the earth? What is the acceleration due to gravity on the moon? Answer: Since your weight on the earth is 980 N, and the gravity of the moon is 1/6th that of the earth, then just divide your weight on the earth by 6. Weightmoon= 980 N/6 = 163 N

To solve for gmoon, again, just divide gearth by 6. gmoon = 9.8 m/s2 /6 = 1.6 m/s2 Weightlessness When you can feel weightlessness? There are two basic ways. You can be far enough away from all large objects in the universe that the force of gravity due to them cannot be felt. Or you can be in free fall. One form of free fall keeps amusement parks in business. When you are falling toward the Earth with an acceleration of 9.8m/s, you feel weightlessness. No force pushes you unto your seat

and stomach seems to have moved north to make friends with your heart and lungs. The mst current rage is the drop you, you can see if there is any force left to hold the penny on you knee, if not, then the penny will “float” up as you fall, and you can prove that you really were in free fall.

Kepler’s Laws of Orbital Motion

In 1617, before Newton saw that gravity is a universal phenomenon that affects the earth and beyond the skies, German scientist Johannes Kepler had observed the motion of the planets and formulated his Three Laws of Orbital Motion. First Law: Law of Orbits - all planets move in elliptical orbits with the sun at one focus.

Newton’s law of gravitation

The Gravitational Constant A measurement of the gravitational force between two known masses a known distance apart is needed. The value G was finally established in 1789, more than a century after Newton’s work, by Henry Cavendish. He used an instrument called a torsion balance. The value of the gravitational constant G is found to be G = 6.67 x N-m 2/kg2

The Gravitational Equation

Example

The increase in the scale reading is therefore m= F/g = 7.4 x 10-8 N / 9.8 m/s2 = 7.6 x kg So it is hardly worth the effort. The Gravitational Field -region surrounding a mass or body where another body experiences a force of attraction due to the first body. In simple terms, there is a gravitational field around the earth, and it affects a body by giving it an acceleration due to gravity g, as determined by Newton’s Law of Gravition.

Pendulum Motion Another way of deriving g is by using pendulums. A simple pendulum is just a mass suspended by a ‘mass less’ or a string with negligible mass. Starting from a certain height an allowed to swing freely, it will move along a curved path, moving back and forth. This could be assumed as uniform circular motion with a period Ʈ, so we can use the following equation