Laws of Gravity Luke – I am your Father! NOOOOO OOOOOO OOOOOO OO!!!

2 - Friction and Gravity What is Gravity? Gravity is the attractive force between all objects with mass in the universe. Gravity PULLS all objects toward eachother.

3 How Gravity Works Therefore, the earth is trying to pull us towards it’s center and we’re trying to pull the earth towards our center. (Newton’s 3 rd Law) Gravity pulls you towards the center of any object w/ mass.

4 - Friction and Gravity Laws of Gravity Two factors affect the “gravitational attraction” between TWO OBJECTS: MASS and DISTANCE. Use the magnets as a demo.

Mass Lets see how “Mass” effects gravity first

6 Mass, Weight & Gravity Everything with mass has gravity. –Mass is what gives any object gravity. More mass = more gravity Weight really is a measurement of the gravitational attraction between you and the earth. Remember – Weight is a Force

7 Changes in Mass Mass: 44.4 kg Weight: 100 lbs or N Mass: 88.8 kg Weight: 200 lbs or N A. I would add more mass and therefore weigh more. 0kg 10kg 100N 0N Mass Weight Q. If I weighed 100 lbs then continually overate, what would happen to my weight?

8 Changes in Mass Mass: 44.4 kg Weight: 100 lbs or N Mass: 88.8 kg Weight: 200 lbs or N Notice that If I add more mass, I increase my weight, or the attractive gravitational force between me and the planet earth. (Note the thickness of the attractive force between us.) A. I would add more mass and weigh more.

9 Mass & Gravity In other words: If you add more mass – you’ve increased the attractive force between you and the earth. –You therefore “Weigh” More.

10 Changes in Mass If your mass stayed the same, but the planets mass increased, your weight would also increase because of the attractive force of gravity of the planet increased. Q. If I weighed 100 lbs then went to another planet with more mass – what would happen to my weight then? Q. If I weighed 100 lbs then went to another planet with more mass – what would happen to my weight then? Mass earth : 6 x10 24 kg Your Weight: 100 lbs or N Mass earth : 6 x10 24 kg Your Weight: 100 lbs or N Mass Jupiter : 1,900 x10 24 kg Your Weight: 318 lbs or 1052 N Mass Jupiter : 1,900 x10 24 kg Your Weight: 318 lbs or 1052 N Jupiter’s gravitational attraction is 318 times greater than Earths because it’s 318 times more massive! Notice the thicker line of attractive force?

11 Changes in Mass Mass Weight 0kg 10kg 100N 0N Notice that the person’s weight has increased but his mass stays the same. The only difference is the mass of the planet! 300N

12 Mass & Gravity In other words: If the planets mass increased – the planet increased the attractive force between it and you. –You therefore “Weigh” More.

13 Your Weight on Other Worlds Illustration of how different masses affect gravity Click on the astronaut to pull up a weight calculator on a website

Distance Now, lets see how “Distance” effects gravity.

15 Laws of Gravity: Distance The closer you are to the object, the more your going to feel the effects of gravity. The farther you are from the object, the less your going to feel the effects of gravity.

16 Let’s see how distance from the center plays a major roll in your weight. Distance from the center of Gravity matters! No Difference Huge Difference These two people are the same distance from the center of the earth, therefore, the pull of gravity is the same! As the Astronaut gets farther away, The effects of Earth’s gravitational pull is less Let’s see what happens when we get farther away.

17 Mass & Weight Mass Weight 0kg 1000kg 1N 0N Notice that on earth my mass is the same in space – it didn’t change. However, on earth my weight is 1 Newton, but it’s zero in space.

18 Distance & Gravity can change! In other words, If I leave the earth and head to outer space, I’m not likely to feel the gravitational attractive force. –I therefore, weigh less. Dude! I CAN FLOAT AROUND! If distance increases, the force of gravity decreases.

19 Formula for Gravitational Force M1M2 d d M1 M2 Attractive Force g The Force of Gravity (Pull) = the mass of two objects Divided by the distance 2 What this formula means is that gravity increases with mass and decreases with distance. Masses are closer = more gravitational pull Masses are farther = less gravitational pull

20 Gravity and the Laws of Motion Recap Newton's 1 st Law: Inertia –Objects with mass have inertia – a resistance to change in motion. Objects at rest will stay at rest unless something “pushes” it. Objects in motion will stay in motion unless something “pulls” on it. Newton’s 2nd Law: F = M x A –In order to get any object w/ mass to move, you must apply a force. Newtons 3rd Law: For every action, there is an equal and opposite reaction. –When a force is exerted - an equal opposite force occurs. Let’s see how these laws affect the next scenario in space.

21 What would the scale read if you weighed yourself out in space? What would the scale say about the weight of the anvil in space? Are the both of you mass-less? How did Distance play in this roll? Remember: Weight is a force – it depends on the attractive force of gravity. mass does not. Force = Mass x Acceleration Weight = Mass x Gravity Therefore, you still have mass, but you are “weight”-less.

22 If you tried to push the Space Station; what do you predict would happen? You’ve got to be kidding me! The Space Station has a lot of inertia because of mass. Because of the large amount of inertia it’s hard to move. And yet simultaneously, it would also be weightless. Let’s look at inertia in space! Roger Houston! Here I go! Why does the astronaut fly backwards when he tries to push the space station? How does this relate to two people (one large & one small) pushing each other on skateboards?

23 Gravity is what effects all of the motion in space. Would any of the planets orbit the sun if the sun had no gravity?

24 Gravity is what keeps all planets in orbit. It’s like an invisible rope that links both the sun and the earth together. As the planet moves forward, it also simultaneously falls towards the sun – hence it’s path is circular.

25 Q. What would happen if the sun suddenly disappeared? From the top of the orbit, would it go: a.Away from the source towards the top? b.Away from the source at 45°? c.Away from the source towards the left? A. Without the gravitational pull of the sun, the earth would go straight from the immediate direction it was taking at the moment. b c a

26 Conclusion Gravity is dependant upon the mass of two objects and the distance between them. –If mass increases – Force of Gravity increases –If distance increases – Force of Gravity decreases. Jupiter has more mass than Earth; Therefore it has more gravity The satellite is farther from the center of Earth than we are; Therefore the satellite “feels” less pull of gravity