What two factors affect the force of Gravity? Gravity It s Universal it s everywhere!

What two factors affect the force of Gravity? Gravity It s Universal it s everywhere!

Force The Standard Theory Boson (composite particle) Function Gravity Graviton Gravity curves space. And it always attracts, never repels. Gravity is the only force to which all particles are subjected. Range Indefinite (property of matter) Strong Nuclear Force Electromagnetism Photon Gluon (8 kinds) The strong force binds quarks into nucleons and nucleons into nuclei. Electromagnetism binds electrons to the nucleus. By doing so electromagnetism allows all physical and chemical processes to happen. Limited to the atomic nucleus (Nuclear Force) Indefinite (property of matter) Weak Nuclear Force Weak bosons (3 kinds) The weak force causes unstable particles and nuclei to decay. Limited to the atomic nucleus (Nuclear Force)

Newton s Law of Universal Gravitation G is a very small number (0.0000000000667) Gravity is a weak force, this means that the force of gravity is not noticeable unless there is a very large mass involved (such as a planet or star). That s why we are not revolving around one another! But the Earth and Moon are large enough! Gravity is universal it s everywhere!

Gravity depends on mass (amount of atoms) Less mass means less gravitational force More mass means more gravitational force

Newton s Law of Universal Gravitation Gravity pulls objects in a straight line towards each other. Earth and Moon

Gravity depends on the distance between objects More distance means less gravitational force Less distance means more gravitational force Think of gravity like a magnet. When magnets are closer, the attraction is stronger. When magnets are further apart, the attraction is less.

What two factors affect the force of Gravity? Gravity It s Universal it s everywhere! MASS DISTANCE

Gravity Gravitational Force Affected by mass and distance The amount of Newtons that gravity pulls on an object Gravitational Acceleration How fast an object falls due to gravity Called little g On earth little g = 9.8m/s/s F = ma Force of gravity will accelerate a mass. So an object speeds up by about 10m/s every second when falling On the moon little g = 1.6m/s/s So an object speeds up by about 2m/s every second when falling

Gravitational Acceleration So all objects want to fall at 9.8m/s/s on the surface of the earth. Gravity mini-experiment: 1. Crumble up (compress) a piece of paper. 2. Drop the paper from the height of your desk to the floor. 3. Leave a piece of paper flat. 4. Drop the paper from the height of your desk to the floor. 5. Observe how each object falls. Discussion: Both object want to fall at 9.8m/s/s. Did each object fall at the same rate downward? What did each object have to push through? What would happen if the paper had nothing to push through? Hammer vs Feather Physics on the Moon

APOLLO 15 THE HAMMER AND THE FEATHER All objects fall at the same rate in a gravitational field. Normally air resistance would slow down the feather. On the moon there is no air so it is easy to see that gravitational fields accelerate all objects at the same rate.

ADJUSTING TO LIFE BACK ON EARTH Astronauts in Space Washing your hair in space! Washing your bald head in space? Sometimes astronauts have a little trouble adjusting to life back on Earth Adjusting to Life back on Earth Text: Zoltan Otvos Graphics: Andras Danscak Source: NASA/Nepszabadsag Graphics

Gravitational Acceleration All objects on the surface of the earth accelerate downward at 9.8 m/s 2 regardless of mass. Why? (Think about inertia ) Remember F=ma As the force and mass change the acceleration stays the same. 100 kg 10 kg Gravitational acceleration g = 9.8 m/s 2 Gravitational acceleration g = 9.8 m/s 2 More mass means more gravity, but it also means more inertia. The extra gravity gets cancelled out by the extra inertia, so all objects fall at the same speed regardless of mass.

Gravitational Acceleration Once the altitude becomes comparable to the radius of the Earth (a distance thousands of miles away from earth), then the gravitational acceleration becomes much smaller. Once you are about 20,000 miles above the surface, there is little gravity this is known as microgravity.

Weight Gravity s Effect on Mass Weight = Mass x Acceleration of Gravity W(Newtons) = m (kg) g(meters/sec 2 ) 9.8 (Newtons) =1 (kg) 9.8(Meters/Sec 2 ) Weight is a Force measured in Newtons As you travel further from the surface of earth, increasing distance, then the gravitational force and gravitational acceleration decrease. If you travel far enough then you have apparent weightlessness.

Word Magnet: What is Gravity? Attractive force Gravitational Force depends on the total mass of the two objects Property of Matter Gravity Considered to be a weak force Gravitational Force depends on the distance between the two objects One of the four forces of nature

GRAVIT Y TENNIS Procedure: 1. Hold one tennis ball at the height of the counter. 2. Roll the second tennis ball from the back of the counter to the front edge. 3. Once the rolling ball reaches the edge of the counter, let go of the first tennis ball. 4. Observe the motion of each ball and repeat for several trials. Discussion Questions: Did the tennis balls hit the ground at the same time? Explain. How fast do objects want to fall vertically on the surface of Earth? Does horizontal motion influence or change the vertical motion?

INVESTIGATING GRAVIT Y

INVESTIGATING GRAVIT Y

INVESTIGATING GRAVIT Y Think about Newton s First Law? Does the cup have mass? Does the water have mass? Are the cup and water moving at the same rate? How fast does little g want to accelerate all objects?

Chapter 3.1 Gravity Topic: What affects the force of gravity? Vocabulary (Define in your notebook): Gravity Weight Orbit Procedure: Complete using Window Notes Define the vocabulary words in your notebook. Paragraph read section 3.1 (pages 76-83) with your lab group. Answer questions 1-6 on page 83 in your science notebook Extension Activity - Gravity and Orbits Interactive