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

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

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

Gravitational Acceleration So all objects “want” to fall at 9.8m/s/s on the surface of the earth. Gravity mini-experiment: Crumble up (compress) a piece of paper. Drop the paper from the height of your desk to the floor. Leave a piece of paper flat. 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? Answer in your notebook

THE HAMMER AND THE FEATHER APOLLO 15 THE HAMMER AND THE FEATHER http://www.teachertube.com/video/hammer-and-feather-drop-on-moon-41342 Before you watch the video. 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 http://www.space.com/ 21946-how-to-wash- hair-space-video.html Sometimes astronauts have a little trouble adjusting to life back on Earth Washing hair in space: http://www.space.com/23672-adjusting-to-life-back-on-earth-karen-nyberg-talks-to-space-com-video.html Adjusting back to life on Earth:

Gravitational Acceleration All objects on the surface of the earth accelerate downward at 9.8 m/s2 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 Write this in your notes! Gravitational acceleration g = 9.8 m/s2 Gravitational acceleration g = 9.8 m/s2 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.

Weight W(Newtons) = m (kg) g(Meters/Sec2) Read this slide! Gravity’s Effect on Mass Weight = Mass x Acceleration of Gravity W(Newtons) = m (kg) g(Meters/Sec2) 9.8 (Newtons) =1 (kg) 9.8(Meters/Sec2) 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? Write this in your notebook! Considered to be a weak force Attractive force Gravitational Force depends on the total mass of the two objects Gravitational Force depends on the distance between the two objects Gravity One of the four forces of nature Property of Matter

INVESTIGATING GRAVITY

INVESTIGATING GRAVITY Answer in your notebook

INVESTIGATING GRAVITY Read through these before you look at the next slide. You do NOT have to answer these in your notebooks. 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 When you complete the notes start working on your homework.